54 BULLETIN 196, UNITED STATES NATIONAL MUSEUM 



meadows, with short grass in which the adults might seek their forage, persisted 

 during the summer months. These areas vary from a few hundred square feet of 

 grassland, as along the banks of small creeks, to large level tracts in the high 

 Sierra Nevada, sometimes embracing several square miles of continuous grassland. 

 The number of birds present in any given place usually seems to be proportional 

 to the amount of such forage surface available. 



Such favorable conditions had not previously prevailed in the regions 

 to which the robin has recently extended its breeding range. "But 

 with the development of lawns, with continued moisture supply and 

 'green feed,' various species of insects are able to persist there as 

 larvae during the summer season. With irrigation, earthworms also 

 are able to live up near the surface of the soil when normally they 

 would be aestivating in deep burrows to avoid desiccation." 



A. J. van Rossem (1942) was prompted by recent reports of robins 

 nesting in the vicinity of Pasadena to state that a pair first nested on 

 the grounds adjoining the residence of Donald R. Dickey in 1923; and 

 he remarks significantly: "Generally speaking, it may be said that the 

 transition of Pasadena from a small farming community to a residen- 

 tial city took place in the late 1890's and the early 1900's. It was 

 thus about twenty-five years from the establishment of suitable terri- 

 tory until the robins first made use of it, although the species has al- 

 ways been common in summer in the Transition Zone in the imme- 

 diately ad j acent mountains . ' ' 



Migration. — As many western robins spend the winter as far north 

 as southern British Columbia, the migrations in the northern part of 

 their range are not well marked as north and south migrations. At any 

 time during late fall and early winter, large flocks of robins may be 

 seen moving about from one locality to another in search of suitable 

 feeding grounds, their presence or absence in any one place being de- 

 pendent on the supply of berries or other food. Thus their migrations 

 are mainly local wanderings, coupled with a downward movement 

 from the mountains in the fall and a return to the higher levels when 

 the snows disappear in spring. Mr. Rathbun (MS.) tells me that, in 

 western Washington, "about the close of winter, or sometime during 

 the month of February, single robins or perhaps pairs of the birds will 

 be seen again around the residence districts of the cities and towns." 



In California conditions are somewhat similar, with great variations 

 from year to year in the winter population of robins, depending on 

 the food supply. But there the migration, especially in spring, is well 

 marked. The robins that winter in Mexico and Guatemala have a 

 long way to go to reach their breeding grounds, and large numbers are 

 often seen flying north. 



On February 11, 1929, I saw large flocks migrating over Pasadena 

 flying high and headed northward. On March 6 and 7 large numbers 

 of robins gathered in the camphortrees in front of my house ; the trees 



