How and why avian reproductive success varies in response to precipitation: A global meta-analysis.

Precipitation influences animal physiology, behavior, and ecological interactions, therefore affecting demography. However, the nature and strength of those effects vary widely, have been attributed to mechanisms operating over different time scales, and may depend on species-level attributes. We conducted a global meta-analysis accounting for shared evolutionary history to a) understand the nature of relationships between precipitation and avian reproductive success and b) test alternative hypotheses explaining where and why precipitation affects some bird species more than others based on species-level attributes or environment. The nature and magnitude of responses to precipitation were unrelated to species attributes but were dependent upon the timing of precipitation and geographic context. Birds responded negatively to precipitation that fell during the nesting period, while birds responded positively to precipitation that fell prior to the breeding season. Responses to precipitation varied with elevation and latitude; at high elevations at high latitudes, birds experienced lower reproductive success following precipitation, while at high elevations at low latitudes (i.e., in the tropics), the responses were opposite, though sample sizes at high elevations in the tropics were small. Negative responses in colder regions likely reflect direct thermogenic consequences of wetting. In warmer regions, because positive responses to precipitation were unrelated to diet or predation risk, responses to precipitation were likely indirect and mediated by vegetation. Ultimately, this study implicates both direct and indirect responses to precipitation that depend on the timing of precipitation and biogeographic context with large implications for avian populations under changing climate regimes.