We examined how starlings, Sturnus vulgaris, adjust preferences to retrospective sunk costs in either time or work. Ideal decision-makers disregard sunk costs, but under some circumstances animals, like humans, prefer normally costlier rewards when they do not have to pay the costs. We argue that a possible explanation is state-dependent valuation learning (SDVL). The argument is that subjective value (hedonic state or fitness) is a decelerated function of energetic state, and energetic costs...