Luc-Alain Giraldeau

Producers, scroungers, and group foraging

We have developed a model that reconciles information-sharing and producer-scrounger models of group foraging. Our model includes producers, scroungers, and an opportunistic forager that can both produce and scrounge but with reduced efficiency. We show that these three strategies can coexist only in the unlikely case that the opportunists loss in searching ability is exactly equal to its gain in scrounging ability. However, all pairs of strategies can coexist. Three parameters control the proportions of coexisting strategists: the degree of compatibility between the opportunists producing and scrounging activities; the proportion of food patches that are shared with scrounging individuals; and the effective group size. When there is little incompatibility between producing and scrounging, opportunists will always be present, unless the producer is able to consume most of the patch without sharing. The opportunist strategy is always excluded when there is a high degree of incompatibility between producing and scrounging. We consider the organismal and ecological factors that are likely to affect all three parameters. Our model predicts that scrounging behavior is likely to be selected in a wide range of foraging groups and that it may impose a considerable cost on sociality.

Neighbours, strangers, and the asymmetric war of attrition

Abstract The literature showing that territorial residents generally respond more intensely to an intrusion by a stranger than by a known neighbour is reviewed. The functional basis of this discrimination has not been seriously considered in this extensive literature, and it is shown here how the asymmetric war of attrition can explain why neighbours settle with relatively little aggression. In the asymmetric war-of-attrition model the degree of escalation observed in a territorial contest depends on the familiarity of the contestants with each other. Predictions of this model about neighbour-stranger contests are supported by data in the literature.

Scrounging prevents cultural transmission of food-finding behaviour in pigeons

Abstract Living in groups should promote the cultural transmission of a novel behaviour because opportunities for observing knowledgeable individuals are likely to be more numerous in this condition. However, in this study pigeons who shared the food discoveries of others (scroungers) did not learn the food-finding technique used by the discoverers (producers). Individually-caged pigeons prevented from scrounging easily learned the technique from a conspecific tutor. When caged pigeons obtained food from the tutors performance, most naive observers failed to learn. In a flock, scroungers selectively followed producers. In individual cages, scrounging during the tutors demonstration was equivalent to getting no demonstration at all. This effect of scrounging did not interfere with subsequent acquisition of the food-finding behaviour when scrounging was no longer possible.

Inadvertent social information in breeding site selection of natal dispersing birds

Several species use the number of young produced as public information (PI) to assess breeding site quality. PI is inaccessible for synchronously breeding birds because nests are empty by the time the young can collect this information. We investigate if location cues are the next best source of inadvertent social information (ISI) used by young prospectors during breeding site choice. We experimentally deployed ISI as decoys and song playbacks of breeding males in suitable and sub-optimal habitats during pre- and post-breeding periods, and monitored territory establishment during the subsequent breeding season for a social, bobolink (Dolichonyx oryzivorus), and a more solitary species, Nelsons sharp-tailed sparrow (Ammodramus nelsoni). The sparrows did not respond to treatments, but bobolinks responded strongly to post-breeding location cues, irrespective of habitat quality. The following year, 17/20 sub-optimal plots to which bobolink males were recruited were defended for at least two weeks, indicating that song heard the previous year could exert a ‘carry-over attraction’ effect on conspecifics the following year. Sixteen recruited males were natal dispersers, as expected when animals have little opportunity to directly sample their natal habitat quality. We suggest that differences in breeding synchronicity may induce an equivalent clinal distribution of ISI use.

Vicarious sampling: The use of personal and public information by starlings foraging in a simple patchy environment

Abstract Group foragers may be able to assess patch quality more efficiently by paying attention to the sampling activities of conspecifics foraging in the same patch. In a previous field experiment, we showed that starlings foraging on patches of hidden food could use the successful foraging activities of others to help them assess patch quality. In order to determine whether a starling could also use another individual’s lack of foraging success to assess and depart from empty patches more quickly, we carried out two experimental studies which compared the behaviour of captive starlings sampling artificial patches both when alone and when in pairs. Solitary starlings were first trained to assess patch quality in our experimental two-patch system, and were then tested on an empty patch both alone and with two types of partner bird. One partner sampled very few holes and thus provided a low amount of public information; the other sampled numerous holes and thus provided a high amount of public information. In experiment 1, we found no evidence of vicarious sampling. Subjects sampled a similar number of empty holes when alone as when with the low and high information partners; thus they continued to rely on their own personal information to make their patch departure decisions. In experiment 2, we modified the experimental patches, increasing the ease with which a bird could watch another’s sampling activities, and increasing the difficulty of acquiring accurate personal sampling information. This time, subjects apparently did use public information, sampling fewer empty holes before departure when with the high-information partner than when with the low-information partner, and sampling fewer holes when with the low-information partner than when alone. We suggest that the degree to which personal and public information are used is likely to depend both on a forager’s ability to remember where it has already sampled and on the type of environment in which foraging takes place.

