Data from: Flexible response to short-term weather in a cold-adapted songbird

To improve survival during winter, temperate species use a variety of
behavioural and physiological adaptations. Among songbirds, the
maintenance of lipid reserves is a widely-used strategy to cope with the
severity of winter; however, little is known regarding how multiple
synchronously acting environmental mechanisms work together to drive these
effects. In a context where temperate winter conditions are becoming more
variable, it is important to widen our understanding regarding the
flexible adaptations that may allow wintering species to adjust to
projected climate change. Using a long-term dataset collected across
multiple wintering populations (7 years; 8 locations), we analyzed the
effects of daily variation in weather (e.g., temperature, snowfall) on the
variation in energy reserves (i.e., fat stores) of wintering snow buntings
(Plectrophenax nivalis). Our results support the prediction that birds
carry more reserves to increase the safety margin against starvation when
conditions are energy-demanding and access to food is unpredictable (i.e.,
colder, snowier conditions). Birds responded to daily changes in weather
by increasing their reserves as conditions deteriorated, with maximal
temperatures and snow depth being the most important predictors of
fattening decisions. We also found that females consistently exhibited
higher fat reserves than males relative to their body size, suggesting
that differential physiological adaptations among sexes or social
dominance may play an additional role in explaining variation in energy
reserves across individuals in this species. Overall, our findings
increase knowledge on phenotypic adjustments used by species wintering in
temperate zones to match variation in their environment.