Ecologist's Notebook

Utah juniper tree. Photo by A. Levine, Wikimedia Commons

(Click on the following link to listen to an audio version of this blog … Junipers and potholes )

Edward Abby had more than a couple of things to say about juniper trees in his book Desert Solitaire:

“The essence of the juniper continues to elude me unless, as I presently suspect, its surface is also its essence.”

“If a man knew enough he could write a whole book about the juniper tree. Not juniper trees in general but that one particular tree which grows from a ledge of naked sandstone near the old entrance to Arches National Monument.”

Junipers stand out against the rocky expanse of the Colorado Plateau steppes. Their deep, living green contrasts with the tans and red-browns of the sand and rocks and with the gray-greens of the scattered sagebrush. That they can live here on the edge of the desert, that they can exist where almost no other green thing can, is a story worth exploring. They stand, as Abby implied, at the edge of an infinite complexity of wonder!

Photo by D. Sillman

There are two common species of juniper around Arches and Canyonlands National Parks: Utah juniper (Juniperus osteosperma) and one-seed juniper (J. monosperma). These two species resemble each other: both have short, straight trunks with spreading branches, very small, yellow-green, scale-like leaves (on adult trees) and light blue “berries”  (which are really ripe, wax-encased, seed cones). On very young seedlings the leaves are green, needle-shaped and just under 1/2” long.  One-seed juniper trees are usually smaller and bushier than Utah junipers. Also, their “berries” are usually slightly smaller. The two trees, though, are very difficult to tell apart, and, making absolute identification even more challenging, the two species also cross-pollinate and form intermediately configured hybrids.

These junipers can be between 10 and 26 feet tall, and, like sagebrush, have two types of root systems: a deep taproot that can be up to 25 feet long, and a shallow, spreading fibrous root system that can extend up to 100 feet around the plant. The tap root allows the juniper to access water from the underlying water table and the fibrous roots enable it to take up rainwater and snow melt before it gets into the deep water table. Interestingly, the fibrous root systems are inactive in the summer (a time when there are few rain events). Snow melt is probably the main source of water picked up by these shallow, fibrous roots.

Utah juniper. Photo by fcb981. Wikimedia Commons

Junipers grow very slowly and add only 0.05” to their trunk diameters each year. They are, however, very long-lived and can reach ages in excess of 650 years!

Junipers are mostly monecious (only one type of individual that has both pollen and ovulate cones). They begin to produce seeds at 30 years of age and, thereafter, make abundant seeds almost every year. Each “berry” contains one or two seeds. Many mammalian and avian species rely on juniper “berries” for food, and the juniper in turn relies on these consumers to transport and disperse the seeds and also scarify them. Juniper seeds germinate much more readily after they have passed through the intestines of a seed-eating mammal or bird.

Junipers also often have white berries growing among their dense branches. These are the fruits of two mistletoe species (juniper mistletoe (Phoradendron juniperum, ssp juniperum) and dense mistletoe (P. boleanum ssp densum)) which very commonly parasitize both Utah and one-seed junipers.

Pinyon-juniper woodland shrubland. NPS, Public Domain

Junipers are most often are found growing with pinyon pines (Pinus edulis). These pinyon-juniper woodlands are quite productive and are expanding into formerly sagebrush areas primarily due to human activity (see Signs of Summer 6, June 23, 2022). Suppression of natural fires has allowed some sagebrush communities, which historically got “re-set” every few decades by burns, to develop into pinyon-juniper woodlands. And, the more intense and more frequent occurrence of modern wildfires (fueled by the presence of invasive species and the extended dryness and heat due to climate change) have wiped out unnaturally large areas of sagebrush leaving little chance of natural re-vegetation with seeds from the poorly transported sagebrush species.

Young juniper trees are very vulnerable to fire and are easily killed in even low intensity fires. Older, larger trees have some resistance to fire damage. Natural fires in pinyon-juniper woodlands have historically cycled over every 10 to 30 years.

Pronghorn Antelope, Cabin Lake Road, Fort Rock, Oregon

Many small mammals (including desert cottontails, porcupines, deer mice, Great Basin pocket mice, desert woodrats and kangaroo rats), and reptiles (including collared lizards, plateau lizards and tree lizards) rely on pinyon-juniper woodlands for habitat. Also over 70 species of birds breed in pinyon-juniper woodlands including five species that locally do so obligatorily (screech owls, gray flycatcher, scrub jay, plain titmouse and gray vireo). Ferruginous hawks also nest in Utah juniper trees.

Large mammals (like mule deer, elk, bison, pronghorns, wild horses, mountain lions and lynx) also inhabit pinyon-juniper woodlands. These woodlands provide these species very important protective cover both in the summer and in the winter.

Photo by D. Sillman

Juniper leaves are very poor quality browse. They are quite low in nutrients and have high levels of volatile oils which can poison a ruminant’s vital stomach microflora. In the winter, though, when browse is scare, mule deer do consume juniper foliage.

A very unusual feature of a juniper is its ability to prune back its own branches in order to conserve water. Most older juniper trees have large, dead branches still attached to the main, living trunk of the tree. The trees are able to shut down waterflow to those branches in order to keep sufficient water available for the rest of its tissues.

Dry potholes at Grand View Point. Photo by M. Hamilton

When we were out on the big, slick-rock expanse looking over the canyon at Grand View Point, I noticed a whole set of crust-lined concavities all across the rock. The depressions were between 3 and 8 feet long and each one was about half as wide as it was long. The largest of the “potholes” had depths of 4 or 5 inches below the rock-face surface at their deepest points with much shallower areas around their peripheries. All of them, though, regardless of size, were uniformly lined with similar-looking, flaky, greenish-gray coatings.

There were about 20 of these concavities immediately visible across the open rock face where I was standing but many more off in the more vegetated (juniper trees and black-brush clumps, primarily) edges of the rock. There were a very large number of these concavities, then, all along the rocky top rim of this canyon!

Potholes in sandstone. J. St. John. Flickr.

Using some very rusty geometry, I calculated that the larger holes had individual volumes of about 31 gallons (or 117 liters), and that the smaller ones were closer to ten gallons (or 38 liters).  All of the depressions I could see had a summed volume of just over 400 gallons, but this volume represented just a fraction of the total potential pool size across the miles and miles of rock circling the top rim of the canyon. These little “potholes” could collectively hold a very large volume of water from snow melt or spring rains!

These potholes, when filled with water, are called “desert rock pools” or “freshwater rock pools.” They are the desert counterpart of the temporary, “vernal” pools found in the wet forests of the eastern part of North America (see Signs of Spring 10, April 28, 2016) or, maybe more accurately, miniature versions of the playa lakes of the southern plains (See Signs of Winter 4, December 24, 2020). They are extremely ephemeral bodies of water in a climate where water is the preeminent ecological limiting factor.

These rock pools are miniature, oligotrophic (“low nutrient”) ponds. Nutrients in them can only come from air-borne organic materials or from feces deposited by terrestrial animals. Primary productivity (photosynthesis) in the pools is quite limited and for the most part carried out by cyanobacteria. As we saw in biological soil crusts, cyanobacteria are able to survive severe desiccation and can rehydrate quickly back into fully functional, photosynthesizing cells. The bottom crusts of the dried pools are, for the most part, cyanobacteria residues. We should also note that, like the cyanobacteria residues in biological soil crusts, these rock pool residues are very susceptible to compression damage! Walking or wading through one of these pools can do a great deal of lasting damage to these vital bacteria.

Utah desert rock pools. Needpix.

When one of these pools fills with water a number of species of crustaceans, flatworms, rotifers, mites and tardigrades rush to complete their life cycles. As the water evaporates, these organisms, if they have developed quickly enough, sink back into their drought resistant life stages (eggs, larva or even adult forms) and bury themselves in the dry, protective crust of the pool’s sediment.

These “passive dispersing” life forms move from pool to potential pool by high, seasonal water flows or wind. Animals walking through the dried crusts can also transport the active or inactive life stages of these organisms from one pool site to another.

The pool also sustains a number of “active dispersing” species. These include many species of flies, midges and mosquitoes whose adult forms can fly from pool to pool to lay eggs. We were cautioned that in the early spring there are large numbers of biting midges out on the hiking trails of Arches and Canyonlands. These rock pools are, undoubtedly, one of the main sources of these organisms.

These pools are important signs of the overall health of these desert and dry steppe ecosystems. They are also quite important, in spite of their incredibly short-lived natures, in the early spring food chains for a number of bird and reptile species. The clouds of midges and mosquitoes to us humans are pests, but to a hungry, nesting, insectivorous bird or hunting lizard, they are mana from heaven (see Signs of Spring 13, May 19, 2015)!

Raven at Landscape Arch Trail. Photo by L. Drake

I had a few more “Moab” topics that I wanted to write about, but five blogs (7500 words) about these Utah ecosystems seems like enough for now! Sometime in the future I will write about ravens and cliff swallows, packrats and quicksand, and yuccas, Mormon tea and prickly pears! I’ll also try to get all of the incredible plant pictures that Deborah and Marian took and identified, organized and published. Stay tuned!!

