Context-dependent foraging choices in risk-sensitive starlings

Existing models of risk-sensitive foraging assume that animals assign value to different options according to an absolute currency. It follows from this assumption that choices are expected to be both transitive and regular, because the value assigned to an option is independent of its context. I tested these predictions by comparing preferences obtained in binary and trinary contexts. European starlings, Sturnus vulgaris, were trained using an operant paradigm to forage for three options: Constant (C) that provided a fixed number of food pellets; Low variance (L) with a coefficient of variation of 71% in the number of pellets; High variance (H) with a coefficient of variation of 106%. The preferences of the birds were tested in three binary choice treatments (CL, CH, LH) and one trinary choice treatment (CLH). Overall, there was no evidence for violations of either transitivity or regularity. However, overall, a bird's relative preference for its most preferred option over its second most preferred option was significantly greater in the trinary treatment than in the comparable binary treatment. This effect of context on choice is compatible with starlings' use of comparative instead of absolute currencies in decision making. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.