The long seasonal travels of migratory birds are a well-known phenomenon. But what hormonal processes are involved? A recent study by the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine Vienna identifies sharply rising levels of the hormone ghrelin as a key trigger of migratory restlessness. The recently published research could not, however, confirm a connection with the hormone corticosterone as shown in other studies.

Migratory birds have spectacular physiological adaptations to accommodate the long-distance flights between their breeding and wintering grounds. The animals use fat reserves built up prior to migration as their main source of energy. In both captive and free-flying birds, the migratory phenotype – the physical changes that occur prior to and during migration – is signalled by rapid and marked increases in food and energy intake as well as by changes in nocturnal activity and by migratory restlessness. However, there has been little scientific evidence to date on the exact hormonal mechanisms underlying this process.

Hormone ghrelin makes quail fit for long flights

An international research team led by the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine used common quails (Coturnix coturnix) to assess if  the hormone corticosterone and the gut-derived hormone ghrelin play a role in the seasonal expression of migratory behaviour. For their experiment, the researchers exposed quails to controlled changes in day length  to simulate autumn migration, followed by a wintering period. The researchers then compared corticosterone and ghrelin concentrations and assessed whether these two metabolic hormones varied between migratory states.

“In accordance with our predictions, we found that the emergence of the migratory phenotype was associated with higher concentrations of ghrelin. In addition, ghrelin correlated with changes in body mass of birds as they transitioned into their autumnal migratory state and as they entered the wintering state,” explains the study’s first author, Valeria Marasco from the Konrad Lorenz Institute of Ethology at Vetmeduni.

No correlation between corticosterone levels and migratory restlessness

Contrary to their predictions, however, the researchers observed no correlation between circulating levels of ghrelin and corticosterone. The scientists were also unable to detect elevated levels of corticosterone in the migratory phenotype. “There was no significant correlation between baseline corticosterone levels and changes in body mass, levels of food intake or migratory restlessness (the urge of captive birds to migrate at night)” says the study’s senior author Leonida Fusani, head of the Unit of Ornithology at the Konrad Lorenz Institute of Ethology.

The article "Ghrelin, not corticosterone, is associated with transitioning of phenotypic states in a migratory Galliform“ von Valeria Marasco, Hiroyuki Kaiya, Gianni Pola, and Leonida Fusani was publised in „frontiers“.

Scientific article

2023-01-11