美洲金翅雀

Spinus tristis (Linnaeus)

Lemon (1969) reported a goldfinch parasitized by a brown-headed cowbird near Victoria, southern Vancouver Island. This record must refer to the host subspecies S. tristis jewetti, which is an addition to the host catalog. Of the subspecies 5. tristis salicamans, no fewer than 13 parasitized sets of eggs, all from California (Merced, San Benito, Ventura, Los Angeles, and San Diego counties) are in the collections of the Western Foundation. These 13 constitute 6.8 percent of 191 sets of that subspecies in that collection; the host frequency is about the same for the Foundation's material of eastern S. tristis tristis—3 parasitized sets (6.6 percent) of 45 sets there. However, in 4 “source studies” of the eastern goldfinch population from Quebec and Michigan (Friedmann, 1963:147–148) there were only 19 parasitized nests out of 1484 reported, an incidence of only about 1.3 percent. Of 49 nests from Saskatchewan, Manitoba, and Alberta reported to the Prairie Nest Cards files at Winnipeg, only 2 (4.0 percent) were parasitized; of 439 nests in Ontario, 18 (4.1 percent) were parasitized (Ontario Nest Records, Toronto); the files at Cornell University show 12 (3.1 percent) of 390 nests were so affected.

During 1968 and 1969, one of us (S.I.R.) found 12 nests of this species in Cheboygan and Emmet counties, Michigan. One of these nests was parasitized. The cowbird egg hatched 2 to 4 days before the 5 goldfinch eggs began to hatch. However, the cowbird showed little weight gain. On 22 July 1968, the day it probably hatched, the cowbird weighed 2.8 g. On 23 July, it was 3.5 g, and on 24 July it was dead and weighed 2.5 g. Evidently, the cowbird was not adequately nourished by the diet of regurgitated seeds this cardueline finch normally feeds to its young. Interestingly, on 24 July, the dead cowbird was draped over the nest rim in a manner similar to that in which cardueline finches drape fecal sacs around the sides of their nest.

LESSER GOLDFINCH