“Desert” vegetation. Photo by D. Sillman

(Click on the following link to listen to an audio version of this blog …. Biological soil crusts, rock varnishes and kangaroo rats )

One of the main distinctions between an arid grassland and a desert is the abundance of bare soil in between a desert’s isolated clusters of plants. For centuries it has been recognized that these desert soils were not just random mixes of simple soil separates (sand, silt and clay particles). Instead, this soil was darker than it would be if it were only made up of soil particles. It was also lumpy and in a micro-topographic way, complexly structured with tiny turrets, folds, mounds and crevices. Initial names for these dryland soils often had the prefix “crypto” appended to them implying that they had a mysterious or hidden nature. They were, though, just sitting there out in the open waiting for detailed examination and description.

Cyanobacteria filaments. Photo by J. Golden, Flickr

Research teams of botanists and agronomists finally began to peel away the “crypto” nature of these dry soils in the late 1970’s and showed them to be complex micro-communities dominated by cyanobacteria (“blue-green algae,” one of the oldest photosynthesizing organisms on Earth (see Signs of Winter 9, February 13, 2020, and Signs of Summer 16, September 17, 2020)). These soil surface communities also contained green algae, lichens, fungi, mosses and a variety of other species of bacteria. All of these living organisms acted to stabilize the desert soil and nurture the surrounding plants in entirely unexpected ways. These thin, delicate encrustations, now called “biological soil crusts” (or, “biocrusts”) were, in fact, the living “top soil” of the desert! These patches of “bare” soil, in fact, contained more species than could be found in all of the surrounding desert vegetation!

Soil crust magnified 90X. USGS. Public Domain

Cyanobacteria make up to 95% of the biomass of a biocrust. These photosynthetic bacteria grow in long, filamentous strands that are woven around the individual soil particles. They need to keep themselves exposed to sunlight in order to power their photosynthetic metabolisms (so they can’t go very deep into the soil profile!). Cyanobacteria can tolerate extreme desiccation and are able to rapidly re-hydrate when moisture once again becomes available.  Dried filaments, when they re-hydrate, swell to ten times their desiccated volume thus storing a large volume of vital soil water. New filaments are slowly added to the fiber systems and, over years and decades and even centuries, the soil particles become tightly woven into a complex bacterial framework. The cyanobacterial filaments also secrete sheathes of mucopolysaccharides which act to further bind the soil separates together. These extracellular mucopolysaccharides persist and continue to cement the soil components together even during period of extreme filament desiccation.

Biological soil crust at Arches N. P. Photo by D. Sillman

The impact of these filaments and sheaths on the soil is profound. Erosion both by wind and by water is significantly reduced in soils stabilized by these filaments. The potentially destructive impact of raindrops striking exposed soil is also reduced by the hard barrier of the crust, and the dark color of the crust absorbs sunlight and speeds up the thawing of the soil in the Spring.

The complex soil structure generated by these filaments and sheaths forms aeration and water flow channels through the crust. It also generates complex, raised edge depressions on the soil surface that allows surface water to pool up and then seep down slowly into the soil  profile rather than simply running off in surface flow. Also, a number of the bacteria in the crust are nitrogen fixers (they remove molecular nitrogen from the air and convert it into chemical forms that can be utilized by plants). For many desert plants, this is the only source of nitrogen available to them!

Biological soil crust at Arches N. P. Photo by USGS, Public Domain

The crust also serves as a nutrient bed within which the seeds of many plant species germinate. As these plants begin to grow, the crust with all of its spaces and channels also facilitates root growth.

Biological soil crusts once covered all of the dry, exposed soils of Colorado Plateau. Livestock trampling and human activities, though, have greatly reduced the distribution of these crusts. The cyanobacterial filaments and mucopolysaccharide sheaths are very sensitive to compressional damage. A single footprint can destroy all of the underlying soil crust filament infra-structure and leave a scar that takes decades to repair. “Don’t Crush the Crust” is a theme widely advertised on the hiking trails throughout the Plateau’s National Parks.

Rock varnishes near Moab, Utah. Deborah in the foreground. Photo by M. Hamilton

Rock varnishes are thin, dark or reddish-brown coatings on desert rocks and cliff faces that were once thought to have origins similar to those of biological soil crusts. Recent research, though, has clearly shown that these hair-thin patinas, usually found on very sheltered rocks, are chemical in their origin rather than biological.

Rock varnishes (also called “desert varnishes,” or “rock rusts”) form when silica atoms either in the atmosphere or from the underlying rock itself slowly

Desert varnish. Photo by Ooinn, Wikimedia Commons

accumulate on the rock surface and weather into a stable, dry gel. This process is very slow and may occur over centuries or even millennia. The color of the varnishes often reflect the presence of iron oxides (reddish brown) or manganese oxides (black). There is an on-going debate about whether biological processes may play a role in accumulating these metallic oxides within the predominantly chemically generated films.

A remarkable feature of these gelled silica layers is that they trap biological materials in between their forming layers. Amino acids, fragments of DNA and even entire bacterial cells can be found encased between the microscopic silica layers of the varnishes! Analysis of the trapped materials in a rock varnish may reveal information about ecosystems and climates that existed on these sites thousands or even millions of years ago.

Native American petroglyphs (Newspaper Rock, southeastern Utah). Photo by J. St. John, Wikimedia Commons

Desert dwelling people use the rock varnishes as a canvas to etch art that depicted their lives and activities. The petroglyphs found throughout the American Southwest are examples of these “enhanced” desert varnishes!

Rock varnishes may also be present on rocks on Mars! New NASA probes and rovers exploring the Martian surface are programed to look for stained rocks and maybe even sample them as a way to explore the ancient history (and, possibly, the ancient biology?) of Mars!.

Kangaroo rats are creatures of the desert that are behaviorally and physiologically adapted to extremely dry conditions. The are primarily nocturnal and spend the hot, dry days sealed up in their cool, highly branched burrows about a foot or so underground. Their respiratory systems have long, upper respiratory tubes that are designed to minimize water loss during expiration, and their excretory and digestive systems are designed to form extremely concentrated, low moisture urine and feces. Kangaroo rats also never drink liquid water! They generate water metabolically from the carbohydrates and to a lesser degree fats in the seeds they eat.

Ord’s kangaroo rat, Photo by A. Teucher, Flickr

Ord’s kangaroo rat ((Dipodomys ordii) is very common in Arches and Canyonlands National Parks. This kangaroo rat is vital to the propagation and, possibly to the very existence of an important desert grass called “Indian rice grass” (Achnatherum hymenoides). Indian rice grass is a common, desert bunch grass that makes very large seeds (about half the length of a rice grain) in the late spring or early summer. Many wildlife species rely on rice grass seeds for food including Ord’s kangaroo rat.

Ord’s kangaroo rats gather the fallen Indian rice grass seeds in the summer and cache large percentages of them in shallow (three-inch deep) burrows. This depth, it turns out is ideal for these seeds to germinate! Further, the rats as they pick up and stuff the rice grass seeds into their cheek pouches for transport, scratch away the heavy protective coat on the seeds making them primed for immediate germination. Without this physical scarification, the rice grass seeds might remain dormant for years before germination!

The kangaroo rats gather and cache such an abundance of seeds, that the rats only recover about a third of them. The unharvested seed caches then germinate and grow into new clusters of Indian rice grass. It is estimated that 90% of Indian rice grass plants growing across the Colorado Plateau originate from Ord’s kangaroo rat seed caches!

Ord’s kangaroo rat,. NPS, Public Domain.

Kangaroo rats have very large back feet that they use for their “kangaroo-like” locomotory system of leaping and bounding. They also have very long tails with bushy ends that they use to keep their balance during their energetic jumps and leaps. Adult kangaroo rats are solitary and extremely antagonistic toward each other. This antisocial behavior, though, is quite adaptive in that it helps to keep kangaroo rat densities low in their resource-poor habitats.

I really didn’t expect to see any kangaroo rats on our Utah trip. Most of our hiking and outings were going to be during daylight hours, and kangaroo rats, like most desert animals, are well tucked away out of the reach of the hot desert sun during the day. However, the weather for most of our hikes was very mild (high temperatures only in the 70’s) and, like many species scrambling for limited resources, kangaroo rats can come out in the daylight if there is a good possibility of food.

Grand View Point, Canyonlands N. P. Photo by L. Drake

We were up on the rim of Grand View Point, seated on some well placed boulders that were scattered across a broad, slick rock base. The view across the canyon toward the distant confluence of the Green and the Colorado Rivers was breathtaking. We, and a number of other hikers, had stopped to have lunch and were subsequently entertained by the antics of two kangaroo rats who scuttled between the shady cover of the juniper and black-brush that were growing out of the creases and cracks in the rock. The rats, leaped here and there and chased each other about, but always kept their eyes open for any fallen bits of trail mix or sandwich crumbs.

Ari and I on a rock at Grand View Point. Photo by M. Hamilton

My grandson Ari and I were sharing a big sitting rock and had finished our peanut butter-and-jelly sandwiches. We split a handful of salted nuts for desert and several of nuts fell to the ground and rolled over to the edge of a black-brush bush. None of the lurking rats seemed to immediately notice the fallen nuts. After we finished our share of the nuts, though, we walked over to the edge of the canyon to take in the view. When we returned a few minutes later, all of the fallen nuts were gone. A lunch fit for a kangaroo rat!

I hope that they didn’t just bury them and forget where they are!

(Next week: juniper tree and desert potholes!)

