The role of beginner’s luck in learning to prefer risky patches by socially foraging house sparrows

Behavioral Ecology The official journal of the ISBE International Society for Behavioral Ecology Behavioral Ecology (2013), 24(6), 1398–1406. doi:10.1093/beheco/art079 Original Article The role of beginner’s luck in learning to prefer risky patches by socially foraging house sparrows Tomer Ilan,a Edith Katsnelson,b Uzi Motro,c Marcus W. Feldman,b and Arnon Lotema aDepartment of Zoology, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel, bDepartment of Biology, Stanford University, Stanford, CA 94305, USA, and cDepartment of Ecology, Evolution and Behavior, Department of Statistics, and The Center for Rationality, The Hebrew University of Jerusalem, Jerusalem 91904, Israel Received 20 November 2012; revised 24 June 2013; accepted 17 July 2013; Advance Access publication 10 September 2013 Although there has been extensive research on the evolution of individual decision making under risk (when facing variable outcomes), little is known on how the evolution of such decision-making mechanisms has been shaped by social learning and exploitation. We presented socially foraging house sparrows with a choice between scattered feeding wells in which millet seeds were hidden under 2 types of colored sand: green sand offering ~80 seeds with a probability of 0.1 (high risk–high reward) and yellow sand offering 1 seed with certainty (low risk–low reward). Although the expected benefit of choosing variable wells was 8 times higher than that of choosing constant wells, only some sparrows developed a preference for variable wells, whereas others developed a significant preference for constant wells. We found that this dichotomy could be explained by stochastic individual differences in sampling success during foraging, rather than by social foraging strategies (active searching vs. joining others). Moreover, preference for variable or constant wells was related to the sparrows’ success during searching, rather than during joining others or when picking exposed seeds (i.e., they learn when actively searching in the sand). Finally, although for many sparrows learning resulted in an apparently maladaptive risk aversion, group living still allowed them to enjoy profitable variable wells by occasionally joining variable-preferring sparrows. Key words: decision making, producer, risk sensitivity, scrounger, social foraging, social learning. Introduction Extensive research on decision making in humans and animals has focused on choices between safe and variable outcomes (e.g., Kahneman and Tversky 1979; Caraco et al. 1980; Stephens 1981; Kacelnik and Bateson 1996, 1997; Weber et al. 2004; Wu and Giraldeau 2005). In this context, the term “risk” refers to variability in reward and the term “risk sensitivity” refers to how decision makers respond to such variability. Although most earlier attempts to explain decision making under risk were based on normative models, such as those relating risk seeking or risk aversion to decelerating or accelerating utility functions (Kahneman and Tversky 1979; McNamara and Houston 1992), recent efforts have mainly focused on process-based models, which consider the mechanisms by which experience is coded and used for making further choices (e.g., March 1996; Kacelnik and Bateson 1997; Erev and Barron 2005; Shafir et al. 2008). A particular set of cases where Address correspondence to A. Lotem. E-mail: . © The Author 2013. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please e-mail: process-based models can explain phenomena such as risk aversion and underweighting of rare events is represented in reinforcement learning models (March 1996; Niv et al. 2002; Hertwig et al. 2004). For example, it has been shown that the tendency to stop exploring options that are unsuccessful (the “hot-stove effect”; Denrell and March 2001) can gradually lead to risk aversion (March 1996) and that under some conditions, learning rules may produce apparently maladaptive preference for a more assured but less profitable alternative (Erev and Barron 2005; Arbilly et al. 2010). How learning or cognitive mechanisms that produce suboptimal behavior evolve is a challenging problem. It is increasingly acknowledged that to answer this question, we need to focus on the evolution of explicit learning rules (McNamara and Houston 2009; Fawcett et al. 2012). Early work along this line suggested that a trade-off between exploration and exploitation may provide a good answer in some cases (Real 1991; Keasar 2002; Niv et al. 2002), but not in others (Kacelnik and Bateson 1996). Another direction has focused on general cognitive constraints, such as those resulting from Weber’s law or from fundamental principles of associative learning (Kacelnik and Brito e Abreu 1998; Weber Ilan et al. • Learning and risky decisions in a social context et al. 2004; Trimmer et al. 2012). These cognitive principles may prevent optimization for a particular task (or experimental test) but could have evolved to serve a much broader set of behaviors on a much larger scale of ecological conditions (see discussions by Weber et al. 2004; Trimmer et al. 2012). An alternative and more modest approach is to examine learning and decision-making mechanisms on just a slightly broader ecological scale (see e.g., Todd and Gigerenzer 2000; Stephens et al. 2004). Most of the above-mentioned research has been focused on isolated individuals making decisions under variable conditions without interacting with one another. As a result, the interaction between the learning dynamics and social foraging or social learning has received relatively little attention. An intriguing possibility, therefore, is that some of the apparently maladaptive outcomes of learning may be better understood when the social context, under which they are likely to operate in nature, is also considered. In the field of social foraging, where individuals are engaged in a frequency-dependent game between producers and scroungers (Barnard and Sibly 1981; Giraldeau and Caraco 2000; Giraldeau and Dubois 2008), explicit modeling of learning mechanisms or experimental studies of learning have just started to emerge. Most of these studies are focused on learning to choose between producer and scrounger strategies (Beauchamp 2000; Katsnelson et al. 2008; Hamblin and Giraldeau 2009; Dubois et al. 2010; MorandFerron and Giraldeau 2010; Belmaker et al. 2012; Katsnelson et al. 2012), but a few theoretical studies have explored how learning to find food in a variable environment may be affected by the social context of the producer–scrounger game (Arbilly et al. 2010, 2011). Previously, it has been suggested that group foraging is less risky (Caraco 1981) and that risk-averse individuals should scrounge more (Caraco 1981; Lendvai et al. 2004) or less (Morgan et al. 2011), but the role of learning in mediating such decisions is unclear. Similarly, e (...truncated)