Stopover biology: How does ghrelin mediate migratory decision?

Billions of migratory birds move across continents every year, performing long, non-stop flights over ecological barriers such as seas and deserts. During the journey, birds spend about 80% of their time at stopover sites, areas where birds can recover from the fatigue of long flights and refill their energy reserves. Atmospheric factors such as wind and rain influence migratory movements, but eventually the decision of staying longer at the stopover site or departing depends on the conditions of the birds. A recent study of our group showed that a recently discovered hormone, ghrelin, is involved in the regulation of stopover behaviour. Ghrelin is produced in the gastrointestinal tract, and in domestic birds appears to be important to regulate appetite and foraging. We hypothesized that ghrelin variations in the blood circulation tell the birds when it is time to go. We designed a series of experiments to test this hypothesis in wild garden warblers (Sylvia borin) during their passage at a stopover site in the Mediterranean Sea. We will study how ghrelin changes across phases of migration by simulating a long migratory flight and a refueling stopover. We will test the effects of drugs that mimic or counteract the action of ghrelin on migratory behaviour and food intake. In addition, we will investigate variation of the genes that control the production of ghrelin to understand why the relationships between condition, migratory behaviour, and food intake vary between individuals of the same species.

Funding

FWF Stand-Alone Grant P31037-B29

Participants

PI: Leonida Fusani
Silvia Fuselli, University of Ferrara, Italy
Wolfgang Goymann, Max Planck Institute for Ornithology, Seewiesen, Germany
Hiroyuki Kaiya, Natl. Cerebral and Cardiovascular Center Res. Institute, Osaka, Japan
Steve Smith, University of Veterinary Medicine, Vienna