Vegetation in Arches National Park. Photo by D. Sillman

(Click on the following link to listen to an audio version of this blog … Sagebrush )

When we drove out of the Rocky Mountains via Glenwood Canyon, we entered the sagebrush lands of Colorado Plateau. Big sagebrush (Artemisia  tridentata) is one of the more notable species of sagebrush found all across these arid, western plains. Sagebrush is not technically a desert plant, though, instead, it is considered to be a vital member of the dry, steppe plant community (steppes receive slightly more rain (7 to 16 inches per year) than deserts (which receive less than 10 inches of rain per year). Sagebrush is found from Nebraska to California and from New Mexico to Montana. It has the widest distribution of any shrub in North America.

There is a wide range of estimates of the area of western North America that was once covered with sagebrush. A frequently mentioned value, though, is 422,000 square miles (270 million acres), a very large chunk of the American west! Regardless of how much sagebrush we started with, though, most experts agree that to date, more than half of the original, pre-settlement sagebrush acreage has been lost primarily due to land clearing for agriculture and various range “improvements” for livestock forage. Also, unnaturally extensive and intense wildfires, driven in part by climate change, have also destroyed millions of acres of sagebrush (more on this below).

Big sagebrush. Photo by DcrJsr, Wikimedia Commons

Big sagebrush (and other sagebrush species) were once classified as an undesirable “range weeds” by the United States Department of Agriculture (USDA), and land managers were encouraged to eradicate them. More recently, however, the true nature of sagebrush has come to light. The presence of these tall, evergreen shrubs in their arid habitats, generates microenvironments under them, within them and around them that are favorable and sometimes even vital for the existence of hundreds of species of plants and animals. Big sagebrush is, quite decidedly, a keystone species in its biological community!

Writing in a series of USDA Technical reports in the early 2000’s, B. L. Welch compared the soil and plant communities under or near sagebrush with those away from the sagebrush cover and noted that in the proximity of sagebrush, plant diversity and abundance were higher, soil moisture and nutrient levels were higher and the growing season for plants was 28 days longer.

Sage grouse. Photo by USFWS, Public Domain

Welch further listed animals that were obligatorily dependent on sagebrush for their survival (including the greater sage grouse, Gunnison’s sage grouse, sage sparrow, Brewer’s sparrow, sage thrasher, pygmy rabbit and sagebrush vole). He also noted that 100 species of birds, 90 species of mammals, 60 species of reptiles and amphibians are at least partially dependent on sagebrush for food, habitat, reproductive sites and as a refuge from the extreme heat of the dry steppe environment. Also, 240 species of insects, 70 species of spiders and other arachnids, 133 species of plants (including 23 species of root hemi-parasitic paintbrushes and owl-clovers) and 24 species of lichen were associated with and benefited by sagebrush.  He also described the synergy between the sagebrush micro-community and the surrounding, soil surface  “biological crust.” (We will talk about biological crusts next week!)

Big sagebrush gets its species name (“tridentata”) from its three-pronged leaves. The leaves are small and are directly attached to nodes on its stem. They are also covered with fine, silvery hairs. The small size, the tight stem attachments and the covering hairs all help to reduce transpiration water loss from the leaves and increase the fitness of the plant in its very dry environment.

Photo by M. Lavin, Wikimedia Commons

Big sagebrush can be a foot and a half to over nine feet tall depending on the richness and, especially, the moisture levels of its soil. Big sagebrush can also have a very long lifespan with some plants reaching 100 years of age! Big sagebrush has two types of roots: a dense shallow set that quickly gathers any incoming precipitation from the surrounding soil surface, and a deep taproot that reaches down 3 to 15 feet often reaching the underlying water table. These tap roots brings up “deep water” that not only satisfies the sagebrush’s own water needs but also provides moisture to nearby plants. European settlers looking to establish farms in the dry steppes of the American southwest, looked for tall, big sagebrush as indicators of a deep, non-acidic soils with, potentially, high soil fertility.

Big sagebrush’s silver-grey leaves have an herbal, almost spicy aroma due to an abundance of secondary chemicals like camphor, terpenoids and a number of other volatile oils. The purpose of these chemicals is to protect the leaves from grazers and browsers and also, possibly, to serve as communication chemicals between plants (when a sagebrush is disturbed by a grazer, it releases a cloud of camphor and terpenoids which stimulate nearby plants to make more of these grazer-repellant chemicals).

Pronghorn Antelope, Photo by A. Wilson, Wikimedia Commons

Big sagebrush leaves are rich in protein (16%), fats (15%) an carbohydrates (47%) and are actually more nutritious than alfalfa! Domestic livestock, though, is not able to consume big sagebrush because of its volatile chemicals. This intolerance explains why many ranchers have treated sagebrush as a noxious weed! A number of native species (like deer, moose, elk, and especially, pronghorns and bighorn sheep) can, at need, eat big sagebrush leaves especially in the winter. One reference stated that these native species “belch off” the volatile secondary chemicals before they can poison their vital, mutualistic, gut bacteria. Sage grouse also readily eat sagebrush leaves (sagebrush leaves make up 60 to 80% of the sage grouses’ year-round diet). The absence of  gizzard in the sage grouse, apparently, allows the sagebrush leaves to pass through their digestive systems without excessive physical disturbance that would release the toxic, volatile chemicals from the leaf tissues.

Big sagebrush, Public Domain

The flowers of big sagebrush develop on stalks that rise up from its upper branches. The flowers are small, yellow and wind pollinated. Pollen is produced in great quantities in August and September and is a very well recognized cause of fall allergies. Abundant seeds are produced as a consequence of this pollination (up to 350,000 per plant). Seeds are dispersed by gravity and wind and also by ants (in particular, the western harvester ant (Pogonomyrex occidentalis)). Native Americans harvested the very abundant big

Flowering sagebrush. Photo by M. Harte, Forestry Images

sagebrush seeds and ground them to make a flour.

Sagebrush is able to reproduce both by seed and also by stem-sprouting from its underground rhizome. New plants arising from seed require much higher amounts of moisture than plants arising from root sprouts. The “mother” plant of these sprouts, apparently, provides both water and nutrients to its clonal offspring giving them a growth edge over seed-derived, sagebrush seedlings and also other plants. Seed dispersal into burn areas, however, is vital for sagebrush recovery following a wildfire.

Fire is a normal component of a natural sagebrush ecosystem. The abundance of oils in the tissues of sagebrush plants make them extremely flammable even when they are green and healthy. “Natural” fires, though, in a sagebrush community are usually rather limited in total land area that is burned, and they are of rather low, overall intensity. These “natural” fires historically occurred every 60 to 110 years, and once an area burned, it was quickly re-seeded with sagebrush from nearby, surrounding plants. The cycling of these natural fires created natural sagebrush ecosystems that were patchworks of differentially aged communities. It also kept the vegetative systems in sagebrush configurations. Suppression of these natural wildfires through human intervention, however, broke this ecological re-set pattern and caused aging, sagebrush communities to be replaced via succession by woodlands of pinyon pine and juniper. Millions of acres of sagebrush have been lost to pinyon-juniper forests because of the human interference in the natural fire cycle.

Cheat grass. Photo by S. Dewey, Utah State University, Bugwood.org

Modern fires in sagebrush habitats are quite different from historical, natural fires. Climate change has caused prolonged drought periods  and elevated summer temperatures throughout the west. These conditions have caused the sagebrush vegetative community to become very dry over very extended periods of time. Also, the modern sagebrush plant community now includes a number of invasive plant species that add considerably to the overall quantity of fuel available to support and feed a wildfire. In particular, the exotic invasive “cheat grass” (Bromos tectorum) is found abundantly throughout sagebrush areas. Cheat grass was accidently introduced to wheat fields in the United States in the late 19^th Century and has spread widely and rapidly across the west. When we were in Utah we saw cheat grass growing in the vegetative communities throughout the national parks. We even saw waves of cheat grass growing up through the dry, barren gravel of a number of parking areas! It is a tenacious and highly drought-tolerant weed!

Cheat grass- assisted wildfires burn much hotter than “natural” wildfires. They also burn over much more extensive areas. These expanded burn areas, then, are not efficiently re-seeded with sagebrush because of the greater distance the poorly transported sagebrush seeds must travel.  Also, because these cheat-grass assisted fires occur much more frequently than natural fires (the new fire cycle repeats itself, on average, every 5 years!) they eliminate any early, vegetative re-growth and very effectively prevent the sagebrush community from becoming re-established. Sagebrush, amazingly, is under a distinct extinction threat from these climate and invasive species augmented fires!

South of Moab, Utah. Photo by D. Sillman

(Click on the following link to listen to an audio version of this blog …. Colorado Plateau )

We leave Glenwood Canyon and follow the Colorado River out of the mountains. We are now in the province of the Colorado Plateau.

The Colorado Plateau is a vast region (130,000 square miles) dominated by  sedimentary rock. The Plateau has repeatedly, over hundreds of millions of years, en masse, risen up many thousands of feet and then eroded back down most of those feet. Amazingly, these rises and falls have occurred with little or no deformation in the Plateau’s rock layers. Compared to the nearby Rocky Mountain and Basin and Range provinces, the rock strata of Colorado Plateau just seem to bob up and down in geological time with little bending, folding or twisting. Layer after layer of sandstone, mostly tinted red from iron oxides but each distinctly colored and textured with their own base minerals and unique origin stories,  lie flat on top of each other like layers of a vast, geological cake.

