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 periodic food deprivations of 6 h, beginning at a random time in the day. The second experiment examined the response to fixed and variable food deprivations, and whether this response differed according to 'season', which was manipulated photoperiodically. 2. In the first experiment, the food deprived birds responded by increasing body mass, in accordance with the adaptive regulation hypothesis. 3. The second experiment demonstrated that the response to food availability differed according to photoperiodic history ; birds that were photosensitive responded to a decrease in time available to feed by increasing body mass, whereas birds that were photorefractory did not. 4. Contrary to theoretical predictions, there was no indication that the response to variable time of onset deprivations was larger than the response to deprivations that began at a fixed time of day. 5. It is suggested that different strategies of mass regulation at different points in the annual cycle may be a response to season-specific costs and benefits of fat storage, or may relate to season-specific changes in environmental stochasticity.