606 ANIMAL LIFE IN THE YO SEMITE 



The robin, of all our birds, least needs an introduction. For this reason 

 we have used it as the standard of comparison for most medium sized birds 

 of the region. Summer travelers in the Sierra Nevada recognize the 

 Western Robin at once as characteristic of the mountains, inhabiting the 

 small meadows which floor the openings in the coniferous forests ; people 

 who live in the foothills and valleys of California know the bird as a winter 

 visitor to their orchards, fields, and gardens. Upon the establishment of 

 towns within either its winter or summer range the robin quickly becomes 

 a dooryard bird, regardless of whether the dooryards are those of perma- 

 nent houses or those of the ephemeral tent cities which, as in Yosemite 

 Valley, grow and vanish with the passage of each summer. 



The robin population varies greatly according to place and season. In 

 nesting time the birds are found only in the Transition, Canadian, and 

 Hudsonian zones, in other words, in the boreal parts of the country; and 

 even within this territory their numbers are not uniform, being greatest 

 in the Transition Zone, as exemplified by Yosemite Valley, and smallest 

 about the relatively sparse forests of the Hudsonian Zone, as about 

 Tuolumne Meadows. On the east slope of the Sierras their numbers at 

 best are small. 



With the cessation of nesting activities the ties which hold the robins 

 to their summer haunts are broken and the birds begin to range more 

 widely. Food then seems to be the controlling factor in their distribution 

 and continues to be so until they return to their breeding grounds the 

 following spring. An abundance of easily obtained berries may bring 

 about a local concentration of robins in one of the upper zones, and con- 

 versely a dearth of forage in the mountains may result in an early depart- 

 ure to the foothills, where adequate forage happens to be obtainable. In 

 1915 Western Robins were present in the high mountains until late, being 

 seen at Ten Lakes on October 10 and at Aspen Valley on October 15 ; in 

 Yosemite Valley they were present in numbers up until November 8, when 

 there was a good fall of snow. The next day few robins were to be seen, 

 nor were more than single individuals encountered thereafter, although 

 we remained in the Valley that year until November 22. 



Only a few venturesome robins continue in the mountains above the 

 3000-foot level during the Sierran winter. Two were noted near Clark 

 Bridge in Yosemite Valley on December 10, 1914, and 10 at Gentrys on 

 the Big Oak Flat road on December 30, 1914. On December 28, 1915, 

 about 150 robins were reported at Crane Flat by one of the Park rangers, 

 although no reason was suggested for such a concentration of the birds 

 at that elevation on the date mentioned. In the foothills during the winter 

 months robins are abundant. At Pleasant Valley, 117 were noted in a 

 3-hour census on December 4, 1915. The return to the higher mountains 



