112 UNIVERSITY OF COLORADO STUDIES 



everywhere, pass through twice a year on their northward and south- 

 ward journeys, stopping but a few hours, if at all, to eat and rest. Others 

 come from the south, remain through the summer, and return to their 

 winter homes with the first breath of cold weather. Others spend their 

 summers in the north, rear their young there, but come here for winter. 

 Others remain with us throughout the year. In addition to the usual 

 latitudinal migration, however, we have here a pronounced altitudinal 

 migration. To illustrate, grayheaded juncos breed in large numbers 

 in the mountains, up to timber line. In the winter they come down to 

 the valley to join their cousins from the north, so that one not familiar 

 with their summer range might suppose they also came from the north. 

 Severe weather also brings some of the Rocky Mountain jays down to 

 the valley. The long-crested jay may be seen all summer in the foot- 

 hills, but seldom come into Boulder City until after the first frosts, 

 when they arrive in considerable numbers and remain until spring. 

 There are also reasons for supposing that some species make a sort of 

 altitudinal migration between broods, raising their two broods at different 

 altitudes. Others apparently indulge in erratic movements singly or in 

 flocks after the breeding season and before the southward movement. 

 The erratic movements of such birds as the evening grosbeak are such 

 that it is difficult to connect them with any known change of conditions, 

 though it seems likely that the supply of preferred food would furnish 

 the key to the movements. From this it seems clear that the problems 

 confronting the ornithologist require extensive observations which can 

 only be obtained by scattered observers working in unison. Such work 

 the United States Biological Survey is doing for the country at large, 

 by tabulating the migration records of observers all over the land; but 

 for the local and state problems more minute data are required. 