The geologist Charles Dutton writing about this area back in 1885 noted that there seemed to be

“many short, abrupt ranges, or ridges, looking upon the map like an army of caterpillars crawling northward. At length, about 150 miles north of the Mexican boundary, this army divides into two columns, one marching northwest, the other northeast … This split in the main chain of cordilleras, forming the Basin and Range on the west and the Rockies on the east leaves between them the vast area of the Plateau country.”

The Colorado Plateau. Public Domain

The Colorado Plateau is roughly centered over the Four Corners region where the respective corner-angles of Colorado, New Mexico, Utah and Arizona come together. It is bounded by the Rocky Mountains to the northeast, the Rio Grande Rift to the southeast, the Mogollon Rim escarpment to the south and the Basin and Range province to the west. Ninety percent of the Colorado Plateau is drained by the Colorado River while the rest is drained by the Rio Grande.

The Plateau is covered mostly with sparse, desert and dry-steppe vegetation with scattered stands of pinyon pine (Pinus edulis) and juniper (Juniperus osteosperma) and montane forests of ponderosa pine (P. ponderosa) in the south and lodgepole pine (P. contorta var. latifolia) and quaking aspen (Populus tremuloides) in the north. Forests are found in sites that are positioned to more efficiently gather or retain the scant moisture delivered by winter snows and rare summer rains. On average the Plateau receives between 6 and 16 inches of precipitation a year with higher elevations gathering the higher amounts of rain and snow. In recent years, however, these “average” annual moisture levels have been only rarely met.

Grand View Point, Canyonlands National Park. Photo by L. Drake

The erosion that wears down these layers of sandstone is powered by water, ice and wind. Countering this downward erosion, though, is a tectonic uplifting of the Plateau (driven most recently by the lateral, underthrust of the Farallon Plate which also lifted the Rocky Mountains 65 million years ago) and also by an isostatic, upward rebound of the rock as the weight of thousands of feet of surface materials are eroded away. The Colorado River and its tributaries cut deeply into these rising rock layers and have carved the magnificent canyons and vistas seen in Canyonlands National Park, Glen Canyon and the Grand Canyon.

Arches National Park. Photo by D. Sillman

Adding to the complexities and possibilities of the Plateau, under the layers of rock is a 300 million year old salt bed that is thousands of feet thick. A relic of an ancient, evaporated  ocean, this salt layer has been compressed by the overlying rocks that at one time were, possibly, a mile thick. Under the pressure of these rocks, the salt became fluid and flowed, shifted and buckled causing the rocks above it to fracture and crack in very unique ways. These cracks led to the long sets  of narrow masses of surface stone called “fins”

Deborah looking over a set of sandstone fins in Arches N. P. Photo by J. Hamilton

and numerous, narrow slot canyons that are seen throughout the Plateau. The erosion of the fins (primarily by water and ice) then led to the formation of the natural bridges, arches, hoodoos and hanging rocks that make the Plateau landscape so surreal and unique.

Attesting to the uniqueness of the Colorado Plateau are the large number of sites within it that have been set aside for preservation. There are nine National Parks (including Grand Canyon, Zion, Arches, Canyonlands, Bryce Canyon and Mesa Verde) and eighteen National Monuments (including Bear’s Ears, Dinosaur, Chaco Canyon, Natural Bridges and Canyon of the Ancients) within the boundaries of the Colorado Plateau. There are more “national” designation sites on the Colorado Plateau than in any other place in the country outside of Washington, D.C..

Landscape Arch in Arches National Park. Photo by M. Fischer

Arches National Park sits on top of a very active part of the underlying salt bed. Its surface sandstone layers have been extensively moved about and cracked by deep shifts in the salt. This has generated many sets of fins that then have been spectacularly eroded. A good place to see fins up-close in the park is at the start of the Landscape Arch trail. As the trail leaves the parking area it runs between two tall, relatively intact, Entrada sandstone fins. The trail space between the fins is shady and cool and the facing rocks are extensively covered with lichens.

If you look back after walking through the gap between these fins, you can see that one side of each fin (the northeast) is slightly concave while the other (the southwest) is flat or, in places, even slightly bowed outward. Water, and snow and ice have started to work on the northeast faces of the fins scratching away the stone’s sand grains. On the more sheltered side of the fin, though, this erosion has occurred more slowly if at all.

Delicate Arch in Arches national Park. Photo by J. Hamilton

This gentle wearing away of the exposed face of a fin will eventually work its way deeper and deeper into the sandstone face. Shallow holes are formed which, as they pool more water and hold more and more ice, then begin to erode more rapidly. Small pits expand into deeper holes and then, after a great span of time, a hole might even extend all the way through to the other face of the fin making a “window.” These windows then expand and, if the rock is strong enough, a bridge or an arch may result. If the rock is not strong enough, the whole rock fin collapses into a pile of sand and stony debris. Even if the rock is strong, though, the bridge or arch is a temporary thing and will, eventually, collapse into a pile of debris. Erosion always wins!

Photo by M. Fischer

The number and diversity of arches, bridges and windows across the terrain of Arches National Park is unmatched by any other place in the world. There are, according to the National Park Service, over 2000 cataloged arches in the park! The landscape is unique, dream-like and unforgettable. The underlying salt bed must have been incredibly active to generate all of the cracks in the overlying sandstone. The sand grains in the fin sandstones, in turn, must have been lightly held together to allow the extensive erosion of the stone that then generated the incredible number of holes and windows visible across Arches. The innate strength of these eroding rocks, though, to then hold the crumbling stone together in fragile arches and bridges must have been a uniquely balanced set of innate characteristics. Arches National Park is like no other place on Earth.

Photo by J. Hamilton

In 1956 and 1957, Edward Abby worked as a park ranger at Arches National Monument (which became Arches National Park in 1971). He wrote about some of his experiences in and around Arches in his 1968 book Desert Solitaire. Here are two passages about arches:

“There are incredibly pious Midwesterners who climb a mile and a half under the desert sun to view Delicate Arch and find only God, and the equally inevitable student of geology who look at the arch and see only Lyell and the uniformity of nature. You may find proof for or against His existence. Suit yourself.’

“If Delicate Arch has any significance it lies, I will venture, in the power of the odd and unexpected to startle the senses and surprise the mind out of ruts of habit, to compel us into a reawakened awareness of the wonderful – that which is full of wonder,”      

I have a notebook full of quotes from Desert Solitaire. It is one of my favorite books. I highly recommend it!

We spent two days hiking in Arches and saw sculpted and molded masses of rock that defied our imaginations! It was wonderful, truly a place full of wonder!

(Next week: sagebrush!)

Rock Arches in Arches National Park, Photo by M. Fischer

(Click on the following link to listen to an audio version of this blog … Drive to Utah

The first weekend in May, Deborah and I left Greeley and drove an hour south and east to the Denver Airport. Our son and daughter-in-law arrived on-time from Seattle, and we scooped them up in the cave-like arrival area of the airport and then blasted back out into the sunshine. We headed west on the freeway and started our trip to Moab, Utah.

This drive to Moab from Denver goes across some great extremes in physical landscapes: the Denver airport is on the western edge of the High Plains. Its surrounding, dry, sandy terrain is as flat, and as hypnotically monotonous as can be imagined. The original vegetation of scattered sagebrush and juniper has been mostly replaced with irrigated agricultural fields, and many of those fields have, in turn, been more recently replaced by clusters of condominiums and cookie-cutter McMansions. People are filling all of the open spaces around here!

The Interstate (I-70) drops down a little bit from the edge of the Plains and crosses the densely people-packed, rolling terrain of the Colorado Piedmont. Blocks of warehouses and expanses of oil and gas refineries and storage tanks are separated by clustered nodes of fast food restaurants and gas stations. The traffic is tightly packed and going by insanely rapidly! Finally, the Interstate rises into the equally people-packed foothills of the Rocky Mountains and then starts to climb up an exploding, exponential altitude curve as it goes up the east face of the middle section of the Rocky Mountains.

Photo by Bidgee, Wikimedia Commons

The mountains!! Flashes of slopes covered with trees race by as you drive on at speeds once thought to be instantly fatal for human beings! In the early 19^th Century, “experts” cautioned people against riding on trains at 25 or 30 mph! The unnatural speed, they contended, would cause irreparable damage to your brain and, probably, stop your heart! What would those experts say about racing along in tiny, mostly plastic boxes, at 75 mph? What would they even say about plastic?

My guess is that most of the blurred, passing trees outside my car windows are lodgepole pines, but I know that there are also mixes and patches of spruce, fir and some other pine species all along the way. Dense stands of aspens that vary in size from a few dozen to several hundred trees, are just leafing out and are glowing softly green above their white-barked trunks. The aspen clusters are surrounded  by the incredibly numerous pines. Unfortunately, most of those the pines are gray, needless, and dead or dying.

The on-going pine tree apocalypse is all around us. As I wrote in Signs of Spring 11 (May 13, 2021):

In Colorado alone 70% of the state’s 1.7 million acres of lodgepole pines have been damaged or destroyed by mountain pine beetles (MPB’s). MPB’s in Colorado are estimated to have killed a total of 3.4 million acres of pines! One in fourteen of all of the trees in the state are dead primarily from the activity of MPB’s! Standing, dead trees in Colorado forests have increased 30% since 2010 to a total of 814 million trees.

