Does Foraging Behaviour Affect Female Mate Preferences and Pair Formation in Captive Zebra Finches?

Background

Successful foraging is essential for survival and reproductive success. In many bird species, foraging is a learned behaviour. To cope with environmental change and survive periods in which regular foods are scarce, the ability to solve novel foraging problems by learning new foraging techniques can be crucial. Although females have been shown to prefer more efficient foragers, the effect of males'' foraging techniques on female mate choice has never been studied. We tested whether females would prefer males showing the same learned foraging technique as they had been exposed to as juveniles, or whether females would prefer males that showed a complementary foraging technique.

Methodology/Principal Findings

We first trained juvenile male and female zebra finches (Taeniopygia guttata) to obtain a significant proportion of their food by one of two foraging techniques. We then tested whether females showed a preference for males with the same or the alternative technique. We found that neither a male''s foraging technique nor his foraging performance affected the time females spent in his proximity in the mate-choice apparatus. We then released flocks of these finches into an aviary to investigate whether assortative pairing would be facilitated by birds taught the same technique exploiting the same habitat. Zebra finches trained as juveniles in a specific foraging technique maintained their foraging specialisation in the aviary as adults. However, pair formation and nest location were random with regard to foraging technique.

Conclusions/Significance

Our findings show that zebra finches can be successfully trained to be foraging specialists. However, the robust negative results of the conditions tested here suggest that learned foraging specializations do not affect mate choice or pair formation in our experimental context.     

Frequency-dependent payoffs and sequential decision-making favour consistent tactic use

Although natural selection should have favoured individuals capable of adjusting the weight they give to personal and social information according to circumstances, individuals generally differ consistently in their individual weighting of both types of information. Such individual differences are correlated with personality traits, suggesting that personality could directly affect individuals' ability to collect personal or social information. Alternatively, the link between personality and information use could simply emerge as a by-product of the sequential decision-making process in a frequency-dependent context. Indeed, when the gains associated with behavioural options depend on the choices of others, an individual's sequence of arrival could constrain its choice of options leading to the emergence of correlated behaviours. Any factor such as personality that affects decision order could thus be correlated with information use. To test this new explanation, we developed an individual-based model that simulates a group of animals engaged in a game of sequential frequency-dependent decision: a producer-scrounger game. Our results confirm that the sequence of decision, in this case enforced by the order in which animals enter a foraging area, consistently influences their mean tactic use and their individual plasticity, an outcome reminiscent of the correlation reported between personality and social information use.     

The effect of patch size and competitor number on aggression among foraging house sparrows

We examined the effect of patch size and competitor number onaggression among house sparrows, Passer domesticus, foragingat patches of seven different sizes in a doubling series (0.014,0.029, 0.058, 0.116, 0.230, 0.462, and 0.922 m²). Contrary toour expectations, the birds did not defend an entire patch,even when it was small as 0.014 m². The frequency of aggressionamong the birds decreased gradually with increasing patch size,in contrast to the step decline predicted by resource defensetheory. Moreover, the birds fought more frequently and moreintensely as competitor density increased. Both results areconsistent with the predictions of a modified hawk-dove modelfor shared patches. Females were more aggressive and fed ata higher rate than did males. The proportion of females increasedas patch size decreased, and aggression became more frequentand intense. Even when patches are shared, patch size has animportant effect on the frequency and intensity of foragingcompetition and the size and composition of foraging groups.     

Social influences on foraging in vertebrates: causal mechanisms and adaptive functions

We summarize 20 years of empirical and theoretical research on causes and functions of social influences on foraging by animals. We consider separately studies of social influence on when, where, what and how to eat. Implicit in discussion of the majority of studies is our assumption that social influences on foraging reflect a biasing of individual learning processes by social stimuli rather than action of independent social-learning mechanisms. Our review of theoretical approaches suggests that the majority of formally derived hypotheses concerning functions of social influence on foraging have not yet been tested adequately and many models are in need of further refinement. We also consider the importance to the future of the field of integrating 'top-down' and 'bottom-up' approaches to the study of social learning. Copyright 2001 The Association for the Study of Animal Behaviour.     

The forager's dilemma: food sharing and food defense as risk-sensitive foraging options

Although many variants of the hawk-dove game predict the frequency at which group foraging animals should compete aggressively, none of them can explain why a large number of group foraging animals share food clumps without any overt aggression. One reason for this shortcoming is that hawk-dove games typically consider only a single contest, while most group foraging situations involve opponents that interact repeatedly over discovered food clumps. The present iterated hawk-dove game predicts that in situations that are analogous to a prisoner's dilemma, animals should share the resources without aggression, provided that the number of simultaneously available food clumps is sufficiently large and the number of competitors is relatively small. However, given that the expected gain of an aggressive animal is more variable than the gain expected by nonaggressive individuals, the predicted effect of the number of food items in a clump-clump richness-depends on whether only the mean or both the mean and variability associated with payoffs are considered. More precisely, the deterministic game predicts that aggression should increase with clump richness, whereas the stochastic risk-sensitive game predicts that the frequency of encounters resulting in aggression should peak at intermediate clump richnesses or decrease with increasing clump richness if animals show sensitivity to the variance or coefficient of variation, respectively.     

Increasing vulnerability to predation increases preference for the scrounger foraging tactic

When animals forage in groups, individuals can search for foodthemselves (producer tactic) or they can search for and joinother individuals that have located food (scrounger tactic).The scrounger tactic may provide greater antipredator benefitsthan the producer tactic because "scroungers" hop with theirheads up and tend to occupy central positions in a group, whereas"producers" hop with their heads down and tend to occupy edgepositions. We tested whether increasing an individual's vulnerabilityto predation (using wing-loading manipulations) causes an increasedpreference for the scrounger tactic in zebra finches (Taeniopygiaguttata). Wing-loading manipulations were effective at increasingfocal individuals' perception of vulnerability to predation;treatment individuals increased their total time allocated tovigilance, whereas control individuals did not. Treatment individualsalso increased their use of the scrounger tactic (proportionof hops with head up) and scrounged a greater proportion ofpatches, whereas control individuals exhibited no changes. Ourresults are consistent with the hypothesis that the scroungertactic confers greater antipredator benefits than the producertactic, although whether antipredator benefits are achievedthrough differences in head orientation, spatial position, orboth, remains unclear. Our finding that individuals adjust theiruse of the scrounger tactic according to changes in their phenotypeprovides evidence for phenotype-limited allocation strategiesin producer–scrounger games.     

Individual differences in plasticity and sampling when playing behavioural games

When engaged in behavioural games, animals can adjust their use of alternative tactics until groups reach stable equilibria. Recent theory on behavioural plasticity in games predicts that individuals should differ in their plasticity or responsiveness and hence in their degree of behavioural adjustment. Moreover, individuals are predicted to be consistent in their plasticity within and across biological contexts. These predictions have yet to be tested empirically and so we examine the behavioural adjustment of individual nutmeg mannikins (Lonchura punctulata), gregarious ground-feeding passerines, when playing two different social foraging games: producer-scrounger (PS) and patch-choice (PC) games. We found: (i) significant individual differences in plasticity and sampling behaviour in each of the two games, (ii) individual differences in sampling behaviour were consistent over different test conditions within a game (PC) and over a six month period (PS), (iii) but neither individual plasticity nor sampling behaviour was correlated from one social foraging game to another. The rate at which birds sampled alternative tactics was positively associated with seed intake in PS trials but negatively associated in PC trials. These results suggest that games with frequency dependence of pay-offs can maintain differences in behavioural plasticity but that an important component of this plasticity is group- and/or context-specific.