Seasonal effects of climate and land use changes on ecological niche of a migratory bird

Abstract Background: The habitat selection strategies followed by migratory populations are a major concern for conservation and management. Consequently, the ability to predict their distribution and potential changes in migratory behaviour is a pressing challenge for ecological modelling in a changing world. There are two main strategies of habitat selection adopted by migratory animals: tracking optimal conditions or acclimatizing to a changing environment between seasons. In this study, we investigate the variations in ecological niche of gps-tracked American White Pelicans (AWPE) associated with their seasonal migration. We also investigated whether recent changes in food resources in their wintering grounds have exerted an impact on the habitat selection behaviour of AWPE. Methods: We developed Maximum Entropy (MAXENT) Species Distribution Models (SDM) using data from GPS-tracked AWPE. We then compared climatic and land-cover niche breadth and overlap between their breeding and wintering grounds in relation to the facultative migratory behaviour of AWPE. Results: Our climatic, land-cover, and combined SDMs obtained a high predictive performance. Several lines of our findings support our hypothesis that AWPE habitat selection strategy follows the “niche switcher” theory. American White Pelicans showed little climatic niche overlap between nesting and wintering seasons. Migrants in the breeding grounds showed broader climatic niche than residents and migrants in the wintering grounds. Finally, declines in availability of food resources provided by commercial aquaculture in their wintering grounds appeared to affect the niche variations of AWPE, with land-cover niche being narrower before than after the decline in aquaculture. Conclusions: If AWPE can effectively adapt and occupy different niches when they migrate instead of tracking suitable climate conditions, this can have important implications in the context of Global Change, since they might respond unexpectedly to anthropogenic changes, like the recent decline in aquaculture as a food resource reported here.