Driving over the Rockies on I-70 is like watching this pine tree extinction roll by on HD-TV!

We  cross the Continental Divide at Loveland Pass through the Eisenhower Tunnel (elevation11,158’). When this tunnel was completed (first tube opened in 1973 and the second tube in 1979) it was the highest tunnel in the world and remains to this day the highest point in the Interstate Highway System and also the system’s longest mountain tunnel (1.7 miles).

Vail from I-70. Photo by S, Martin, Flickr

From the tunnel we head on to Vail Pass.  High fences are visible along the sides of the highway. These fences are designed to prevent (or, at least, inhibit) animal access to the Interstate. The Vail Pass section of I-70 crosses through the Eagles Nest Wilderness area which is part of the White River National Forest. There is abundant wildlife in this region including mule deer, elk, moose, black bear, mountain lions and even a breeding population of Canada lynx! The fences attempt to direct wildlife to safer crossings via underpasses. Currently, three more wildlife crossing passages (the “Vail Pass Wildlife Byway” project) are being proposed to insure the continuity of and safe passage between the rich wildlife habitats on both sides of the Interstate.

Driving through the Vail Pass, we see skiers still using the slopes at Copper Mountain. The snow, though, is visibly thinning and becoming discontinuous on the mountainsides. When we return on our return leg (May 14) there are no skiers on the mountain.

We stop in Vail to have lunch. We got some delicious sandwiches in the nearly deserted town. The cobblestones and winding streets are obviously intended to resemble some small ski village in the Alps. We pick up a realtor guide to look at while we eat. The small, three-bedroom condo for only $7 million dollars stands out as a bargain that is hard to pass up!

Photo by S. Skrzydio, Wikimedia Commons

While we eat at our outside, patio table, five, black-billed magpies perch on the patio railing and closely watch us. Two crows eventually join them. The magpies take turns hopping over to the left-over plates on the table next to ours. They very specifically grab hunks of cheese out of the half-eaten salads. They are very orderly, but the magpies have obviously explained to the crows that they are not to join in on the smorgasbord. I wonder why there are crows here instead of ravens? At this altitude, I would have thought that ravens would have replaced crows. I bet the magpies would have to stand aside if there were hungry ravens about!

The final, mountain section of I-70 is one of the most spectacular stretches of road I have ever seen! If my father (a civil engineer) had been with us, I am sure

I-70 through Glen Canyon. Photo by P. Pelster, Wikimedia Commons

that he would have gone on and on about the brilliance of the engineering that made the highway’s passage through the narrow slot of Glenwood Canyon possible: the tunnels, the viaducts and the cantilevered roadways! As it was, though, I just soaked in the unbelievable scenery and heart-stopping vistas!

It is important to note that “Glenwood Canyon” here on the Colorado River in western Colorado is not “Glen Canyon.” Glen Canyon is further downstream, although also on the Colorado River, in southeastern and southcentral Utah.  Glen Canyon was the site of a large dam (the Glen Canyon Dam) that was constructed in the early 1960’s.

The dam flooded Glen Canyon and created the huge reservoir called Lake Powell. Edward Abby, in his book Desert Solitaire,  wrote about a float trip he and a companion made through Glen Canyon before the flooding. His vivid descriptions of the canyon and all of its natural and archeological wonders easily made the case that the loss of Glen Canyon was a crime both against Nature and Humanity! Also, the ongoing, rapid evaporation of Lake Powell in these recent decades of extreme drought only makes the dam and the loss of the canyon seem all that more pointless!

Driving out of the mountains we enter a new physiographic region: the Colorado Plateau! And, through the haze of a raging dust storm, we get glimpses of the red, layered sandstones that we’ve driven so far to see!

(Next: the Colorado Plateau!)

Photo by D. Sillman

(Click on the link to listen to an audio version of this blog … Bird and windows part 2

Last week we started a discussion of why birds fly into window glass. We outlined the scope of the problem, talked about some bird ocular biology and began to enumerate some of the aspects of building locations and features of windows that contribute to bird/glass collisions. This week we’ll continue to discuss the features of windows that contribute to increased collisions and then talk about some possible solutions to this very significant problem!

The nature of the window glass itself has an impact on bird/glass collisions. Reflective glass is much more likely to lead to bird strikes than clear glass especially if there is vegetation around the window that is being reflected in the glass panes. Interestingly, very few bird collisions with windows are attributed to birds attempting to “fly through” the window glass, although visible house plants on the inside of a clear window can lead to increased numbers of bird/glass collisions.

Photo by Teipangshan102, Wikimedia Commons

Heights of the windows influences the probability of bird/glass collisions. Large windows at ground level and large windows ten feet or more above the ground have increased numbers of bird strikes compared to smaller windows or windows located at intermediate heights from the ground.

The time of year affects the number of and the nature of bird strikes: in winter, birds feeding at bird feeders near windows are most likely to strike the window panes. In spring and fall, non-resident (migratory) birds are most likely to strike windows. Interestingly, in the summer window strikes are relatively uncommon possibly due to the decreased ranges over which most birds move during their nesting and breeding season.

The time of day affects the number of bird/glass collisions. Most bird strikes occur in the morning unless other factors (like bird flocks flying from feeder to feeder or yard to yard) influence the movement of the birds.

There seems to be no particular selection process occurring when birds strike window glass or any particular type of learning going on. In most window strike studies there is no pattern of age or gender in the strike (although one study did report that in a particular area, juvenal individuals of the most abundant bird species were involved in most of the window strikes while in the less abundant bird species, adults were involved in most of the window strikes). Since the damage caused by the window strike is typically severe and overwhelmingly fatal, there is no opportunity for learning to occur that might lead to the birds modifying their flight behaviors around the glass panes.

Photo by Jiuguang Wang, Wikimedia Commons

Light may or may not influence window strikes. Few bird strikes occur in lighted windows at night. The most likely explanation for this, though, is that very few birds are out flying around at night. Migrating flocks of birds, though, do fly at night and can be attracted to the bright lights of cities. Many migrating flocks fly at such high altitudes that ground lights do not influence them, but at dusk and dawn when the flocks are taking off or landin or on nights with a low cloud cover or adverse weather conditions, migrating flocks fly at lower altitudes. These lower flying birds may be able to see the lights of cities and the illuminated windows of urban buildings. Under these conditions the urban light sources may be both an unwanted attractant and a bewildering and disorienting force for the birds that may lead to their exhaustion or to fatal window and/or building collisions. A number of North American cities have established “Lights Out” programs during peak bird migration periods. These programs seem to have been effective in reducing the influence of urban lights on the passing, migratory flocks.

Photo by Window Gem, ETSY

Silhouettes affixed to windows (often silhouettes of large birds like hawks) are not effective in preventing bird/window collisions.  Putting the silhouettes on the inside panes of the windows, in particular, completely hides the image from the visual field of the birds (they are only able to see the outermost side of a pane of glass in a window). Even placing large images on the outside pane of the glass windows does very little to prevent window collisions unless the pattern density of the images is sufficiently close together to guarantee perception by the birds.

Some very elegant experiments have shown that birds can see a window pane only if the outer glass surface of the window has a dense pattern of lines or shapes covering all of its surface area. A rule has been coined to describe these patterns:  the “2 X 4 Rule.”

The “2 X 4 Rule” basically states that the outer glass pane of a window must be completely covered with either thin (a minimum of 2 mm wide) horizontal lines that are two inches apart or similarly thin (again a minimum of 2 mm wide) vertical lines that are four inches apart. These patterns generate a grid that birds can see and can act to prevent 90% of bird/glass collisions.

Photo by Duncraft

The lines or dots in the 2 X 4 grid can be painted on the window, or they can be threads or strings or they can be special plastic strips that are UV reflective! These UV reflective strips have a great advantage over the other types of window pattern generators in that they are not visible by humans! Thin painted or threaded lines in either of the 2 X 4 grids only block 7% of the windows surface, but the UV reflective strips block 0%! Several companies are currently manufacturing windows that have built in UV strips, and one plastic manufacturer has developed a process to make clear sheets of plastic with UV reflective designs that can be affixed to the outer glass pane of a window.

There are other ways to make an existing window bird collision proof. A window can be covered with an outside sunshade or louvre to prevent birds from striking the invisible glass. A window could also be covered by a layer of screening or fine netting. This covering would both satisfy the 2 X 4 Rule and make the window visible to birds and also, if it was set up to have a space between the screen and the window glass, would allow the birds to strike a soft, giving surface if they did fly into it and not experience the catastrophic damage from a hard surface collision. Advocates of these screens describe them as “bird trampolines!”

Photo by D. Sillman

Several years ago, I built a sunroom on the west side of my house back in Pennsylvania. The sunroom was built over the site of a former wooden deck. There had been before the construction of the sunroom and continued to be after the construction of the sunroom, bird feeders approximately 15 feet away from the western-most edge of the deck and sunroom. “New glass,” as I indicated before, is often quite deadly to birds who have established flight patterns through an area. The glass of the sunroom, though, was UV reflective, and I hoped that it would be visible to the surrounding birds. Over the two years we lived in the PA house with the sunroom we only had two or three bird/window collisions, a surprisingly low number considering the nearby attractants (both bird feeders and bird baths) and the size and height from ground level of the windows. My hypothesis is that the UV reflective nature of the glass helped to make the glass panes visible to the birds! There have been a number of experiments that have tested the hypothesis that UV reflective glass would reduce bird/glass collisions, but the results of these studies have not been consistent. My experience, though, indicates that it might be another type of solution to this very serious problem.

