Stopovers for sickly songbirds

The understanding of the interplay of movement, behaviour and physiology that biologging offers has applied relevance for a range of fields, including evolutionary ecology, wildlife conservation and behavioural ecology. In recognition of this, the Journal of Animal Ecology has an upcoming Special Feature on Biologging  (submissions due 20th September).

This blog posts is written to accompany a recent publication in the Journal of Animal Ecology. Lead-author Dr Arne Hegemann is a Researcher at the Department of Biology at Lund University in Sweden. An eco-physiologist studying the interplay between physiology and ecology, Arne is interested in how immune function influences life-history decisions in general and migration in particular. 

If we humans get sick, e.g. catch a cold or have the flu, we don’t like, or can’t, go for a run or do any other sports. But what do birds do when they get sick during migration?


To answer this question, we caught small songbirds during their autumn migration in southern Sweden. We took a blood sample and attached a tiny (0.3 g) radio-transmitter to each bird. In half of all birds, we stimulated the immune system with a mimicked bacterial infection. Afterwards we released all birds, and an automated radio-telemetry system was constantly registering the presence of each bird.

We showed that those birds that received a mimicked infection stayed longer before they continued with their migration than the un-challenged birds. Hence, if birds are sick during migration, they take a rest and don’t do a migratory flight, just as we humans don’t go for a run when we are sick. Interestingly though, individuals of those species that fly all the way to Africa to winter south of the Sahara, just stayed one extra day, while individuals of those species that only migrate to Western Europe stayed for two extra days.

This suggests that birds, which need to fly to Africa are under bigger pressure to continue migration and to ensure an early arrival in Africa. Reasons may include that their main food (insects) decreases rapidly in autumn. The telemetry data furthermore showed that the birds don’t simply sit still when being “sick”, but they don’t fly around as much as the other birds. Finally, the condition of their immune system before the simulated infection had an influence on how long they stayed. As better the immune system as smaller the effect.

Taken together, our study shows that the immune system and the effect of a possible infection can have important consequences for the migration of small birds. This knowledge will help us understand the timing and behaviour of migration, especially under the threats of climate change when pathogens may spread.

More info:

Hegemann, A., Alcalde Abril, P., Sjöberg, S., Muheim, R., Alerstam, T., Nilsson, J. Å., and Hasselquist, D. (2018). A mimicked bacterial infection prolongs stopover duration in songbirds–but more pronounced in short‐than long‐distance migrants. Journal of Animal Ecology.


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