Variation in Western Sparrow Hawks

The problem of what to call the sparrow hawks of various parts of the southwestern United States and northwestern Mexico has long been a puzzling one.Names employed in the past are Falco spat-vet&s spwverius, F. s. phaloena, F. s. deserticolus and F. s. penninsularis.Descriptions and ranges given by various authors (A.O.U.Check-list, 1910, 1931;Bergtold, 1927;Grinnell, 1914;van Rossem, 1931) have done violence to each other and have usually been of small assistance to the ornithologist who wishes to assign a name to a specimen with some assurance that it actually fits.In an effort to shed some light on the problem, I have carefully examined and measured 678 sparrow hawks, chiefly from western North America.About 7.5 additional specimens were examined casually, but are not included in this study because they were too worn or too young, or were molting too heavily to be measured, or because the data were incomplete.In addition, I have used, in one section of this paper, wing measurements of 49 specimens from British Columbia (37 from the Provincial Museum, 12 from the collection of Mr. Kenneth Racey).These measurements were taken for me by Dr. I. McT.Cowanto whom I offer my sincere thanks.The collections to which the specimens examined by me belong are shown in table 1.To all the owners and curators of these specimens I am extremely grateful for permission to study them and for other assistance.I am especially indebted to Dr. A. H. Miller of the Museum of Vertebrate Zoology in Berkeley and to A. J. van Rossem, Curator of the Dickey Collection in Los Angeles, not only for access to specimens in their care, but for many courtesies and' much assistance.