Northern Wheatear (Oenanthe oenanthe) Science Article 3
Selection for early arrival is expected to shape optimal stopover decisions in migrating birds to minimise time spent on migration. Optimality models predict that fuel loads at departure from stopover sites and stopover duration should depend strongly on search and settling costs as well as on individual fuel deposition rates. In previous years little attention was paid to natural search and settling costs. In the Northern Wheatear Oenanthe oenanthe, a nocturnal long distance migrant, we found evidence for low search and settling costs suggesting that these birds have the capacity to gain body mass from the first day of stopover. Positive correlation between fuel deposition rates and departure fuel loads in males met model predictions for time minimising strategies with an expected global variation in fuel deposition rates and search and settling costs of less than one day. Assuming such low search and settling costs, a time minimising migrant experiencing a stopover site with average fuel deposition rates of 4% of lean body mass is expected to depart with fuel loads less than 17% of its lean body mass. Data on fuel loads from different stopover sites in Europe show that Northern Wheatears generally fulfil these model predictions. Such low fuel loads are expected to force the birds to rest and refuel daily.
Delingat J., Dierschke V., Schmaljohann H., Mendel B. & Bairlein F., ARDEA 94 (3): 593-605.