Birds 57 



59. In 1873 Ridgway added 60, in 1876 H. W. Henshaw 14, 

 in 1877 Ridgway 21. For many years following additional rec- 

 ords came in, one or a few at a time, but as late as 1897 

 W. W. Cooke was able to add 19, bringing the list up to 363 species 

 and subspecies. Sclater, in his great work published in 1912, 

 recorded in all 392 kinds of Colorado birds.* Although this is a 

 very large number, it includes no less than 167 which do not breed 

 within the state. Of these, 106 are classified as casual visitors, 

 not belonging to the Colorado fauna in the strict sense. Twenty- 

 eight are winter residents, and 33 merely pass through the 

 State during the spring and fall migrations. This leaves 225 

 regular breeders, the true Colorado avifauna. Of these only 67 

 are regular and permanent residents throughout the year; the 

 rest usually or regularly go south in winter. This analysis is 

 derived from Sclater, and would not be materially altered by 

 subsequent publications. Sclater makes a further classification 

 of the 225 regular breeders, according to their breeding places. 

 Thirty-five breed on the plains and up to about 6,000 feet; 80 breed 

 on the plains and in the foothills and parks, up to about 8,000 feet; 

 33 breed throughout the plains and up into the mountains to 

 1 1,500 feet and upwards; 14 breed in the foothills and parks, be- 

 tween 6,000 and 8,000 feet; 24 breed in the mountains, from 6,000 

 to 1 1,500 feet; 39 are chiefly confined in the breeding season to 

 the mountains, between 8,000 and 1 1 ,500 feet. 



Birds maintain a high temperature;** this makes it neces- 

 sary to have a large amount of food. Henderson cites the follow- 

 ing examples: "a young robin in captivity ate 50 to 70 cutworms 

 and earthworms daily from May 21 to June 6, and on June 9, 

 when the bird weighed exactly three ounces, it consumed 165 

 cutworms, which weighed altogether 5^ ounces, nearly twice the 

 weight of the bird. Another robin on the fourteenth day of its life 

 ate 68 worms, which weighed 41 % more than the bird. One snowy 

 owl contained 14 white-footed mice and three meadow mice. A 

 golden eagle in captivity will consume two pounds of fresh meat 

 daily. A Cooper's hawk reared by Judd frequently ate its own 

 weight of food in a day, and another, six weeks old, was observed 



*A later estimate increases the number to over 400. 



**Wetmore haa recently published seme very interesting observations on the function of 

 the air-spaces in the bones, in relation to the body temperature. Birds differ from mammals 

 in having no sweat glands. 



