Can information sharing explain recruitment to food from communal roosts?

The debate over whether communal nests and roosts function primarilyas information centers (they facilitate the sharing of foraginginformation) remains unresolved. Here I use evolutionary gametheory to investigate the relative importance of this influentialhypothesis and an alternative: that roosts, in particular,function as recruitment centers (they facilitate aggregationat food patches). Basing my model on juvenile common raven (Corvus corax) behavior, I assume there is no net cost to beingat food patches in groups, and foragers roost communally. Moreover,one strategic outcome is the observed raven behavior: individualssearch independently and recruit from the roost once a patchis found (they play Search-and-Recruit, or SR). I investigatethe stability of this in two scenarios that differ in the magnitudeof the lost opportunity costs to mutants playing SR in populations of other strategies. When these costs only involve a chanceof not being in a group at a located carcass, SR is the onlyevolutionarily stable strategy under all conditions. However,when these costs also include missing opportunities to be sociallydominant, SR no longer enjoys exclusive dominance in the strategyset. Nevertheless, in both cases, there are conditions where group foraging benefits have no effect on the evolutionary stabilityof SR. Thus, contrary to assertions in the literature, theopportunity to share foraging information can be sufficientto drive the evolution and maintenance of recruitment to foodfrom communal roosts. However, I conclude that both informationand grouping benefits are likely to underlie communal roostingbehavior in my focal system.     

The benefit of being a social butterfly: communal roosting deters predation

Aposematic passion-vine butterflies from the genus Heliconius form communal roosts on a nightly basis. This behaviour has been hypothesized to be beneficial in terms of information sharing and/or anti-predator defence. To better understand the adaptive value of communal roosting, we tested these two hypotheses in field studies. The information-sharing hypothesis was addressed by examining following behaviour of butterflies departing from natural roosts. We found no evidence of roost mates following one another to resources, thus providing no support for this hypothesis. The anti-predator defence hypothesis was tested using avian-indiscriminable Heliconius erato models placed singly and in aggregations at field sites. A significantly higher number of predation attempts were observed on solitary models versus aggregations of models. This relationship between aggregation size and attack rate suggests that communally roosting butterflies enjoy the benefits of both overall decreased attack frequency as well as a prey dilution effect. Communal roosts probably deter predators through collective aposematism in which aggregations of conspicuous, unpalatable prey communicate a more effective repel signal to predators. On the basis of our results, we propose that predation by birds is a key selective pressure maintaining Heliconius communal roosting behaviour.     

Common Myna Roosts Are Not Recruitment Centres

We studied communal roosting in the Common Myna (Acridotheres tristis) in the light of the recruitment centre hypothesis and predation at the roost. The number and sizes of flocks departing from and arriving at focal roosts were recorded over a two year period. We also recorded the sizes and behaviour of foraging flocks. We found that flock sizes of birds departing from roosts at sunrise were larger than those at the feeding site, suggesting that there was no recruitment from the roosts. Flocks entering the roosts during sunset were larger on average than those leaving the following sunrise, suggesting no consolidation of flocks in the morning. Flocks entering the roosts at sunset were also larger on average than those that had left that sunrise, although there was no recruitment at the feeding site. There was no effect of group size on the proportion of time spent feeding. Contrary to expectation, single birds showed lower apparent vigilance than birds that foraged in pairs or groups, possibly due to scrounging tactics being used in the presence of feeding companions. Thus, the recruitment centre hypothesis did not hold in our study population of mynas. Predation at dawn and dusk were also not important to communal roosting: predators near the roosts did not result in larger flocks, and resulted in larger durations of arrival/departure contrary to expectation. Since flock sizes were smallest at the feeding site and larger in the evening than in the morning, but did not coincide with predator activity, information transfer unrelated to food (such as breeding opportunities) may possibly give rise to the evening aggregations.     

