Context-dependent preferences in starlings: linking ecology, foraging and choice

Foraging animals typically encounter opportunities that they either pursue or skip, but occasionally meet several alternatives simultaneously. Behavioural ecologists predict preferences using absolute properties of each option, while decision theorists focus on relative evaluations at the time of choice. We use European starlings (Sturnus vulgaris) to integrate ecological reasoning with decision models, linking and testing hypotheses for value acquisition and choice mechanism. We hypothesise that options' values depend jointly on absolute attributes, learning context, and subject's state. In simultaneous choices, preference could result either from comparing subjective values using deliberation time, or from processing each alternative independently, without relative comparisons. The combination of the value acquisition hypothesis and independent processing at choice time has been called the Sequential Choice Model. We test this model with options equated in absolute properties to exclude the possibility of preference being built at the time of choice. Starlings learned to obtain food by responding to four stimuli in two contexts. In context [AB], they encountered options A5 or B10 in random alternation; in context [CD], they met C10 or D20. Delay to food is denoted, in seconds, by the suffixes. Observed latency to respond (Li) to each option alone (our measure of value) ranked thus: LA≈LC<LB<<LD, consistently with value being sensitive to both delay and learning context. We then introduced simultaneous presentations of A5 vs. C10 and B10 vs. C10, using latencies in no-choice tests to predict sign and strength of preference in pairings. Starlings preferred A5 over C10 and C10 over B10. There was no detectable evaluation time, and preference magnitude was predictable from latency differentials. This implies that value reflects learning rather than choice context, that preferences are not constructed by relative judgements at the time of choice, and that mechanisms adapted for sequential decisions are effective to predict choice behaviour.This work was supported by Biotechnology and Biological Sciences Research Council (BBSRC) Grant BB/G007144/1 to AK www.bbsrc.ac.uk; TM was supported by a Doctoral Grant from the Portuguese Foundation for Science and Technology (FCT) www.fct.pt/index.phtml.en. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Fluctuating Environments, Sexual Selection and the Evolution of Flexible Mate Choice in Birds

Environmentally-induced fluctuation in the form and strength of natural selection can drive the evolution of morphology, physiology, and behavior. Here we test the idea that fluctuating climatic conditions may also influence the process of sexual selection by inducing unexpected reversals in the relative quality or sexual attractiveness of potential breeding partners. Although this phenomenon, known as ‘ecological cross-over’, has been documented in a variety of species, it remains unclear the extent to which it has driven the evolution of major interspecific differences in reproductive behavior. We show that after controlling for potentially influential life history and demographic variables, there are significant positive associations between the variability and predictability of annual climatic cycles and the prevalence of infidelity and divorce within populations of a taxonomically diverse array of socially monogamous birds. Our results are consistent with the hypothesis that environmental factors have shaped the evolution of reproductive flexibility and suggest that in the absence of severe time constraints, secondary mate choice behaviors can help prevent, correct, or minimize the negative consequences of ecological cross-overs. Our findings also illustrate how a basic evolutionary process like sexual selection is susceptible to the increasing variability and unpredictability of climatic conditions that is resulting from climate change

Rationality in risk-sensitive foraging choices by starlings

Normative models of choice usually predict preferences between alternatives by computing their value according to some criterion, then identifying the alternative with greatest value. An important consequence of this procedure is captured in the economic concept of rationality, defined through a number of principles that are necessary for the existence of an ordinal scale of value upon which organisms base their choices. Violations of these principles, such as some recently reported breaches of transitivity and regularity in birds and honeybees, have strong implications for the understanding of decision mechanisms in humans and nonhumans alike. We investigated rationality in risky choice using European starlings, Sturnus vulgaris. Birds had to choose between two or three food sources, each associated with a different variance in delay to reward. In three experiments, starlings were strongly risk prone, showing regular and consistent preferences in binary and trinary choices. Preferences also satisfied weak and strong stochastic transitivity. Our results extend the generality of previous research in risk-sensitive foraging to situations where more than two alternatives are present and suggest that violations of rationality in risk-sensitive choices may be expressed only under restricted sets of conditions. © 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved

Risk sensitivity for amounts of and delay to rewards: adaptation for uncertainty or by-product of reward rate maximising?

Observations that humans and other species are sensitive to variability in the outcome of their choices has led to the widespread assumption that this sensitivity reflects adaptations to cope with risk (stochasticity of action consequences). We question this assumption in experiments with starlings. We show that choices between outcomes that are risky in both amount and delay to food are predictable from preferences in the absence of risk. We find that the overarching best predictor of an option's value is the average of the ratios of amount to delay across its (frequency weighted) outcomes, an expression known as "Expectation of the Ratios", or EoR. Most tests of risk sensitivity focus on the predicted impact of energetic state on preference for risk. We show instead that under controlled state conditions subjects are variance- and risk-neutral with respect to EoR, and this implies variance neutrality for amounts and variance-proneness for delays. The weak risk aversion for amounts often reported requires a small modification of EoR. EoR is consistent with associative learning: acquisition of value for initially neutral stimuli is roughly proportional to the magnitude of their consequences and inversely proportional to the interval between the stimulus and its consequence's onset. If, as is likely, the effect of amount on acquisition is sublinear, the result is a deviation from EoR towards risk aversion for amount. In 3 experiments, we first establish individual birds' preferences between pairs of fixed options that differ in both amount and delay (small-sooner vs. large-later), and then examine choices between stochastic mixtures that include these options. Experiment 1 uses a titration to establish certainty equivalents, while experiments 2 and 3 measure degree of preference between options with static parameters. The mixtures differ in the coefficient of variation of amount, delay, or both, but EoR is sufficient to predict all results, with no additional explanatory role for riskiness