17 p. : 26 cm

The giant conebill, Oreomanes fraseri Sclater, 1860, is an endemic, monotypic genus of coerebid or thraupid-like bird distributed in the high Andes of South America from southern Colombia to southwestern Bolivia. This well-marked taxon appears to be restricted ecologically to 'islands' of woodland vegetation above timberline that are dominated by trees of the endemic Andean genus Polylepis (Rosaceae). The geographical distribution of Oreomanes fraseri is quite patchy. Oreomanes fraseri shows geographical variation in bill size and plumage color. Geographical variation, however, is very minor, and so it does not seem useful to describe it in terms of subspecies. The pattern of this variation is partly clinal amd partly checkerboard, as one would expect from the nature of the discontinuous distribution of the species. Range disjunctions and geographical isolation of populations do not appear conducive to incipient speciation. The patterns of geographical distribution and variation suggest either: (a) that the origin of the disjunctions is recent (i.e., there has not been enough time for the isolates to become morphologically and presumably also genetically differentiated); (b) the geographical isolation has been insufficient to promote differentiation (i.e., gene flow exists between isolated populations and counters the disrupting effects of geographical isolation); or (c) geographical isolation is effective and is relatively old in origin but the rate of morphological differentiation in the isolates is slow. Data are lacking at present to permit one to check which of these hypotheses is the most likely to explain the observed patterns

Title from caption

"January 30, 1984."

Includes bibliographical references (p. 15-17)

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