Simulating energetically optimal wintering destinations
We used the optimal redistribution simulator (ORSIM) to simulate species’ migratory connectivity based on energy optimization (Somveilleet al. 2021). This model was developed to simulate an ideal optimal redistribution of individuals between the breeding and wintering grounds a species. It balances the minimization of energetic costs associated with relocating between seasonal grounds and the minimization of intraspecific competition for access to resources. ORSIM was calibrated using species’ relative abundance in ecoregions over the study region (see details above) and the energetic cost was solely based on migration distance between sites, thus no climate information was used in the model. A detailed description of the model can be obtained in Somveille et al. (2021).
For each population, we kept the empirical breeding destinations (i.e. occupied ecoregions during the breeding season) and ORSIM generates a simulated set of occupied ecoregions during the wintering season. Climate was extracted and seasonal niche overlap was calculated in the same way as for the observed wintering distributions, but the weight assigned to each simulated wintering ecoregion was the relative number of individuals coming from the empirical breeding distribution of the population.