Modularity in temporal co-occurrence networks at a stopover site reveals strong co-migration fidelity in African-European migratory landbirds over time

Abstract

Migratory species are changing the timing of departures from wintering areas and arrival to breeding sites (i.e., migration phenology), as response to climate change to exploit maximum food availability at higher latitudes and improve their fitness. Despite the impact of changing migration phenology on migratory connectivity at population and community level, the extent to which such individual and species-specific response affects associations among co-migrating species has been seldom explored. By applying temporal co-occurrence network models on 15 years of standardized bird ringing data at a spring stopover site, we show that African-European migratory landbirds tend to migrate in well-defined groups of species with high temporal overlap. Such co-migration fidelity is significantly increasing over the years and higher in trans-Saharan than North-African migrants. Our findings suggest non-random patterns of associations in co-migrating species, possibly related to the existence of regulatory mechanisms associated with changing climate conditions and different uses of stopover sites by migrants, ultimately influencing the global migration economy of landbirds in the Palearctic-African migration system.