Organismal robustness and resilience to declining temperature predict reproductive outcomes in a wild bird

Coping with challenges often requires maintaining performance during poor conditions (robustness) and reestablishing normal performance following disturbance (resilience). Trade-offs between performance under normal and challenging conditions may generate variation in stress-coping capacity, but there are few empirical data to test this idea from wild populations. We studied robustness and resilience to declining temperatures in tree swallows (Tachycineta bicolor) using a 39-year dataset. Prolonged periods of cold conditions had profound and sustained impacts on adults and nestlings, including negative associations with mass, growth, and survival. We used over 75,000 h of automated behavioral monitoring data to characterize individual differences in the behavioral robustness and resilience of incubation-bout length and provisioning rates to declining temperatures. Using these estimates, we found that the effects of temperature on nestlings were attenuated by higher robustness and resilience of parental behaviors. Higher levels of parental robustness were, in turn, associated with both developmental cold exposure and baseline corticosterone. As expected, trade-offs between mean behavioral levels and behavioral robustness modulated susceptibility to declining temperatures, with higher mean performance improving outcomes but lower robustness increasing vulnerability. Selection on these trade-offs may generate population differences in vulnerability to changing temperature regimes.