Long‐term population dynamics of a migrant bird suggests interaction of climate change and competition with resident species

The separation of abiotic and biotic factors affecting populations and communities is an important step in understanding how climate change can influence ecological processes, but quantifying their relative contribution to community changes is a challenge. We assessed the effect of temperature and species interactions on the population dynamics of a forest bird community with a hierarchical dynamic population model in a Bayesian framework. We used a long-term time-series (1956-2012) of four secondary cavity-nesting birds with similar food and nesting requirements but different migration habits, to analyse the effects of the four species population size and the local weather fluctuations on each species' population dynamics. We found clear evidence of a negative effect of two resident species (blue tit and great tit) on a long-distance migrant (pied flycatcher). Among the residents we only found a competition effect of the great tit on the marsh tit. The birds showed opposite responses to weather: the pied flycatcher favoured colder springs whereas the blue tit and great tit favoured warmer springs. Although alternative mechanisms cannot be ruled out, our results suggest that the resident species (blue tit and great tit) could adjust to increasing spring temperature while the migrant species (pied flycatcher) could not, leading progressively to the exclusion of the pied flycatcher from the area. These results point out the potential role of competitive interactions by providing insightful clues, call for refined research, and support recent efforts to include population dynamics in species distribution models.