The selfish nature of generosity: harassment and food sharing in primates

Animals may share food to gain immediate or delayed fitness benefits. Previous studies of sharing have concentrated on delayed benefits such as reciprocity, trade and punishment. This study tests an alternative model (the harassment or sharing-under-pressure hypothesis) in which a food owner immediately benefits because sharing avoids costly harassment from a beggar. I present an experiment that varies the potential ability of the beggar to harass, and of the owner to defend the food, to examine the effects of harassment on food sharing in two primate species: chimpanzees (Pan troglodytes) and squirrel monkeys (Saimiri boliviensis). For both species, high levels of harassment potential significantly increased both beggar harassment and sharing by the owner. Food defensibility did not affect harassment or sharing. Interestingly, squirrel monkeys and chimpanzees shared equally frequently with conspecifics despite a much higher natural sharing rate in chimpanzees. These results suggest that harassment can play a significant role in primate food sharing, providing a simple alternative to reciprocity. The selfish nature of harassment has implications for economic, psychological and evolutionary studies of cooperative systems.     

Social grooming in the common vampire bat,Desmodus rotundus

Grooming patterns among 65 common vampire bats in hollow tree day roosts were studied by behavioural sampling techniques during a 15-month period. Self-grooming occurred more than social grooming in response to ectoparasites since the proportion of time spent self-grooming and the amount of ectoparasite infestation covaried positively among tree roosts while the time spent grooming others was independent of roots and ectoparasite level. Rates of social grooming were not independent of the sex of participants due to infrequent social grooming by adult males. Two variables, the level of relatedness and a measure of roosting association, which previously were shown to predict food sharing by regurgitation, correlated positively with the rate of social grooming. Since social grooming occurred more often than expected before a regurgitation and correlated with regurgitation frequency, it is suggested that this behaviour facilitates identification of food sharing partners by enabling a grooming bat to monitor other animals' potential for giving or receiving blood.     

A conceptual framework for nonkin food sharing: timing and currency of benefits

Many animal species, from arthropods to apes, share food. This paper presents a new framework that categorizes nonkin food sharing according to two axes: (1) the interval between sharing and receiving the benefits of sharing, and (2) the currency units in which benefits accrue to the sharer (especially food versus nonfood). Sharers can obtain immediate benefits from increased foraging efficiency, predation avoidance, mate provisioning, or manipulative mutualism. Reciprocity, trade, status enhancement and group augmentation can delay benefits. When benefits are delayed or when food is exchanged for nonfood benefits, maintaining sharing can become more difficult because animals face discounting and currency conversion problems. Explanations that involve delayed or nonfood benefits may require specialized adaptations to account for timing and currency-exchange problems. The immediate, selfish fitness benefits that a sharer may gain through by-product or manipulative mutualism, however, apply to various food-sharing situations across many species and may provide a simpler, more general explanation of sharing.     

High surface temperatures select for individual foraging in ants

Natural selection favors signals, receptors, and signaling behaviorthat maximize the received signal relative to background noiseand that minimize signal degradation. The physical propertiesof the environment affect rates of attenuation and degradationof the signal, and thus temperature may influence the evolutionand maintenance of volatile chemical signals. We tested this hypothesis in ants, where nest mate recruitment to a food sourceby laying trail pheromones on a surface is a common phenomenon.We collected data on maximal soil surface temperatures duringthe ants' activity and mode of foraging (recruitment or solitary).By using two different comparative methodologies, we demonstrateda relationship between maximal soil temperature at which speciesare active and recruitment behavior (which is hypothesized to be related to the presence or absence of chemical signals).The species that were active at lower temperatures proved tobe those that used chemical signals to recruit nest mates duringforaging. This is also the case when comparing sympatric speciesand thereby controlling for other environmental factors. Moreover,all seven nonrecruiter species developed from recruiter ancestries,which is consistent with our hypothesis because ample evidence suggests a forest and tropical origin for ants. Thus, contraryto previous hypotheses, species that forage individually cannotbe categorically considered primitive, but rather appear tobe derived from recruiter species. Therefore, we conclude thattemperature influences the evolution and/or stability of chemicalsignals in ants by determining the recruitment of nest mates.     

Information transfer about roosts in female Bechstein's bats: an experimental field study

Information transfer among group members is believed to play an important part in the evolution of coloniality in both birds and bats. Although information transfer has received much scientific interest, field studies using experiments to test the underlying hypotheses are rare. We used a field experiment to test if communally breeding female Bechstein's bats (Myotis bechsteinii) exchange information regarding novel roosts. We supplied a wild colony, comprising 17 adult females of known relatedness, with pairs of suitable and unsuitable roosts and monitored the arrival of individuals marked with transponders (PIT-tags) over 2 years. As expected with information transfer, significantly more naive females were recruited towards suitable than towards unsuitable roosts. We conclude that information transfer about roosts has two functions: (i) it generates communal knowledge of a large set of roosts; and (ii) it aids avoidance of colony fission during roost switching. Both functions seem important in Bechstein's bats, in which colonies depend on many day roosts and where colony members live together for many years.     

