Risky decisions: a test of risk sensitivity in socially foraging flocks of Lonchura punctulata

Group foraging allows for individuals to exploit the food discoveriesof other group members. If searching for food and searchingfor exploitation opportunities within a group are mutually exclusivealternatives, the decision to use one or the other is modeledas a producer-scrounger game because the value of each alternativeis frequency dependent. Stochastic producer-scrounger modelsgenerally assume that producer provides a more variable anduncertain reward than does the scrounger and hence is a riskierforaging alternative. Socially foraging animals that are attemptingto reduce their risk of starvation should therefore alter theiruse of producer and scrounger alternatives in response to changesin energy budget. We observed flocks of nutmeg mannikins (L.punctulata) foraging in an indoor aviary to determine whethertheir use of producer and scrounger alternatives were risk sensitive.Analyses of the foraging rewards of three flocks of seven birdsconfirm that producer is a riskier foraging strategy than isscrounger, although the difference in risk is rather small.We then submitted two other flocks to two different energy budgetsand observed the foraging decision of four focal birds in eachflock. All but one bird increased their relative use of theriskier producer strategy in the low food reserve treatment,but the overall use of producer did not differ significantlybetween treatments, providing evidence for a small but consistenteffect.     

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.     

The legacy effects of keystone individuals on collective behaviour scale to how long they remain within a group

The collective behaviour of social groups is often strongly influenced by one or few individuals, termed here ‘keystone individuals’. We examined whether the influence of keystone individuals on collective behaviour lingers after their departure and whether these lingering effects scale with their tenure in the group. In the social spider, Stegodyphus dumicola, colonies'' boldest individuals wield a disproportionately large influence over colony behaviour. We experimentally manipulated keystones'' tenure in laboratory-housed colonies and tracked their legacy effects on collective prey capture following their removal. We found that bolder keystones caused more aggressive collective foraging behaviour and catalysed greater inter-individual variation in boldness within their colonies. The longer keystones remained in a colony, the longer both of these effects lingered after their departure. Our data demonstrate that, long after their disappearance, keystones have large and lasting effects on social dynamics at both the individual and colony levels.     

Intertrip consistency in hunting behavior improves foraging success and efficiency in a marine top predator

Substantial variation in foraging strategies can exist within populations, even those typically regarded as generalists. Specializations arise from the consistent exploitation of a narrow behavioral, spatial or dietary niche over time, which may reduce intraspecific competition and influence adaptability to environmental change. However, few studies have investigated whether behavioral consistency confers benefits at the individual and/or population level. While still recovering from commercial sealing overexploitation, Australian fur seals (AUFS; Arctocephalus pusillus doriferus) represent the largest marine predator biomass in south‐eastern Australia. During lactation, female AUFS adopt a central‐place foraging strategy and are, thus, vulnerable to changes in prey availability. The present study investigated the population‐level repeatability and individual consistency in foraging behavior of 34 lactating female AUFS at a south‐east Australian breeding colony between 2006 and 2019. Additionally, the influence of individual‐level behavioral consistency on indices of foraging success and efficiency during benthic diving was determined. Low to moderate population‐level repeatability was observed across foraging behaviors, with the greatest repeatability in the mean bearing and modal dive depth. Individual‐level consistency was greatest for the proportion of benthic diving, total distance travelled, and trip duration. Indices of benthic foraging success and efficiency were positively influenced by consistency in the proportion of benthic diving, trip duration and dive rate but not influenced by consistency in bearing to most distal point, dive depth or foraging site fidelity. The results of the present study provide evidence of the benefits of consistency for individuals, which may have flow‐on effects at the population level.     

