DOMINANT AND SUBORDINATE FATTENING STRATEGIES - A DYNAMIC GAME

We model overwinter fattening strategies of dominants and subordinates as a stochastic dynamic game, basing our model on data pertaining to willow tits in Sweden. In the model the birds have two foraging habita ts, one (outer branches) relatively rich in resources but also high in predation risk, the other (inner branches) less productive and less r isky. The dominant is able to exclude the subordinate from the habitat it is currently using. Fluctuations in weather result in variable dai ly metabolic costs. The model predicts that in certain circumstances s ubordinates maintain a higher level of fat reserves than dominants, th ereby hedging against uncertain future metabolic costs and restricted foraging opportunities. Acquiring larger fat reserves exposes the subo rdinate to higher levels of predation risk, reducing its probability o f surviving the winter, relative to the dominant. The model's predicti ons are in agreement with observations and experiments, and lend suppo rt to the hypothesis that winter fattening strategies are complex adap tations to specific environmental, spatial, and social conditions.