A framework for reproductive outcomes of phenological match-mismatch in migratory breeders tested on a declining species, caribou

Long distance migrants with endogenously timed reproduction may be especially vulnerable to phenological mismatch on summer ranges where offspring are produced and provisioned. This is because departure timing from winter ranges and breeding timing on summer ranges in such species is cued primarily by photoperiod while the timing of resource availability on summer ranges is cued by local temperature. Hence, studies of climate change driven mismatch have focused nearly exclusively on one aspect of resource phenology: the timing of resource availability on summer ranges. Here we present a predictive framework for reproductive outcomes in long-distance migrants that integrates the seasonal timing and rate of increase in resource availability on summer ranges. The framework predicts that potential disadvantages of early resource availability relative to resource demand may be buffered by slow rates of increase in seasonal resource availability. Conversely, potential advantages of later resource availability that coincides with the timing of resource demand may be unrealized if resource availability increases too rapidly. We test the framework using 21 years of offspring production by tundra caribou, a long-distance migratory breeder whose global abundance is in decline, whose timing of reproduction is endogenously entrained, and for whom resource availability on summer ranges may advance with local warming. Agreement with empirical outcomes for caribou in this case study suggests broader utility of this framework for predicting climate change consequences for phenological match-mismatch in other long distance migratory breeders.