During their migrations, migratory birds are exposed to numerous pathogens. A functioning immune system is therefore crucial when flying into new environments. However, immunity is energetically costly and competes with other important physiological processes. In our latest work, we examined the extent to which fattening before bird migration influences innate immunity using the common quail as our study species.

While many studies showed that the immunity of birds is often weakened during their strenuous migratory flights, it remains little understood if and how immunity changes during the rapid accumulation of energy stores in preparation for migration. To fill this knowledge gap, we induced pre-migratory fattening through controlled changes in daylight and regularly examined changes in three markers of innate immunity – leukocyte coping capacity (LCC), hemagglutination and hemolysis titers. In addition, body composition, namely lean mass and fat mass, was measured.

We found that all three markers showed similar changes during pre-migratory fattening. The LCC responses, hemagglutination and hemolysis titers were on average higher in the middle fattening phase than in the high fattening phase, here the values ​​were similarly high as before the start of pre-migratory fattening. In the middle phase of fattening, we found that the birds that had a higher fat content had lower peak LCC values ​​and hemolysis titers. Conversely, at this time of fattening, the birds with a higher proportion of lean mass had the highest peak LCC values. We proposed that these results could be due to competing or opposing processes between metabolic remodeling and the function of the innate immune system.

These three immune indicators are integral parts of the innate immune system, which acts quickly and effectively against a wide range of pathogens, even without prior exposure. This aspect is crucial in the context of animal migration, as the ability to respond quickly to various threats is crucial for fitness. For the future, we hope that our work will encourage further studies to obtain detailed information about the remodelling of the immune system during the most energetically demanding phases in the life cycle of migratory birds.

Our article “Controlled expression of avian pre-migratory fattening influences indices of innate immunity” by Marcin Tobolka, Zuzanna Zielińska, Leonida Fusani, Nikolaus Huber, Ivan Maggini, Gianni Pola, Valeria Marasco Biol Open 15 January 2024; 13 (1): bio060018. doi: https://doi.org/10.1242/bio.060018 is freely accessible and open access.

We are massively grateful to the PR team at Vetmeduni for helping us to communicate our work to broader audiences: https://www.vetmeduni.ac.at/klivv/ueber-uns/aktuelles