Exploring the costs and benefits of social information use: an appraisal of current experimental evidence

Research on social learning has focused traditionally on whether animals possess the cognitive ability to learn novel motor patterns from tutors. More recently, social learning has included the use of others as sources of inadvertent social information. This type of social learning seems more taxonomically widespread and its use can more readily be approached as an economic decision. Social sampling information, however, can be tricky to use and calls for a more lucid appraisal of its costs. In this four-part review, we address these costs. Firstly, we address the possibility that only a fraction of group members are actually providing social information at any one time. Secondly, we review experimental research which shows that animals are circumspect about social information use. Thirdly, we consider the cases where social information can lead to incorrect decisions and finally, we review studies investigating the effect of social information quality. We address the possibility that using social information or not is not a binary decision and present results of a study showing that nutmeg mannikins combine both sources of information, a condition that can lead to the establishment of informational cascades. We discuss the importance of empirically investigating the economics of social information use.

Song complexity correlates with learning ability in zebra finch males.

In species with mate choice, the choosy sex selects its mate based on traits that are thought to indicate the mates quality. In several bird species, females prefer males that sing more complex songs but it is unclear which aspect of male quality is signalled by this trait. Here we tested the hypothesis that a males song complexity conveys information about his learning capacity. We recorded the songs of 27 male zebra finches, Taeniopygia guttata, and quantified their complexity by measuring average song phrase duration, the total number of elements and the number of unique elements per song phrase. We then presented each male with a novel foraging task and recorded the number of trials he required to solve the task. We found a positive correlation between song complexity and learning proficiency: males with more song phrase elements required fewer learning trials to solve the novel foraging task. This result suggests that a males song complexity signals his learning ability, which may have contributed to the selective pressures driving females to choose males with more complex songs.

Exchangeable producer and scrounger roles in a captive flock of feral pigeons: a case for the skill pool effect

We investigated the foraging producer-scrounger system of a captive flock of feral pigeons (Columba livia) by monitoring the number of food patches each individual produced. In one experiment, three different patch types were tested on the whole flock while, in a second, flock composition was varied for one patch type. In all cases we found non-uniform distributions of the number of patches produced per individual, which suggests the existence of producer and scrounger roles. This result could not be explained by either dominance or variability in individual learning ability. Individuals switched roles in response to changes both in food patch type and flock composition. These results are discussed in light of the skill pool hypothesis, which suggests that, in a group, different foraging specialists will profit by parasitizing each others food discoveries.

Influence of Conspecific Attraction on the Spatial Distribution of Learning Foragers in a Patchy Habitat

1. Individuals in many social species are attracted to feeding conspecifics. The profitability of conspecific attraction is negatively frequency-dependent and can be modelled as a producer-scrounger (PS) game for which the ESS solution predicts some mixture of producer (no attraction) and scrounger (attraction) tactics in the population. Current models for the spatial distribution of rate-maximizing foragers, which learn the quality of habitats as they exploit patches, ignore the possible effect of conspecific attraction on the stable distribution of foragers. 2, We used simulations of a population with ESS levels of attraction to investigate the effect of conspecific attraction on the spatial distribution of learning foragers which incur travel costs. In habitats where patches depleted slowly, ESS levels of attraction helped foragers which experienced no interference reach the expected ideal free distribution (IFD) by facilitating aggregation to the richest patches. Large aggregations also occurred with interference and thus reduced the fit to the IFD, which in this case predicts a scatter of foragers across patches of varying quality. 3. In habitats where patches depleted rapidly, ESS levels of attraction prevented foragers from reaching the IFD, irrespective of interference levels. Foragers failed to learn habitat quality and thus often aggregated in poor patches, especially in large populations which depleted patches faster and had fewer opportunities to learn quality. 4. Predictions of the model in habitats where patches deplete slowly are supported by several studies. More work is needed for habitats where patches deplete more rapidly. We conclude that conspecific attraction can have important, and often disruptive effects on spatial distributions.

GROUP FORAGING: THE SKILL POOL EFFECT AND FREQUENCY-DEPENDENT LEARNING

It is hypothesized that mixed-species foraging aggregations provide each individual with a wider range of food items as a result of social learning and the diversity of foraging specializations among species (Krebs 1973). I hypothesize that the skill pool effect should provide similar benefits to single-species foraging groups without social learning. The skill pool occurs when different foraging specialists join the discoveries of others. While providing an increased range of food items, it permits increased individual foraging efficiency through specialization. When individual learning is important in the development of foraging behaviors, it should generate frequency-dependent effects which promote individual specializations favoring the occurrence of skill pools. From the skill pool effect several ecological and behavioral predictions are generated that require more attention to comparisons of individual diets and behaviors inside and outside foraging groups.