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Garden warbler. Credit: Wolfgang Goymann

Every year, billions of birds make the long journey from subSaharan Africa to Europe and back. The majority of migratory species that undertake this gruelling journey need to make ‘pitstops’ on the way, in order to replenish their fuel reserves. But what signals tell the birds when they have eaten enough to allow them to move on again?

Goymann et al. studied wild garden warblers (Sylvia borin) at a well known stop-over site for the species on the island of Ponza in Italy. They found that birds with high fat scores (i.e. those that were well nourished) had higher acylated ghrelin concentrations compared with those with lower fat scores. Additionally, when the birds were given an injection of unacylated ghrelin, their food intake decreased, while their migratory restlessness increased.

This study provides the first evidence for a role for the appetite-regulating hormone ghrelin in the control of migratory behaviour, linking how ecologically dependent factors such as condition can affect the timing of migration.

Read the full article in Proceedings of the National Academy of Sciences of the USA doi:10.1073/pnas.1619565114