Photo by Pixabay

(Click on the link to listen to an audio version of this blog … Bird and windows part 1

A 2019 study estimated that there are 7.2 billion birds in the United States and Canada. This is a large number, but it is significantly less than the 10.1 billion birds that were estimated to live in the United States and Canada just 50 years ago. Much of the decline in our avian populations is due to habitat loss, but two other, on-going factors (bird predation by cats and bird collisions with windows) may be steadily eroding bird populations and preventing many species from reestablishing their former population densities. These two factors are not at all trivial. Every year 2.6 billion birds killed by domestic cats in the United States alone, and over a billion birds each year in the United States die from collisions with windows.

The Audubon Society strongly recommends keeping cats indoors to try to reduce the carnage from their predatory habits. Even an over-fed, over-weight, lumbering house cat can do a great of damage to birds feeding or nesting on or near the ground! The window collision problem, though, is more complicated and does not have such an obvious solution.

Window after bird collision. Photo by Anguskirk, Flickr

When birds fly into windows the result is usually awful. A bird in flight “leads with its head,” and it is its head that typically slams directly into the window and bears the brunt of the damage from the force of collision. Necropsies of window-killed birds have shown that fractures of vertebrae or parts of the appendicular skeleton are much less common than severe soft tissue damage to the brain. A bird may be killed outright in its collision with a window or it may only be just momentarily knocked unconscious and seemingly “recover” enough to fly away. Often, though, that “stunned” bird has sustained such severe brain damage that it either dies soon after from its injuries or is unable to function to feed itself or avoid predators (like the omnipresent house cats!) and, thus, succumbs soon after.

Why do birds fly into windows?

Photo by Pixabay

The simplest answer to this question, and, possibly, the most accurate answer, is that birds simply don’t see the window glass. Birds do have wonderfully complex eyes, and, we infer, that using those complex eyes they generate very detailed and very precise visual fields. Bird eyes are larger relative to their body size than human eyes and have more kinds of “detail” photoreceptors (“cones”) on their retinas than humans. In addition to the blue, green and red cones that are seen in humans, birds also have cones that are sensitive to UV wavelengths! Further, birds have multiple areas on their retinas where these cones are concentrated to form very precise visual reception systems. Humans, on the other hand, only have a single cone-concentrated, high visual acuity area (the “fovea centralis”).

Also, in contrast to the cone structures of human retinas,  many of the cones in bird retinas are paired together and most have tiny oil droplets that act as light filters. This filtration enables avian cones to be even more specific as to the particular wavelength of light that stimulates them. This gives birds a significantly more precisely tuned visual system than what is present in humans. But, they still can’t see window glass!

People often have trouble seeing glass windows and doors, too. I had a student a number of years ago on a field trip to Greece walk right into a glass door. She broke her nose and was very uncomfortable from the injury, but, at least, she had a tough enough cranium to avoid serious internal injuries!

Birds of North America

The total number of bird species on Earth depends on how finely you separate and distinguish species from subspecies and varieties (see Signs of Winter 1, December 16, 2021 and Signs of Winter 2, December 23, 2021 for a discussion of this species definition dilemma), but most estimates range from 10,000 to 20,000 species. Out of this diverse array of birds just under 1400 species are known to strike windows.

Why do such a small percentage of bird species strike windows, and why do these specific species of birds do so in very significant numbers?

The most obvious way to answer these questions is by recognizing that most of the diverse array of bird species do not live near people! Commonsense inferences are often quite misleading in science, but this one is incredibly accurate and insightful if not just a bit silly because it is so obvious: only birds that live near windows can fly into window glass! And, a useful corollary to this rule might be, those species that are most abundant near human habitations (and their windows) will be those species that most often strike windows and subsequently die from these collisions!

Photo by Pixabay

A study published in 2012 in the journal Wildlife Research by researchers at the University of Alberta outlined an order of observed bird/window strikes in an array of types of human habitations. The greatest number of strikes were seen in rural houses that had bird feeders while the second greatest number of window strikes were seen in rural houses without bird feeders. These observations reflect the greater number of birds in non-urban habitats and the “common sense’ rule outlined in the paragraph above, “where there are a lot of birds near windows, there will be a lot of collisions.”

Public Domain

The third greatest number of window collisions observed in this study occurred in urban houses with bird feeders, and the fourth greatest number of collisions observed occurred in urban houses without bird feeders.  Finally, the smallest number of window collisions occurred in apartment buildings. These observations fit our “common sense” rule governing bird/window interactions.

What other factors besides simple abundance of birds near windows affects the number of window strikes?

The nature of the surrounding landscape can have an influence. Trees and shrubs near windows lead to more strikes. Bird feeders or bird baths (or other water sources) near windows lead to more strikes. Fruit bearing vegetation near a window lead to more strikes. Sheltered perches (favored by birds) near a window lead to more strikes. Interestingly, though, there is a very non-intuitive relationship between the distance the attractant is to the window and the probability of birds striking the glass. Any attractant that is three feet or less from the window does not lead to increased bird/window strikes, and any attractant that is more that three feet away from the window (even those that were ten feet or even twenty feet or more away) does lead to increased bird/window strikes!

The explanation for these observations involves how quickly a bird can go from a resting state to a flying velocity that generates sufficient momentum to cause significant brain damage in a window collision. Three feet, apparently, is too short a distance to allow fatal velocities and momentums to be achieved.

Supporting this momentum-strike hypothesis is the observation that slow flying birds (or at, least, birds whose initial flight velocities are fairly slow) are less likely to be killed in window strikes than more rapidly flying birds. These “slow” birds include rock pigeons, European starlings and house sparrows (and these last two species are in the very exclusive “one billion club.” Their huge worldwide populations may be maintaining themselves, at least in part, because of their relative immunity to window strike fatalities).

Photo by D. Sillman

The relative location of the window glass (on the north, south, east or west of a house or building) does not seem to have a significant impact on the probability of a bird/glass strike. However, the history of a window’s location may have an impact. When a new house or building with windows is constructed, there can be a period of time over which a large number of bird/glass strikes occur. This is often due to non-resident birds, who have historically flown through a particular area, violently and unexpectedly encountering one of the new panes of glass. As these bird flocks “age out” (or die from fatal window strikes) these collisions become less and less frequent.

The density of building development has an impact on the probability of bird/window collisions. Buildings or houses that are closer together have fewer bird/window collisions. Houses in older neighborhoods tend to have more bird/window collisions probably because of the increased density of vegetation that typically surrounds older homes.

(Next week, we’ll continue this discussion and then describe some possible solutions to this problem!)

Photo from PIxabay

(Click on this link to listen to an audio version of this blog …Active grandparent hypothesis

There is no doubt that physical activity (i.e. “exercise”) is good for your health. This is true throughout life but seems to be particularly important as we get older. Many studies have shown that maintaining high levels of physical activity helps us to stave off cardiovascular disease, cancer, diabetes and other, sometimes acutely fatal, disorders and also many other chronically debilitating conditions including dementia. I have talked about some of the research into the effects of exercise on mental functions (Signs of Fall 7, October 14, 2021) and its influence in preventing and speeding the recovery from cancer (Signs of Fall 8, October 7, 2021). Exercise can be an activity, to quote Dr. Daniel Lieberman, an evolutionary biologist who has studied the importance of running in human evolution, that ensures that “the span of our good health matches the span of our lives.”

Why is exercise (i.e. being active) so important to our health? This was the essential question asked in a recent article in the New York Times (February 2, 2022) that discussed the “active grandparent hypothesis.” This hypothesis basically states that the long, post-reproductive span of years seen in human beings was evolutionarily selected for because the presence of grandparents assisting in the care and rearing of their children’s children increased the survival rates of those children (i.e. increased their evolutionary “fitness”). As I read this article it occurred to me that something was being left out in this discussion, or that maybe the pieces of the discussion were being arranged in the wrong order.

Let’s start from the beginning and see where we end up.

iKung bushmen. Photo by I. Sewell, Wikimedia Commons

It is quite possible that activity is woven into our very essence of being human! Humans were initially hunter-gatherers. Hunting and gathering requires a great deal of physical energy and activity, so the individual humans who were most active would, logically, hunt and gather the most food. Adaptations for increased activity included musculoskeletal changes (which we can see in the fossil record), cardiovascular changes, respiratory changes and thermoregulatory changes (which we can infer from how our organ systems work compared to those systems of other primates).

There also had to be, though, more subtle changes to our bodies: changes to our “rest and repair” metabolic systems that would not only heal our bodies from the damage from all of our stressful activity but also continuously reshape and reconfigure our tissues and organs to keep our bodies at peak health. This is the key point that is not mentioned in most evolutionary discussions of the influence of exercise or its impact on longevity! Why do we live so long? Maybe it is because our bodies, in response to stress, continually remake themselves!

(I had an orthopedics professor back in medical school who said that body parts are more likely to “rust out” than “wear out!” I think that he intuitively grasped this essential evolutionary idea of the need for and benefit of activity and repair!)