Selection on body size in a raptor with pronounced reversed sexual size dimorphism: are bigger females better?

An overabundance of hypotheses have been proposed to accountfor reversed sexual size dimorphism (RSD; females the largersex) in raptors. Previous research principally focused on examininginterspecific patterns of RSD, rarely testing predictions ofvarious hypotheses within populations. To redress this, we useddata from both sexes of a large brown falcon, Falco berigora,population to evaluate the importance of size and body conditionindices on the hunting prowess of males and the reproductivesuccess, recruitment, and survival probabilities of both sexes.Female-female competition for territorial vacancies was likelyto be intense as the floating population was female-biased andintrasexual agonistic interactions were frequently observed.In this competitive population, larger adult females were morelikely to be recruited, indicating directional selection favoringincreased female body size. Furthermore, after recruitment largerfemales were more likely to successfully fledge offspring, providinga mechanism by which RSD is maintained in the population. Incontrast, male recruitment was unrelated to either body sizeor condition indices. Smaller immature males more often heldtheir territories (survived) over two breeding seasons thandid their larger counterparts; however, they also took smallprey more frequently, a diet related to poor reproductive success.We argue that, together, these results are indicative of selectionfavoring an increase in female body size and a reduction ormaintenance in male body size. Of all the hypotheses proposedto account for the maintenance and evolution of RSD in raptors,this scenario is consistent only with the predictions of theintrasexual competition hypothesis.     

Recruitment, Search Behavior, and Flight Ranges of Honey Bees

During the past three decades, considerable evidence has beengathered in attempts to understand more fully honey bee recruitmentto food sources. Those efforts also apply directly to two long-standingand competing recruitment hypotheses: odor search vs. "dancelanguage" communication. However, whereas most researchers havefocused on individual interactions and behavior, the colonycan also be viewed as a unit. A review of evidence from a colonyperspective reveals that colony members range an average distancefrom their home base, whether while foraging on food sources,while collecting water, or while relocating as swarms. Thoseaverages, based on the logarithm of the distance from the colony,vary with the type of resource exploited and size of the odorfield. Such a mathematical correspondence between distancestravelled from parent colonies may well agree with an odorsearchrecruitment model, but is hardly reconcilable with the "dancelanguage" hypothesis.     

Genetic similarity in long-eared owl communal winter roosts: a DNA fingerprinting study

The long-eared owl is a nocturnal predator which winters communally and breeds in the same areas in loose colonies during the spring. We tested the hypothesis that roosts, particularly stable roosts, are formed by close relatives, a condition under which group-related behaviours such as information sharing or helping at nest are more likely to be developed. DNA fingerprinting analysis was used to examine genetic similarity within and between two long-eared owl populations, one wintering in a traditional roost and the other in an unstable roost, and both breeding around their roosting sites. Although genetic similarity within roosts was higher than that between roosts, the difference was not significant. Observed genetic similarity within roosts was smaller than that reported in the bird species whose roosts work as information centres. On the other hand, the presence of some closely related individuals in the roost and behavioural observations suggest that co-operation between kin might have occurred, at least in one of the two study sites.     

Hydrocarbons Emitted by Waggle-Dancing Honey Bees Increase Forager Recruitment by Stimulating Dancing

