BOBIN 



607 



is accomplished by the birds as early as food conditions permit, irrespective 

 of weather. Only 5 were seen at Pleasant Valley in a 3i/2-li0^r census on 

 February 27, 1916; yet the population had not moved much higher into 

 the mountains since none was noted in Yosemite Valley the following day. 

 By the end of April (1916), however, robins had appeared in usual num- 

 bers in Yosemite Valley. East of the mountains, the robin population is 

 doubtless altogether absent during the winter months. 



In late spring and throughout the 

 summer the robins go about in pairs 

 when one or the other bird is not in 

 attendance at the nest. After the 

 3''0ung are grown, family parties are 

 to be seen for a while. As soon as 

 the young are capable of getting their 

 living independently they gather into 

 flocks. Meanwhile the adults go off 

 by themselves and remain sequestered 

 until completion of their annual molt. 

 Then, in late September, the robins, 

 without regard to sex or age, gather 

 into mixed flocks and, for the most 

 part, spend the winter in such gather- 

 ings. These flocks include anywhere 

 from 4 or 6 up to half a hundred 

 individuals. We observed flocks of 10 to 20 in many places in the 

 mountains during September and October, 1915. The flock formation is 

 always loose, and individuals leave and rejoin it at will. For a species 

 like the Western Robin, which subsists largely on crops which fluctuate 

 greatly from year to year as well as from place to place, the flocking habit 

 must be of decided advantage as an aid in locating an adequate supply of 

 food. 



The two sexes are very much alike in the robin. Male birds are slightly 

 the larger, their breasts are on the average darker colored, and their bills 

 in summer are nearly clear yellow. Some females are as dark colored on 

 the breast as the lighter males, but their bills are always more or less tinged 

 with dusky. Specimens of robins collected in the late summer show that 

 the plumage of the female is more worn than is that of the male. This 

 may be taken to indicate that to the female falls the greater proportion 

 of the engrossing duties of incubation and caring for the brood. The 

 young, in juvenile plumage, have many rounded black spots which are 

 sharply defined against the whitish or buffy under surface of the body, 

 and the feathers of the back have whitish shaft streaks and black tips. 



Fig. 60. Western Robin in Juve- 

 nal plumage. Photographed on a porch 

 in Yosemite village, July 31, 1915. 