Photo by M. Fischer

There is an idea in evolutionary psychology that humans are adapted to find as many opportunities as possible to rest and to use as little energy as possible to accomplish a task (personal comment from Dr. M. I. Hamilton). At a first glance this idea might seem to contradict the idea that humans are evolutionarily adapted to being very physically active. This “quest for rest” looks, in fact, like an adaptation for laziness, but these two seemingly contrary ideas may actually compliment each other. Maybe looking for opportunities to rest and being careful with energy outputs help us to recover from the stress of the necessarily, high energy physical and maybe even mental activities of life!

I think that this cluster of metabolic and behavioral changes (all shaped by natural selection) are the key to understanding why we get so much benefit from exercise and maybe why humans have evolved to have such long life spans! It also may explain why, if we ignore the necessity for rest, we put our bodies and our minds under remarkable strain. Natural selection favored not only the individuals who could run the fastest and jump the highest, but also the ones who could recover the most efficiently from all of the wear and tear that activity causes!

Photo by A. MIlls, Pixnio

Think about it: modern life so emphasizes mental activity over physical that we have had to invent and seek out substitutes for those activities that our bodies are adapted to and require to stay healthy. So, we exercise: we run away from nothing in particular chasing after nothing at all. We expend large amounts of energy lifting weights up and down with no real accomplishment or outcome. We jump around, we dance, we pedal, we kick out our arms and legs for no real purpose. We use our very functional muscles over and over again and accomplish nothing other than the use of those muscles!

We also realize that without proper rest our bodies and minds will begin to function less efficiently. Much of the stress, anxiety and mental disabilities that beset modern humans are best dealt with via programs that focus our attention out of our immediate experiences.  After all, what is meditation or “mindfulness” other than focused rest?

So, back to those early hunter-gathers: when children were born to these evolving humans, the children who were better fed and more closely cared for were more likely to survive and, eventually, reproduce. The children of the most active, most efficiently repairing parents would not only get more food but also would inherit the set of genes that generated the more physically active, self-repairing adult. And this dynamic cycle would go on and on generating humans that were by nature and by necessity increasingly physically active and increasingly able to repair themselves.

There are, however, limits to this parent-child food and care cycle and, interestingly, a factor that could further stretch this resource acquisition dynamic just might be a tie-in to the evolving human rest-and-repair metabolic evolution.

Photo by M. Hamilton

If a group of humans had multiple adults (adults in addition to the parents) that could provide for and care for the children, then those children would be increasingly likely to survive and pass their genes on to the next generation. Further, if Richard Dawkins’ “selfish gene” hypothesis is valid, the additional adults that would best satisfy the mysterious forces of evolutionary compulsion would be ones who shared a significant percentage of their genes with those children. Grown-up siblings or uncles and aunts would also have been good possibilities to serve as child-rearing-assistors, but they may have been deep into their own reproductive efforts and have little time or energy to assist their brothers and sisters or nieces and nephews. Grandparents, though, individuals past their own reproductive years who are living longer because of their activity- stimulated metabolic repair systems, might be even better choices.

Photo by D. Sillman

This is the essence of the “active grandparent hypothesis” (a set of ideas that were formerly, and maybe evolutionarily more appropriately if not as politically correctly, called the “grandmother hypothesis”): if adults that have aged past their reproductive years could stay active and healthy, they would be very useful in sustaining and rearing their children’s children or maybe even their children’s children’s children! It is possible that the long span of our post-reproductive lives, which is a consequence of our activity/self-repair metabolic adaptations, was additionally selected for by the benefit that these years convey on our offspring’s offspring!

I have talked about the grandmother hypothesis before (Signs of Summer 1, June 4, 2020). Young orcas in pods (especially young females) have an increased  rate of survival if the mother of their mother is still living in the pod. These “grandmother” orcas provide food for the young whales and maybe even protection. The ecological cost of providing for a non-reproductive individual in pod is more than compensated for by the overall benefit to the young whales.

Photo by L. Drake

Complicated! Let’s make it simple. Exercise because your body needs to be continually stressed, repaired and rebuilt (your genes demand it!). Don’t work all of the time (your genes also demand rest!). Give in to some bouts of idleness, structure some down-time with contemplation of literature, art, playtime with your pets, meditation or some other mindful-like activities,

Enjoy your long life! Play with your grandchildren (and give them lots of ice cream and cookies!! (oh, yeah… fruit and vegetables, too!)).

Photo by D. Sillman

(Click on this link to listen to an audio version of this blog … Backyard Fox Squirrels

I have a backyard full of fox squirrels that are great fun to watch. I have written about them several times in my emails and blogs (see Signs of Summer 15, September 10, 2020). We started out with just two squirrels in the yard, but, through the winter, that increased to seven or eight. If you feed them, they will multiply!

I have been very impressed by a number of aspects of fox squirrel behavior: first and foremost, they are incredibly tough and venture out on even the coldest winter day. They do, however, hate the snow! I watched one fox squirrel, clinging to the trunk of our honey locust tree, take a half an hour to get his nerve up to dive into the ten inches of fresh snow that covered the ten feet or so of open yard between him and the sunflower seed feeder. His first plunge buried him so deeply that only the tip of his tail was visible. He then leaped back into the tree and took two more “snow-dives” before he made it all the way to the feeder.

In the snow the fox squirrels are very attentive to their paws. They often run a few steps and then rub their front paws furiously against their chests and shake their back paws vigorously against their sides before they move any further. I wonder if their paws freeze or if they accumulate irritating crusts of ice or snow?

I have watched the squirrels trim off and consume honey locust seeds and hang precariously from extremely thin end-branches to reach clusters of ripe pods. I have watched them do the same up on the much higher branches of the ponderosa pines in order to reach mature pine cones.

Photo by D. Sillman

In the winter and spring, the squirrels shinny out to the very ends of the branches of the honey locust tree and very intently chew on something. Leaf and/or flower buds? I watched my Pennsylvania gray squirrels do this on my backyard red maple trees, too. The only part of the branches of those maples that grew leaves in the spring and summer were the branch sections too slender to support a squirrel!

This leaf trimming by the squirrels could be energetically beneficial to a tree. The very end branches of the limb sections are those guaranteed to get maximum sunlight. The leaves located  more in the center of the tree crown (those on the thicker, inner branches that easily reached by the bud-eating squirrels) would be quite shaded. Those sun-lit, end-leaves, then, would be most productive in fixing energy. Trimming out the potentially less productive (but equally expensive to make!) inner leaves would allow the tree allocate its leaf making energy in a more efficient manner!

I have also been very impressed by how polite and tolerant the fox squirrels are to each other and how little intra-specific, physical aggression they display. The literature indicates that they are not a very territorial species, and compared to their cousin, the gray squirrel (whom I observed extensively back in Pennsylvania), they almost placidly accept the presence of each other in the yard. Possibly the abundance of food (sunflower seeds, locust seeds and pine seeds) explains the apparent lack of overt competitive behaviors). The only “arguments” I have observed between fox squirrel individuals in the yard have been over access to the sunflower feeder! Fights over junk food, as most of us who have ever had college roommates know, are not at all uncommon!

Photo by D. Sillman

I have also watched the fox squirrels go up and down the streets of our neighborhood looking for other foods (like black walnuts and planetree seed pods). I have not found the neighborhood black walnut tree, but I did locate the London planetree in the front yard of one of my neighbor’s about a block away. It is a long way to run to get these seed balls and necessitates the crossing of two streets. They must be an important resource.

At first the fox squirrels ignored the bird bath I had set up on the back patio. I speculated that they were “desert-adapted” out here on the dry plains of Colorado and might not know what liquid water was! Maybe they generated all of the their water requirements from their food? This winter, though, several of the squirrels have started to climb up into the bird bath to get drinks of water!

When we moved into our Greeley house a year and a half ago, our next-door neighbor pointed out a fox squirrel that only had one eye. The neighbor thought that a hawk had injured him during a failed hunt and grab. The one-eyed squirrel seemed to move pretty well for someone without any depth perception. Not being able to see potential predators on one whole side of your body was probably a difficulty, too. The one-eyed squirrel was around all last summer, but sometime in the fall, he disappeared. Another hawk? A car accident out on the street? A missed jump up in the ponderosa pine? Something happened.

Public Domain

Last December, I mentioned seeing a small squirrel with a very short tail. She was a very distinctive individual because of her tail and was easily recognized. I named her “Stubbs.” She is the only backyard squirrel that has a name! When Stubbs first showed up she always entered the yard very furtively and was quite jumpy and cautious around the larger squirrels. At first I thought that she was a different species (a pine squirrel or chickaree), but as I have watched her over the year, I have come to the conclusion that she is a fox squirrel who, last December, must have been the runt of a summer litter. She has since grown considerably (but still has a tail that is only 1/3 to ½ the length of a normal fox squirrel.

My grandson, Ari, loves Stubbs! He gets so excited when we see her in the backyard that he often goes running through the house to find Deborah or his mother or father yelling “it’s Stubbs, it’s Stubbs! Come and see!”

Stubbs feeds at different times from the other squirrels. She is often in the sunflower seed feeder right at dusk when all of the other squirrels have retreated to their leaf nests for the night. She is also often at the feeder during the mid-day hiatus and siesta for the other squirrels. My guess is that her tail was injured very early in her life possibly by another squirrel. Maybe her small size and then her oddly cropped tail made her a target for abuse? Maybe fox squirrels are not so placid as I have hypothesized.

