Abstract
Many avian migrants have not adjusted breeding phenology to climate warming resulting in negative consequences for their offspring. We studied seasonal changes in reproductive success of the greater snow goose (Anser caerulescens atlantica), a long-distance migrant. As the climate warms and plant phenology advances, the mismatch between the timing of gosling hatch and peak nutritive quality of plants will increase. We predicted that optimal laying date yielding highest reproductive success occurred earlier over time and that the seasonal decline in reproductive success increased. Over 25 years, reproductive success of early breeders increased by 42%, producing a steeper seasonal decline in reproductive success. The difference between the laying date producing highest reproductive success and the median laying date of the population increased, which suggests an increase in the selection pressure for that trait. Observed clutch size was lower than clutch size yielding the highest reproductive success for most laying dates. However, at the individual level, clutch size could still be optimal if the additional time required to acquire nutrients to lay extra eggs is compensated by a reduction in reproductive success due to a delayed laying date. Nonetheless, breeding phenology may not respond sufficiently to meet future environmental changes induced by warming temperatures.
Highlights
Many avian migrants have not adjusted breeding phenology to climate warming resulting in negative consequences for their offspring
After 25 years, maximum reproductive success of early-nesting birds increased over time to reach 0.74 young, a 42% increase
Long-distance arctic migrants like geese are under a strong pressure to lay early in the season to maximise their reproductive success
Summary
Many avian migrants have not adjusted breeding phenology to climate warming resulting in negative consequences for their offspring. Processes occurring at low trophic levels, such as onset of vegetation growth or insect outburst, typically advance at a faster rate in response to warming than those occurring at higher trophic level, such as the phenology of breeding birds[15] This may result in mismatches between offspring hatch and peak food availability with negative consequences for offspring survival[14,16]. The consequences of trophic mismatch are exacerbated in Arctic-nesting geese because their breeding cycle is relatively long, they breed in highly seasonal environments where the summer is short and they are exposed to rapid climate w arming[21] In this environment, the time window to achieve optimal reproductive success is narrow, leaving few opportunities for individuals to adjust laying date to changing environmental c onditions[22]. Females may trade off a reduction in clutch size for an advance in hatching date to reduce the fitness cost associated with a delayed laying[7]
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