Hydrocarbons emitted by waggle-dancing honey bees are known to reactivate experienced foragers to visit known food sources. This study investigates whether these hydrocarbons also increase waggle-dance recruitment by observing recruitment and dancing behavior when the dance compounds are introduced into the hive. If the hydrocarbons emitted by waggle-dancing bees affect the recruitment of foragers to a food source, then the number of recruits arriving at a food source should be greater after introduction of dance compounds versus a pure-solvent control. This prediction was supported by the results of experiments in which recruits were captured at a feeder following introduction of dance-compounds into a hive. This study also tested two nonexclusive behavioral mechanism(s) by which the compounds might stimulate recruitment; 1) increased recruitment could occur by means of increasing the recruitment effectiveness of each dance and/or 2) increased recruitment could occur by increasing the intensity of waggle-dancing. These hypotheses were tested by examining video records of the dancing and recruitment behavior of individually marked bees following dance-compound introduction. Comparisons of numbers of dance followers and numbers of recruits per dance and waggle run showed no significant differences between dance-compound and solvent-control introduction, thus providing no support for the first hypothesis. Comparison of the number of waggle-dance bouts and the number of waggle runs revealed significantly more dancing during morning dance-compound introduction than morning solvent-control introduction, supporting the second hypothesis. These results suggest that the waggle-dance hydrocarbons play an important role in honey bee foraging recruitment by stimulating foragers to perform waggle dances following periods of inactivity.     

Summer tree roost selection by Rafinesque's big-eared bat

Roost requirements of most North American forest bats are well-documented, but questions remain regarding the ultimate mechanisms underlying roost selection. Hypotheses regarding roost selection include provision of a stable microclimate, space for large colonies, protection from predators, and proximity to foraging habitat, among others. Although several hypotheses have been proposed, specific mechanisms likely vary by species and geographic region. Rafinesque's big-eared bat (Corynorhinus rafinesquii) commonly roosts in trees with large basal hollows in the Coastal Plain of the southeastern United States. Our objective was to weigh evidence for hypotheses regarding selection of diurnal summer roosts by Rafinesque's big-eared bat at 8 study sites across the Coastal Plain of Georgia, USA. We used transect searches and radiotelemetry to locate roosts and measured 22 characteristics of trees, tree cavities, and surrounding vegetation at all occupied roosts and for randomly selected unoccupied trees. We evaluated 10 hypotheses using single-season occupancy models and used Akaike's information criterion to select the most parsimonious models. We located 170 tree roosts containing approximately 870 bats for our analysis. The best supported model predicted bat presence from cavity size, interior wall texture, and number of entrances. Because large cavities allow bats to fly and smooth walls impede attacks by terrestrial predators, our results are consistent with the hypothesis that bats select roosts that allow them to evade predators. However, data on predation rates are needed for a conclusive determination. Because trees suitable as roosts for Rafinesque's big-eared bat are rare in the landscape, protection of suitable forested wetland habitat is essential to provide current and long-term roost tree availability. © 2012 The Wildlife Society.     

灵长类动物的食物分享行为

食物分享是灵长类动物的一种重要社会交往行为,主要发生在成体-幼体间和成体-成体之间。本文从这两个方面对灵长类动物食物分享的行为表现、特点以及功能进行总结,着重比较了无亲缘关系的成年个体间食物分享的互惠解释和骚扰解释。通过对以上内容的综合分析,进一步提出了食物分享行为的未来研究方向以及对人类合作行为演化的启示。     

Public information and conspecific nest parasitism in goldeneyes: targeting safe nests by parasites

Conspecific nest parasitism (CNP) is a widespread alternativereproductive tactic in birds. Several hypotheses have been putforward to explain the evolution and occurrence of CNP, butno generally applicable hypothesis exists. Recent experimentalresults from the common goldeneye (Bucephala clangula), a cavity-nestingduck, have revealed that parasitic females preferentially layeggs in safe nest-sites, implying that nest predation risk isan important ecological determinant of CNP. The present studyfocuses on the mechanisms by which parasites identify safe nest-sites.Predation risk of a given nest-site was predictable betweensuccessive breeding seasons. At the end of the nesting season,females prospected active nest-sites more frequently than nest-sitesthat did not have a nest in the current season. Nest-sites thathad been prospected more frequently by females in year t hada higher probability to be parasitized in year t + 1. The resultssuggest that the use of public information, derived throughnest-site prospecting, enabled parasites to target safe nests.These findings provide a new and potentially generally applicableperspective to understand the evolution and occurrence of CNP.     

