Convective rainfall drives behavioral shifts across multiple foraging scales in breeding seabirds.

Abstract

BACKGROUND: Rainfall can influence seabird foraging behavior through interactions with other climatic variables, such as wind speed and cloud cover, causing both immediate constraints on flight and foraging activity and longer-term changes via shifts in prey distribution. To understand the ecological significance of rainfall, it is therefore necessary to examine foraging behavior across multiple spatiotemporal scales. Rainfall can be broadly classified into convective and large-scale types based on spatial extent and persistence, yet their distinct effects on seabird foraging behavior have rarely been explicitly tested. METHODS: We examined how two types of rainfall (convective and large-scale rainfall), cloud cover, and wind speed relate to foraging behavior and chick growth in streaked shearwaters (Calonectris leucomelas) rearing chicks on Awashima Island, Japan, from 2011 to 2024. Foraging behavior was quantified at three spatiotemporal scales: (1) fine-scale behavioral states (traveling, foraging, and resting), estimated using a hidden Markov model; (2) meso-scale trip parameters, including maximum range and trip duration; and (3) broad-scale behavioral specialization, quantified as Individual Foraging Site Fidelity (IFSF). Chick growth rate was used as a proxy for the cumulative outcomes of foraging behavior. RESULTS: Increased convective rainfall was associated with higher transition probabilities from other states to the foraging state and with higher IFSF. In contrast, increased large-scale rainfall was associated with lower transition probabilities from the foraging state to other states, longer maximum range, and lower IFSF. In addition, wind speed was associated with changes in fine-scale behavioral states and meso-scale trip parameters, whereas cloud cover showed no ecologically meaningful effects. None of the climatic factors examined were associated with chick growth. CONCLUSIONS: Short-term, localized convective rainfall is likely to alter foraging conditions in ways consistent with its defining characteristics, leading to rapid switches to foraging behavior and higher IFSF through increased patchiness in prey distribution. In contrast, because large-scale rainfall is persistent and spatially extensive, it likely promoted sustained foraging behavior and more homogeneous prey distributions, resulting in lower IFSF. By examining climatic effects across multiple spatiotemporal scales, this study contributes to a more comprehensive understanding of how climate change influences seabird foraging behavior.