Temperature change is an important departure cue in nocturnal migrants: controlled experiments with wild-caught birds in a proof-of-concept study.

The decision-making process of migrating birds at stopover sites is a complex interplay of the innate migration program and both intrinsic and extrinsic factors. While it is well studied how variation in precipitation, wind and air pressure influence this process, there is less evidence of the effects of temperature changes on the departure decision. Thus, we lack knowledge on how the predicted changes due to global climate change in temperature alone may affect the decision-making process during migration. Aiming to fill parts of this gap, we conducted a proof-of-concept study by manipulating the ambient temperature of temporarily confined wild-caught migrant songbirds under constant feeding conditions. In spring, departure probability increased with a 20°C rise in temperature for both a medium-distance migrant (European robin, Erithacus rubecula) and a long-distance migrant (northern wheatear, Oenanthe oenanthe), and in autumn, departure probabilities of the long-distance migrant both decreased with a 20°C rise and increased with a 20°C drop. Consequently, the temperature is an important departure cue influencing the decision-making process of migrating songbirds. Incorporating causal relationships between changes in temperature and departure probability in migration models could substantially improve our ability to predict the effects of climate change on the phenology of migratory birds.