Manon Ghislain, Timothée Bonnet, Ugoline Godeau, Olivier Dehorter, Olivier Gimenez, Pierre-Yves Henry

Synchronous variation in demographic parameters across species destabilizes populations, metapopulations and metacommunities and increases extinction risks. Revealing the processes that synchronize population dynamics across species allows to identify trans-specific demographic processes that are subject to environmental forcing of overarching importance. Using a Bayesian, hierarchical multi-site, multi-species mark–recapture model, we investigated synchrony in annual adult local survival across 16 species of songbirds over France for the period 2001–2016, and the contributions of winter and spring weather conditions to synchrony. Adult annual survival was largely synchronous among species (73% [47–94] of Species-by-Year variance), despite species differing in ecological niche and life-histories. This result was robust to differences in migratory strategy among species, uneven species sample sizes, and time de-trending. Shared synchrony across migratory strategy suggests that environmental forcing during the 4-month temperate breeding season has large-scale, cross-specific impacts among songbirds. At a scale ~1000 km a likely proximate mechanism of synchronization is forcing by weather-driven variation in resources, which, in particular, determines the cost of reproduction. However, the strong synchrony was not easily explained by climate, with spring weather variables explaining only about 1.4% [0.01–5.5] of synchrony, while the contribution of large-scale winter weather indices may be stronger, but uncertain (12% [0.3–37]). Future research should up-scale these results to community dynamics, to understand compensatory intra- and inter-specific demographic processes that preserve meta-communities from synchronization.