Breeding Dispersal of Baltic Dunlins Is Not an Adaptive Response to Unpredictable Nest Flooding

Abstract

ABSTRACT Human‐driven habitat loss and climate change are rapidly degrading bird breeding habitats worldwide. For ground‐nesting shorebirds using low‐lying shore habitats, nest failure is primarily driven by predation but can also result from intensified temporary flooding. In the Bothnian Bay, flood‐related nest losses of the Baltic dunlin ( Calidris alpina schinzii ) have drastically increased over the past two decades (from 10% to 46%), compounding the primary threat of nest failure. Breeding dispersal, the decision to relocate from a previous nest site, may offer a behavioral response to such threats. Using long‐term reproductive data from 184 individuals over 20 years and multivariate generalized linear mixed models, we examined local (within‐site) between‐year dispersal distances in relation to nest fate, its influence on subsequent reproductive success, and whether dunlins react to unexpected flooding by dispersing away from the shoreline. We found that between‐year dispersal tended to be higher following nest failure, particularly in males. However, dispersal distances had negligible effects on daily nest survival in the following year. Finally, dunlin males that experienced flooding did not show consistent nest relocation away from the shoreline. Our results suggest that Baltic dunlins relocate regularly within their breeding site, but dispersal is influenced by individual variation and nest fate rather than acting as an adaptive response to environmental threats. These findings suggest that threatened bird populations breeding solely on coastal meadows may be unable to cope with environmental change such as unexpected flooding and are therefore more likely to face extinction without further conservation management.