The American Goldfinch, Spinus tristis tristis, begins breeding later than any other bird in the north temperate zone. The breeding season in Iowa extends approximately from early July to late September. Data from observations on 30 nestings (124 eggs) indicate that if the breeding season is divided in half, the percent of eggs hatching is seen to decrease from 87% to 57%, and the percent of young fledging from 95% to 62% in the latter half. There is considerable evidence that breeding is cued by the blooming of thistle (Circium spp.), a plant upon which goldfinches depend for nest-lining and food for the young. Apparently exploitation of this abundant resource provides an advantage sufficient to outweigh the problems of a relative decrease in nesting success due probably to increased predation pressure later in the breeding season.
Proceedings of the Iowa Academy of Science
©1970 Iowa Academy of Science, Inc.
Lynch, Carol B.
"The Reproductive Strategy of the American Goldfinch, Spinus tristis tristis, in Iowa,"
Proceedings of the Iowa Academy of Science, 77(1), 164-168.
Available at: https://scholarworks.uni.edu/pias/vol77/iss1/24