Effect of fuel load, date, rain and wind on departure decisions of a migratory passerine

Meteorological conditions, fuel load and date in the season can affect the departure decisions among migratory birds. However, it is poorly understood to what extent the departure decisions are more influenced by some parameters in relation to others, and how they interact with each other. We explored here how fuel load, date, rain and wind (measured on the ground and at high altitude, codified as a tailwind component) influenced the departure decisions of migratory Blackcaps (Sylvia atricapilla) from a stopover site. We used mark recapture data of 947 Blackcaps collected during the autumn migration period 2005 at a stopover site in northern Iberia, estimating the emigration likelihood with Cormack-Jolly-Seber models, in which we tested for the effect of these four study variables. Best models fitting data showed an additive and positive effect of tailwind and fuel load on the emigration likelihood.