Recent Literature

Natural History and Differentiation in the Yellow-bellied Sapsucker.-ThomasR. Howell.Condor, 54 (5): 237-282, 7 figs., 1952.--Thefour generally recognized subspecies of Spkyrapicus varius constitute a fascinating example of arian evolution.Their complex relationships put to the test some of our modern criteria of species and subspecies.The ranges are almost wholly complementary: S. v. varius breeds across much of the northeastern United States and southern and western Canada; S. v. nuckalis is the bird of the Rocky Mountains, and ranges west to the Cascades; S. v. daggetti is confined principally to the Sierra Nevada, northern California, and adjacent areas; and S. v. tuber inhabits the Pacific Northwest.Most features of their life histories seem to be identical.Yet the migratory tendency is strongly developed in S. v. var•us, progressively less so in nucb.al•s and daggctt• respectively, and practically absent in tuber.Sexual dimorphism diminishes in a corresponding manner, disappearing altogether in tuber.The coloration varies so strikingly that the two western races, the "Red-breasted Sapsucker," have often been treated as a distinct species.More remarkable, in most of the limited areas where the breeding ranges of two races do come together, intermediates are far in the minority and interbreeding relatively uncommon.Only in the case of daggctti and tuber is a considerable zone of intergradation found.The author undertook as his doctoral thesis the investigation of this intensely interesting situation, by combined laboratory and field studies, placing special emphasis upon the critical point of the "breeding behavior of the races at the points of junction."His findings are most interestingly summarized in this paper, along with his conclusions concerning the present status and possible history of the several forms.Study of the pigmentation brings out the fact that the color differences, while probably genetic, are not as fundamental as they might first appear, the red carotenoid pigment being deposited chiefly at the tips of the feathers, and the red areas thus overlying to a large extent the black and white pattern beneath.But the characters are distinct enough to permit field recognition of the racial types and of intermediates, under favorable conditions even in juvenal plumage.The possibility of such recognition of living individuals enabled the author to make his greatest contribution: series of detailed nest observations in a number of selected areas of overlap.When Howell's original data are combined with the published records, and inferences made from the numbers and types of intermediates in collections, there are still wide gaps in our knowledge; but the picture of the interbreeding now becomes much clearer.Apparently there is considerable interbreeding where S. v. varius meets nuckalis (though this remains obscure), and where nuckalis meets daggetti; very little is to be found, however, in the areas where ruber comes east into central British Columbia to meet and separate the ranges of varius and nuckalis.The situation the author describes in some of these areas of contact is such that almost within a stone's throw may be found nesting pairs of each of two races, mixed pairs, and intermediates actually mated and raising young.A few miles to either side the breeding population, save for stray individuals, is made up exclusively of one race or the other.With such field data presented, and appropriately backed up by specimens, there can be little argument about the virtual allopatry or about the interfertility of these forms.The studies brought to light no differences in breeding behavior, and certain small variations in habitat preference are not always operative.By the widely accepted criteria here used, it is clear that the four populations can only be 218

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.