480 U.S. NATIONAL MUSEUM BULLETIN 237 part i 



and fed the female, who appeared to arch her back and flutter her 

 wings as he fed her. After he left she kept up a constant high-pitched, 

 excited chatter, accompanied by a fluttering of the wings. 



Eggs. — The usual set of four eggs is pale bluish green and unmarked. 

 Hanna (1924b) weighed 27 eggs of the green-backed goldfinch; these 

 ranged from 0.87 to 1.15 grams and averaged 1.05 grams. 



The measurements of 50 eggs average 14.7 by 11.2 millimeters; 

 the eggs showing the four extremes measure 16.3 by 12.2, and 12.7 by 

 9.7 millimeters. 



Young. — W. Lee Chambers (1915) traced the history of a green- 

 backed goldfinch's nest in southern California in April 1915. The 

 nest was started on April 4 in a lemon tree in which the pair had been 

 present for several days and was lined with feathers and nearly com- 

 pleted by April 11. On the 17th at 6:00 a.m. the nest contained a 

 full set of four eggs and by 6:30 a.m. on April 29 all four eggs had 

 hatched. The incubation period, then, is 12 days, which is what 

 Gross (1938) reported as the incubation period for the American 

 goldfinch. 



Law (1929) made the following observations on nesting green- 

 backed and Lawrence's goldfinches at Altadena, Calif.: "In both, 

 with the approach of the breeding season and during incubation, the 

 male feeds the female by regurgitation. The parents of both species 

 feed their young by regurgitation. The young of both species appear 

 to be raised entirely on seed food, mostly seeds 'in the milk.' The 

 nests of each species is * * * kept clean by the parents during the 

 first days after the young emerge from the eggs. By the time the 

 young are half grown, such effort is abandoned, and the rims of the 

 nests become filthy with fecal matter. The feces of the young of both 

 at this stage are without membranous sacs and are, for this reason, 

 less readily eaten or carried off." 



Food. — Goldfinches forage in flocks most of the year. They move 

 through the bushes and trees that provide the major part of their 

 food, and they sometimes concentrate on low-growing herbaceous 

 plants. Most of their food is plant material, including buds, leaves, 

 fruits, and seeds. Some animal food is eaten, but the kind and amount 

 are difficult to identify by observation of the living birds. On the 

 Hastings Reservation 55 kinds of plant food have been identified as 

 eaten by the green-backed goldfinch. Prominent among these are 

 chamise, common fiddleneck, vinegarweed, and Napa thistle. 



According to Beal (1910) weed seed is the standard food of this 

 goldfinch, representing over 96 percent of the year's diet. In January 

 and March nothing else was eaten. Animal food was found in 50 

 stomachs collected in June, July, August, and September, more than 

 half of them in August. The great bulk of it was plant lice; one 



