We investigated the effect of spring temperatures, female age, and female body condition on the timing of laying in a migratory woodpecker, the Northern Flicker (Colaptes auratus), and looked at the relationship between laying date and reproductive success. Average annual laying dates in the population, recorded over 12 years, were not related to the North Atlantic Oscillation or the Pacific-North American climate indices but were earlier when average daily temperatures along the migration route of Northern Flickers along the Pacific coast of North America were warmer. However, the strongest negative correlation between laying dates and ambient temperatures occurred after the arrival of most birds on the breeding site, which suggests that the ability of females to accumulate resources for egg laying on the breeding site was an important determinant of laying times. At the population level, egg laying advanced by 1.15 days for every degree warmer on the breeding grounds. At the level of individuals, laying dates advanced as females aged from 1 to 3 years, and females in better body condition also laid earlier. However, there was no interaction between female age and ambient temperature, which suggests that the age classes had equal capacity to respond to environmental change. Reproductive output declined seasonally as a result of declines in clutch size and not as a result of reduced fledging success. This suggests that there is no ecological mismatch linked to prey availability for Northern Flickers and that individuals could benefit by laying earlier if spring temperatures allow.
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Vol. 127 • No. 4