Behavioral interference and facilitation in the foraging cycle shape the functional response

Individual forager behaviors should affect per capita intakerates and thereby population and consumer-resource properties.We consider and incorporate conspecific facilitation and interferenceduring the separate foraging-cycle stages in a functional responsemodel that links individual behavioral interactions with consumer-resourceprocesses. Our analyses suggest that failing to properly considerand include all effects of behavioral interactions on foraging-cyclestage performances may either over- or underestimate effectsof interactions on the shape of both functional responses andpredator zero-growth isoclines. Incorporation of prey- and predator-dependentinteractions among foragers in the model produces predator isoclineswith potentials for highly complex consumer-resource dynamics.Facilitation and interference during the foraging cycle aretherefore suggested as potent behavioral mechanisms to causepatterns of community dynamics. We emphasize that correct estimationsof interaction-mediated foraging-cycle efficiencies should beconsidered in empirical and theoretical attempts to furtherour understanding of the mechanistic link between social behaviorsand higher order processes.     

Decision time modulates social foraging success in wild common ravens,Corvus corax

Social foraging provides several benefits for individuals but also bears the potential costs of higher competition. In some species, such competition arises through kleptoparasitism, that is when an animal takes food which was caught or collected by a member of its social group. Except in the context of caching, few studies have investigated how individuals avoid kleptoparasitism, which could be based on physical strength/dominance but also cognitive skills. Here, we investigated the foraging success of wild common ravens, Corvus corax, experiencing high levels of kleptoparasitism from conspecifics when snatching food from the daily feedings of captive wild boars in a game park in the Austrian Alps. Success in keeping the food depended mainly on the individuals’ age class and was positively correlated with the time to make a decision in whether to fly off with food or consume it on site. While the effect of age class suggests that dominant and/or experienced individuals are better in avoiding kleptoparasitism, the effect of decision time indicates that individuals benefit from applying cognition to such decision-making, independently of age class. We discuss our findings in the context of the ecological and social intelligence hypotheses referring to the development of cognitive abilities. We conclude that investigating which factors underline kleptoparasitism avoidance is a promising scenario to test specific predictions derived from these hypotheses.     

Social foraging: individual learning and cultural transmission of innovations

We present two stochastic models of individual and social learningthat count the number of individuals exhibiting a learned, resource-producingtrait in a group of social foragers. The novelty of our modelingresults from incorporating the empirically based assumptionthat rates of both individual and social learning should dependon the frequency of the learned trait within the group. Whenresources occur as clumps shared by group members, a naive individual'sacquisition of the skill required for clump discovery/productionshould involve opposing processes of frequency dependence. Theopportunity to learn via cultural transmission should increasewith the trait's frequency, but the opportunity for learningindividually should decrease as the trait's frequency increases.The results of the model suggest that the evolution of the capacityfor cultural transmission may be promoted in environments wherescrounging at resource clumps inhibits rates of individual learning.     

Previous agonistic experience determines both foraging behavior and territoriality in the limpet Lottia gigantea (Sowerby)

Lottia gigantea, the owl limpet, is an algal gardener. Territorial individuals actively defend gardens, which consist of clearedareas in the intertidal zone upon which a thick algal filmdevelops and upon which the territory holder feeds. Smaller,nonterritory holders raid these gardens and graze the algalfilm. Territorial individuals must obtain an adequate ration without compromising the productivity of the garden. In contrast,a nonterritory holder grazing on another limpet's territorymust obtain an adequate ration before it contacts the territoryholder and is driven off. In the laboratory, replicate setsof 10 limpets were trained to behave territorially and nonterritorially.Training mimicked natural encounters between territorial andnonterritorial L. gigantea. Limpets given territorial trainingleft significantly (t = -4.92, df = 9, p =.00041) more algalcover behind when grazing (on average 71%) than did limpetstrained to be nonterritorial (on average 50%). Territorial limpets seldom grazed over the same area more than once (4% of the grazedarea). In contrast, nonterritorial limpets frequently foragedover an area more than once; of the area grazed, 20% had beenvisited more than once. Previous agonistic experience determinesboth territorial behavior and foraging strategies, two of thecritical behaviors necessary for successful gardening behavior.Nonterritorial limpets maximize consumption per unit area, whereas territorial limpets appear to forage prudently, leaving a significantly greater proportion of the plant biomass behind.     