Photo by J. Quinn, Wikimedia Commons

I had assumed that they only impediment that Stubbs’ short tail might cause is the absence of a warm covering wrap at night, but then a couple of months ago I noticed something else: Izzy and I went out in the backyard mid-morning. Our arrival scattered the squirrels who ran up the locust and pine trees and out across the tops of tall wooden fence that surrounds the yard. Three squirrels (including Stubbs) ran along the narrow fence top. The two, normal-tailed squirrels raced easily down the fence. Stubbs, though, stumbled every few feet and had to catch herself to keep from falling. The two normal-tailed squirrels easily out raced Stubbs to the cover of the backyard cedar tree.

I think that possibly Stubbs was not able to use her short tail to help her keep her balance on the fence top.  Therefore, she stumbled and moved more slowly than her more normally-tailed companions. Running from Izzy and I, this slower escape would not matter, but if the escape was from a real predator, Stubbs would end up as some hawk’s or dog’s or even owl’s meal (Stubbs’ pattern of feeding at dusk just might overlap with the start of our neighborhood’s great horned owl’s hunting time)!

Photo by D. Sillman

In early March, I noticed that the number of squirrels in my yard had decreased by three. There were now just four squirrels racing up an down the locust tree and gorging themselves at the sunflower seed feeder. One of the missing squirrels, sadly, was Stubbs! My hope is that the yearling squirrels got pushed out of the backyard territory to make room for this spring’s litter. Maybe Stubbs is living down the block with some of her siblings. I will keep my eyes open for her short, stubby tail!

Public Domain

(Click on this link to listen to an audio version of this blog … Ponderosa pines

The ponderosa pine (Pinus ponderosa) is the most widely distributed pine in North America. It is found from southern Canada down to Mexico, and from the Pacific coast to the Dakotas and the western edges of Nebraska and Oklahoma. It has three geographic varieties: 1. The Pacific ponderosa pine (P. ponderosa var. ponderosa) which grows on the west coast from British Columbia down to near San Diego and over the Continental Divide into Montana and Idaho. 2. The Rocky Mountain (or “Interior”) ponderosa pine (P. ponderosa var scopulorum) which grows in discontinuous populations on isolated mountains and plateaus across Montana into the Dakotas, south across eastern Wyoming and then down into and over the Rocky Mountains in Colorado and New Mexico. And, 3. The Arizona ponderosa pine (P. ponderosa var arizona) which grows primarily in south-eastern Arizona.

The absence of the Interior variety of this tree from large areas east of the Continental Divide is thought to be due to a synergy between two key limiting factors for the species. Growth of very young seedlings requires moisture, and many areas within this potential growth region do not receive predictably significant moisture during the ponderosa pine’s critical seedling growth period (early spring or early summer). Also, the combination of high latitude and high altitude can so compress the length of the potential growing season, that the ponderosa pine is not able to reliably establish itself. It just doesn’t have sufficient time to grow in these truncated, summer-seasonal locations. These two factors have generated the unusual patchwork distribution of the species especially in the northern-most part of its North American distribution.

Photo by R. N. Horne, Wikimedia Commons

Ponderosa pines grow on sites that receive between 11 and 69 inches of precipitation per year. The key to its existence on sites that are drier, as mentioned above, is, at the very least, there has to occasionally be some significant rainfall during the critical, early seedling growth time period. Once established (i.e. when seedlings are more than 100 days old) ponderosa pine seedlings are able to tolerate dry conditions because of their rapidly growing root systems, but for their first three months they are absolutely dependent on rainfall. This tree grows on many types of soils, but, in general, if annual rainfall is low, a more finely textured soil (which will more efficiently hold soil moisture and increase the effectiveness of precipitation) is preferred.

The ponderosa pine is a large tree (tallest recorded specimen was 232 feet tall and the largest recorded diameter at breast height was 8 1/2 feet. Average heights of these trees, though are between 60 and 150 feet). The ponderosa pine has distinctive bark that is black on young trees but yellow-brown and deeply and irregularly furrowed on older trees. Also, if you put your nose very close to one of the deep bark furrows of a ponderosa pine you can distinctly smell the scent of vanilla.

Ponderosa pines have long (5 to 10 inches) yellow-green needles that are clumped into fascicles of two (in the Pacific variety), or three (in the Interior variety) or five (in the Arizona variety). The needles also have a distinctive smell that is dominated by either a turpentine or a citrus scent. In Colorado, these distinctively long needles are a key visual identification feature for ponderosa pines.

Photo by K. Casper, Public Domain

Ponderosa pines are very shade intolerant. This results in many ponderosa pine stands growing as even-aged cohorts without significant seedling regeneration. Competition by other, often more rapidly growing tree species, though, can result in the exclusion of ponderosa pines from a site.

Once past their very delicate early seedling growth period, ponderosa pine seedlings, saplings, pole trees and mature trees are quite resistant to drought. They have extensive root systems with deep, anchoring tap roots and dense, shallow fibrous root systems that extend up to 150 feet around each tree.

Ponderosa pines have a complex relationship with fire. Seedlings are rapidly killed by even low intensity wildfires, but larger, older trees are protected from all but the most intense fires by their thick bark. Further, most of the ponderosa pine’s competing tree species are more sensitive to fire than it is, so fire tends to favor the persistence of ponderosa pines in pure stands. Fire suppression, though, has caused many of these competing species (like Douglas-firs and true firs) to persist and eventually shade out the shade-intolerant ponderosa pines.

Photo by D. Sillman

Ponderosa pines are valuable timber trees that are cut and harvested throughout North America. Often the removal of ponderosa pines leaves behind understory trees (like Douglas-fir, true fir and lodgepole pine) which then become the dominant species of the recovery forest. Natural regeneration of a ponderosa pine stand is a very sporadic occurrence requiring a nearly perfect synchrony of events: there must be an abundance of seed from a heavy seed/cone crop of the previous year that is matched with a sufficient quantity of rainfall for the critical early seedling growth period in the three months immediately after the cessation of freezing temperatures.

In the Rocky Mountains of Colorado ponderosa pine grows in pure stands and also in mixed forests with Rocky Mountain Douglas fir (Pseudotsuga menziesii, var. glauca) , blue spruce Picea pungens), lodgepole pine (Pinus contorta) , limber pine (Pinus flexilis) and quaking aspen (Populus tremuloides).

Male cones. Photo by T. De Gomez, Univ Arizona, Bugwood.org

Ponderosa pine is monoecious (i.e. there is only one type of individual). It bears clusters of small (1/2 inch long), cylindrical, yellow-red to purple, pollen producing (“male”) cones at the bases of its new growth branches and clusters of even smaller (1/4 inch long), egg-shaped, red to bluish, ovulate (“female”) cones near the end tips of these same, new growth branches. Pollen is released in late May to mid-June. The female cones take more than a year after pollination to mature (in August or September of the following year). The cones open on the tree and shed seeds through November. Seeds are shed very close to the parental tree unless the cones are clipped off of their branches and carried off by tree squirrels. I have found ponderosa pine cones from the four trees in my yard some distance down the street and have seen fox squirrels carrying cones along the ground and over the backyard utility wires.

Photo by C. Light, Wikimedia Commons

Each female cone contains about 70 seeds. These seeds are small and are eaten by a variety of birds, insects, chipmunks and tree squirrels. Normal seed production occurs every 2 or 3 years and heavy seed years occur every 8 years or so. Insects (especially the ponderosa pine cone beetle (Conophthorus ponderosaei) and ponderosa pine cone cone-worm (Diaryctria spp.)) damage about 30 to 60% of the seeds in the seed cones. Trees can produce seeds from 7 through 350 years of age. Peak seed production years are between ages 60 and 160 years.

Rabbits and hares and gophers kill seedlings. Browsing by deer, sheep and cattle may stunt trees, and trampling by these larger consumers may also kill seedlings and saplings. Over 100 species of insects are known to attack ponderosa pines including the mountain pine beetle (MPB) (Dendroctonous ponderosae) ( which also attacks lodgepole pines and limber pines). In Colorado 3 to 4 million pine trees (including 70% of the state’s lodgepole pines) have been killed by MPB’s (see Signs of Spring 11, May 13, 2021). Air pollution (especially ozone) damages ponderosa pine needles. There are also many root and bark diseases that affect this tree. Dwarf mistletoe is a frequently damaging epiphytic parasite which causes a 36% mortality in ponderosa pines in northern Arizona.

Photo by D. Sillman

Ponderosa pines have been planted extensively throughout my residential neighborhood here in Greeley. In my relatively small yard, I have four, 50+ foot tall, 18 to 20 inch dbh trees. There are also two stumps from ponderosa pines of a similar size that had been growing very close to the front wall of the house. The yard must have been for many decades a dense, ponderosa pine forest!

All of the intact, yard trees produce abundant cones which are harvested energetically by the local fox squirrels. I have even seen chickarees (“pine squirrels”) up in the trees’ cone-laden branches. The high branches of the ponderosa pine are used as hunting perches and day roosts by red-tailed hawks and great horned owls (although not at the same time, of course!). These trees are a critical, ecological cornerstone of my small, suburban ecosystem.

The ponderosa pine is tree # 32 on the West Campus section of the Campus Arboretum of the nearby University of Northern Colorado. These pines can grow in a wide variety of habitats and under a broad range of conditions as long as their critical, early-seedling stages are carefully nurtured and watered. They are iconic trees of the American West and the mountains!