Canada 
Victoria Memorial Museum 
Bulletin No. 48 
BIOLOGICAL SERIES No. 13 
A STUDY OF BUTEO BOREALIS (GMELIN), THE RED-TAILED 
HAWK , AND ITS VARIETIES IN CANADA 
INTRODUCTION 
The exceeding variability of the Red-tailed Hawk has been a source 
of confusion and misunderstanding to systematic ornithologists. There 
are few common or generally distributed North American species of birds 
of which so little is known, or which have received so little critical attention. 
This has largely been due to lack of material, especially of breeding or 
summer birds, in collections. Most of the specimens available for exam- 
ination are migrant or winter birds, that offer no clear explanation of the 
relationship between the bewildering variety of characters they exhibit. 
Separation of individual from racial characters by the study of migrant 
material is practically impossible. 
Lately, however, considerable material has become available, and it 
seems that the time has come when a critical study of the species is advisable. 
This material consists of a large number of specimens composed mainly of 
breeding birds, in many cases in original, complete families, collected across 
the Dominion by the staff of the National Museum of Canada. Through 
the courtesy of the Museum of Zoology, University of Michigan, and Mr. 
Walter Koelz, of the same university, a magnificent series was borrowed 
of migrant and winter specimens taken in North Dakota and Arkansas. 
Besides these the important collections of Dr. L. B. Bishop and the Museum 
of Vertebrate Zoology, University of California, have been freely studied. 
Specimens have also been borrowed from, or examined in, the collections 
of the American Museum of Natural History, the Provincial Museum of 
British Columbia, the Philadelphia Academy of Natural Sciences, the 
Museum of Zoology, University of Oklahoma, Dr. Jonathan Dwight, 
Major Allan Brooks, Mr. J. H. Fleming, and Mr. J. A. Munro. The writer 
has also had illuminating correspondence with Mr. H. V. Williams of 
Grafton, North Dakota, Dr. C. H. Richmond, of the United States National 
Museum, and Mr. C. G. Harrold, of Winnipeg, Manitoba. To all the 
above thanks are extended, not only for the courtesies received but in 
particular for their assistance in bringing together for direct comparison 
so fine a series, consisting of 157 skins, with the rarer forms in particular 
abundance, and for detailed notes on half as many more pertinent speci- 
mens. Of special value has been the series of breeding birds and their 
offspring, which has been a key to unlock many difficulties and without 
which no clear picture of the involved relationships could have been obtained. 
41954 — 24 
