Energetic state during learning affects foraging choices in starlings

We investigated the influence of energetic state at the timeof acquaintance with a new food source on preference for thatsource on later encounters, using wild-caught European starlingsas subjects. Twelve birds learned to obtain food rewards bypecking at either of two keys identified by color. The keyswere encountered in different sessions, while the subjects werefood deprived or prefed. Food rewards from both sources werealways identical. After an equal number of reinforced trialswith each source, the birds were presented with choices betweenthem. The birds significantly preferred the source that hadpreviously delivered food under higher deprivation. We relatethese results to findings reported elsewhere of preferencesfor options previously associated with greater effort. We hypothesizethat subjects may attribute value to an option according tothe marginal fitness gain associated with this option in thepast. Although this process may be adaptive under many circumstances,it violates the assumptions of normative models of choice thatimply mechanisms of valuation sensitive to the absolute propertiesof a payoff or to expected absolute changes in state.