BLACK ROSY FINCH 369 



of the folded wing where the overlapping primaries, secondaries, and 

 their coverts make an almost solid area of pink. However, the in- 

 tensity of this color may vary considerably in any single population. 

 The female is generally duller than the male, with less extensive pink 

 and a gray crown patch that may be barely detectable. 



The postnuptial molt takes place during approximately the same 

 time of year as the postjuvenal molt and is complete. During this 

 time also the solid black pigmentation of the bill begins to fade until 

 the winter condition is attained, when the bill is yellow except for 

 the very tip, which remains black. It starts to darken again during 

 March just prior to spring migration. 



Food. — The rosy finches subsist primarly on a diet of seeds but 

 supplement this with insects when they are available. During the 

 first few days of nest life the young are given only insects the female 

 collects in the vicinity of the nest. When the young birds begin 

 receiving more seeds, both parents are kept busy maldng long trips 

 to the tundra where they show a preference for foraging along the 

 edges of melting snowbanks. In winter large flocks settle on any 

 spot of bare ground to search for seeds, or they thoroughly examine 

 plants, such as Russian thistle, protruding from the snow. 



During the breeding season rosy finches of both sexes develop a 

 pair of gular sacs capable of considerable distension and opening from 

 the floor of the mouth. This accessory food-carrying structure is 

 definitely advantageous to a species whose nest may be some distance 

 from the feeding grounds. Besides the North American species of 

 rosy finches, gular sacs are known only from one other fringillid, the 

 pine grosbeak, Pinicola enucleator (see French, 1954). 



Analysis of the contents of crops and gular sacs of 70 summer speci- 

 mens of black rosy finch has shown that the food of these birds con- 

 sisted of 97.2 percent seeds and 2.8 percent animals, including mites, 

 nematodes, and various insects. The seeds were those of the small 

 tundra plants abundant in the habitat where the birds are found, the 

 foUowing genera being the most abundant : Siversia, Arabis, Smelowskia, 

 Silene, Lewisia, Sibbaldia, Claytonia. 



Behavior. — Rosy finches are very social bu'ds. It is unusual to see 

 an individual alone. During most of the year they may be found in 

 large flocks, feeding together and flying off together. Only at the 

 approach of breeding do negative social forces develop strongly 

 enough to cause antagonism and breaking up of the groups. The 

 groups re-form in late summer, even while the young are still being 

 fed by the parents, as the positive social forces recrudesce. 



The flocks are closely knit and, when one bird chirps and flies, the 

 entire group literally explodes in an effort to follow. With two 

 young birds raised in captivity, the one irresistible stimulus was 