The role of conformity in foraging when personal and social information conflict

There is currently considerable interest in the interplay betweenpersonal and social information in decision-making processes.Two experiments are presented exploring the relative use ofprior personal information and subsequent social informationin foraging decisions of guppies. Experiment 1 tested the assumptionthat when the use of information acquired through personal experienceis not costly, conflicting social information will be ignored.The assumption was confirmed because, when given a choice betweenfeeding at two food patches, at one of which they had previouslyseen conspecifics feed, individual fish with prior experienceof feeding at the alternative site chose the alternative, whereasfish with no prior experience chose the site at which theirconspecifics had fed. Experiment 2 tested theoretical predictionsthat when the use of information acquired through personal experienceis potentially costly, conflicting social information will beweighed more heavily than will personal information. The predictionwas confirmed because, when given a choice between feeding attwo food patches, one at which they had previously seen conspecificsfeed and one behind a visual barrier, individual fish with priorexperience of feeding behind the barrier chose the site at whichtheir conspecifics had fed. These findings suggest that conformitycan promote social learning in naïve individuals, but priorexperience can insulate individuals from conformity providedthe costs of relying on that experience are small. In addition,the experiments highlight the fact that personal and socialinformation are not always weighed equally.     

Plant structure and the foraging success of Aphidius rhopalosiphi (Hymenoptera: Aphidiidae)

Abstract. 1. A study of searching behaviour on wheat and host preference of Aphidius rhopalosiphi (DeStefani-Perez) is described.
2. Parasitoids divided their time equally between the leaves but spent very little time on the ear.
3. After contact with honeydew or an aphid host, parasitoids were arrested in a particular area and increased the time spent searching.
4. Aphids feeding on the ear were parasitized less successfully, since their position between the grains protected them from parasitoid attacks.
5. A.rhopalosiphi exhibited no preference for Metopolophium dirhodum (Walker) or Sitobion avenae (Fabricius), although the handling time for the latter was significantly longer; this resulted in fewer S.avenae being parasitized when it was abundant. Parasitoids did not switch between hosts in these experiments.
6. As a result of its searching behaviour, A.rhopalosiphi will encounter and parasitize M.dirhodum feeding on the leaves more frequently than S.avenae, which feeds on the ear. This will limit the parasitoid's ability to regulate populations of the cereal aphid S. avenae.     

Previous foraging success influences web building in the spider Stegodyphus lineatus (Eresidae)

Stegodyphus lineatus (Eresidae) is a desert spider that buildsan aerial capture web on bushes in the Negev desert in southernIsrael. Web building for spiders is costly in energy, time,and risk of predation. Spiders should trade-off these costswith the benefits in terms of prey capture. We tested the hypothesisthat the previous foraging success of the spider influencesthe effort invested in foraging. Specifically, we asked whetheran increase in food intake causes spiders to reduce web renewalactivity and web size. Alternatively, time constraints on foragingand development, resulting from a short growing season, couldinduce spiders to continue foraging even when supplemented withprey. The cost of web building was measured as time and massloss. To build an average size web (about 150 cm²), we calculatedthat a spider requires 6 h and that spiders lose 3%-7% of their weight.In field experiments, spiders responded differently to food supplementationin 2 different years. In 1994, they improved their condition comparedto individuals whose webs were removed to reduce foraging opportunitiesand compared to control spiders. In 1995, spiders tested earlier inthe season than the previous year did not improve their conditionin response to prey supplementation. Nonetheless, in both years, food-supplementedspiders built significantly smaller webs than food-deprived andcontrol spiders. This result was confirmed in a laboratory experiment whereprey intake was controlled. We conclude that for S. lineatus immediateforaging risks outweigh the potential time constraints on foraging.     

