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Nocturnal but not diurnal threats shape stopover strategy in a migrating songbird

Bianco, Giuseppe1; Raj Pant, Sara12; Wu, Xiaojia1; Akesson, Susanne1

Published May 19, 2025 on Dryad. https://doi.org/10.5061/dryad.k0p2ngfk6

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Abstract

Songbird migration involves frequent migratory flights interrupted by several days of stopover to refuel. For first-year migratory birds, this entails stopping in unfamiliar locations to exploit local resources and maximize fuelling rates. However, stopovers also pose mortality risks due to predator presence. We investigated whether auditory cues from two avian predators with contrasting hunting strategies—the diurnal Eurasian sparrowhawk (Accipiter nisus), which captures prey in flight, and the nocturnal tawny owl (Strix aluco), which relies on pouncing attacks—trigger different anti-predator responses in the nocturnally migrating European robin (Erithacus rubecula). We found that robins react to the perceived risk of predation by the nocturnal predator but did not alter their strategy in response to diurnal predator cues. Robins reduced foraging activity under perceived predation risk at night and decreased their fuel deposition rates over the stopover period. Lower body condition after stopover can result in a slower migration pace and consequently later arrival to wintering areas, potentially affecting individual fitness. This novel study highlights the flexibility of avian migration programs in adapting to perceived predation risks based on predator activity time and hunting modalities, and how these adaptations differentially shape stopover strategies.