Temperature-correlated shifts in the timing of egg-laying in House Finches Haemorhous mexicanus

Abstract

Although temperature-correlated shifts in the timing of egg-laying have been documented in numerous bird species, the vast majority of species examined to date have been those that breed in Europe and have an animal-based diet during breeding. However, given that the timing of breeding can be driven, either in the proximate or in the ultimate sense, by seasonal fluctuations in food availability, the relationship between temperature and laying may differ with diet. Here, we report on patterns of reproductive timing in House Finches Haemorhous mexicanus, a North American species that breeds on a primarily seed-based diet. Analysing nest records from House Finches in California spanning more than a century, we found that egg-laying occurred significantly earlier in warmer springs. We also found that although the timing of egg-laying does not show long-term changes in most of California, in the hottest region of the state (the southeast desert basin) it has advanced significantly.