Plastic proteans: reduced predictability in the face of predation risk in hermit crabs

Variation in behaviour occurs at multiple levels, including between individuals (personality) and between situations (plasticity). Behaviour also varies within individuals, and intra-individual variation (IIV) in behaviour describes within-individual residual variance in behaviour that remains after the effects of obvious external and internal influences on behaviour have been accounted for. IIV thus describes how predictable an individual''s behaviour is. Differences in predictability, between individuals and between situations, might be biologically significant. For example, behaving unpredictably under predation threat might reduce the chance of capture. Here, we investigated the duration of startle responses in hermit crabs, in the presence and absence of a predator cue. Individuals differed in startle response duration (personality) and while individuals also varied in their sensitivity to risk, mean response time was greater in the presence of a predator (plasticity). Moreover, IIV was greater in the presence of a predator, providing some of the first evidence that the facultative injection of unpredictability into behaviour might represent a strategy for dealing with risk.     

Spatial and temporal variation in pheromone composition of ant foraging trails

Many social insects use pheromones to communicate and coordinatetheir activities. Investigation of intraspecific differencesin pheromone use is a new area of social insect research. Forexample, interindividual variation in alarm pheromone contenthas been found in physical castes of polymorphic ants. Manyant species use multiple trail pheromones. Here we present novelresearch into trail pheromone variations between behavioralsubcastes of pharaoh ants, Monomorium pharaonis. Monomoriumpharaonis is attracted to trail pheromones found in its poisonglands (monomorines) and Dufour's glands (faranal). We showthat the most abundant monomorines, I (M1) and III (M3), canbe readily detected in pheromone trails. A behaviorally distinctsubcaste known as "pathfinder" foragers can relocate long-livedpheromone trails. Chemical analysis showed that pathfinder foragershad low M3:M1 ratios (mean 3.09 ± 1.53, range 1.03–7.10).Nonpathfinder foragers had significantly greater M3:M1 ratios(38.3 ± 60.0, range 3.54–289). We found that M3:M1ratio did not differ between foragers of different age but wascorrelated with behavioral subcaste at all ages. The relativeabundance of M3:M1 on foraging trails ranged from 3.03–41.3over time during pheromone trail build-up. M3:M1 ratio alsovaried spatially throughout trail networks, being lowest ontrail sections closest to a food source (M3:M1 = 1.9–3.61)and highest near the nest (M3:M1 = 67–267). Our resultsindicate a functional role for differences in pheromone trailcomposition, whereby pathfinder foragers might preferentiallymark sections of pheromone trail networks for future exploration.     

The development of foraging microhabitat preferences in meerkats

Animals of many species tend to target their foraging attemptstoward particular microhabitats within their habitat. Althoughthese preferences are critical determinants of the foragingniche and have important ecological and evolutionary implications,we know little about how they develop. Here, we use detailedlongitudinal data from meerkats (Suricata suricatta) to examinehow individual learning and the use of social information affectthe development of foraging microhabitat preferences. Despiteliving in an open, arid environment, adult meerkats frequentlyforaged at the base of vegetation. Young pups seldom did so,but their foraging microhabitat choices became increasinglyadult-like as they grew older. Learning about profitable microhabitatsmay have been promoted in part by positive reinforcement fromprey capture. Foraging may also have become increasingly targetedtoward suitable locations as pups grew older because they spentmore time searching before embarking on foraging bouts. Thedevelopment of microhabitat preferences might also have beeninfluenced by social cues. Foraging in close proximity to adultsmay increase the probability that pups would dig in similarmicrohabitats. Also, pups often dug in holes created by olderindividuals, whereas adults never dug in existing holes. Foragingin existing holes was no more profitable to pups than creatingtheir own foraging hole but could provide pups with importantinformational benefits. The integration of personal and socialinformation is likely to be a common feature in the developmentof the foraging niche in generalist species.