Dynamic-models of mass-dependent predation, risk-sensitive foraging, and premigratory fattening in birds

The effect of mass-dependent predation on risk-sensitive foraging choices of small birds in two ecological contexts was examined using stochastic dynamic models. In the first context, nonmigratory foraging, predation risk dependent on the bird's body mass leads to risk-adverse behavior in situations where risk-neutral behavior would otherwise be expected and generally reduces the amount of foraging and the level of reserves carried by foragers. In the second context, premigratory foraging, mass-dependent predation can lead to risk proneness during the buildup of reserves for migration. Risk proneness is favored if birds can reduce mass and hence reduce predation after migration, thereby giving them an advantage to rapid departure. Other advantages of early departure can also lead to premigratory risk proneness but require more specific ecological assumptions. The literature on risk sensitivity in amount of food reward suggests a connection between migration and risk proneness on negative energy budgets but more tests are needed before any conclusions can be drawn.