PERIODIC FOOD AVAILABILITY AND STRATEGIC REGULATION OF BODY-MASS IN THE EUROPEAN STARLING, STURNUS-VULGARIS

1. The hypothesis that European Starlings, Sturnus vulgaris, regulate their body mass in response to availability of food was tested in two experiments. The first experiment investigated the response to periodi c food deprivations of 6 h, beginning at a random time in the day. The second experiment examined the response to fixed and variable food de privations, and whether this response differed according to 'season', which was manipulated photoperiodically. 2. In the first experiment, t he food deprived birds responded by increasing body mass, in accordanc e with the adaptive regulation hypothesis. 3. The second experiment de monstrated that the response to food availability differed according t o photoperiodic history; birds that were photosensitive responded to a decrease in time available to feed by increasing body mass, whereas b irds that were photorefractory did not. 4. Contrary to theoretical pre dictions, there was no indication that the response to variable time o f onset deprivations was larger than the response to deprivations that began at a fixed time of day. 5. It is suggested that different strat egies of mass regulation at different points in the annual cycle may b e a response to season-specific costs and benefits of fat storage, or may relate to season-specific changes in environmental stochasticity.