High fidelity: extra‐pair fertilisations in eight Charadrius plover species are not associated with parental relatedness or social mating system

Extra‐pair paternity is a common reproductive strategy in many bird species. However, it remains unclear why extra‐pair paternity occurs and why it varies among species and populations. Plovers (Charadrius spp.) exhibit considerable variation in reproductive behaviour and ecology, making them excellent models to investigate the evolution of social and genetic mating systems. We investigated inter‐ and intra‐specific patterns of extra‐pair parentage and evaluated three major hypotheses explaining extra‐pair paternity using a comparative approach based on the microsatellite genotypes of 2049 individuals from 510 plover families sampled from twelve populations that constituted eight species. Extra‐pair paternity rates were very low (0 to 4.1% of chicks per population). No evidence was found in support of the sexual conflict or genetic compatibility hypotheses, and there was no seasonal pattern of extra‐pair paternity (EPP). The low prevalence of EPP is consistent with a number of alternative hypotheses, including the parental investment hypothesis, which suggests that high contribution to care by males restricts female plovers from engaging in extra‐pair copulations. Further studies are needed to critically test the importance of this hypothesis for mate choice in plovers.     

The diversity and evolution of recruitment behaviour in ants,with a discussion of the usefulness of parsimony criteria in the reconstruction of evolutionary histories

Summary Three alternative hypotheses about the evolution of recruitment behaviour in ants, based on accounts in the literature, are compared by means of a cladistic analysis. The three hypotheses are the following:Hypothesis 1. Increasingly efficient recruitment behaviours exhibited by different ant species have been shaped by or are correlated with ant phylogeny.Hypothesis 2. Increasingly efficient recruitment behaviours represent necessary evolutionary steps independently followed during the evolution of different ant clades.Hypothesis 3. Differently efficient recruitment behaviours have been selected in a convergent way among different species by similar population/environmental constraints.In a first stage of the analysis, these hypotheses have been compared in terms of parsimony (i.e. in terms of tree length = TL) of alternative cladograms based on recruitment behaviour only. The analysis gave the following results: Hypothesis 1, TL = 4; Hypothesis 2, TL = 18; Hypothesis 3, TL = 11. At least in terms of parsimony, hence, Hypothesis 1 appears to be the best. This hypothesis, however, cannot be retained for its total lack of congruence with current views on ant phylogeny. Among the remaining two hypotheses, Hypothesis 3 is again much (ca. 40%) more parsimonious than Hypothesis 2, but the retention index for recruitment behaviour on the relative cladogram is 0.2 as compared with 0.7 for Hypothesis 2. Practically, this implies biologically very implausible behavioural evolution indicated by very improbable ancestors for the species included in the analysis. In the case of recruitment evolution the biological credibility of each hypothesis is inversely proportional to its parsimony.The three hypotheses on the evolution of recruitment behaviour are compared again taking into account the morphological and behavioural correlates of recruitment. The results confirm those obtained by simple cladistic analysis of behaviour alone, namely that an obligatory (i. e. neither reversible nor random) increase in recruitment efficiency has been repeatedly selected within different ant clades. Inclusion of the recruitment correlates allows, in addition, a more precise formulation of the implications of each hypothesis and a tentative test of two other alternatives deduced from the literature. Most papers dealing with recruitment assume this behaviour to be controlled by a single gland, while at least two experimental analyses show that more than one gland is likely to be involved as behavioural releaser. A cladistic approach allowed testing of the following two adaptational hypotheses: A) Synergic behavioural control by several glands, allowing shift of the dominant role from one gland to another. B) Single gland control, making improbable the replacement of one gland by another that performs the same function. The results of the analysis appear to favour alternative A slightly, though neither alternative results in implausible evolutionary paths.It is stressed that parsimony remains the sole decisional criterion when no other criteria are available but it can by no way be preferred to the slightest trace of biological common sense.     

Host group formation decreases exposure to vector-borne disease: a field experiment in a ‘hotspot’ of West Nile virus transmission

Animals can decrease their individual risk of predation by forming groups. The encounter-dilution hypothesis extends the potential benefits of gregariousness to biting insects and vector-borne disease by predicting that the per capita number of insect bites should decrease within larger host groups. Although vector-borne diseases are common and can exert strong selective pressures on hosts, there have been few tests of the encounter-dilution effect in natural systems. We conducted an experimental test of the encounter-dilution hypothesis using the American robin (Turdus migratorius), a common host species for the West Nile virus (WNV), a mosquito-borne pathogen. By using sentinel hosts (house sparrows, Passer domesticus) caged in naturally occurring communal roosts in the suburbs of Chicago, we assessed sentinel host risk of WNV exposure inside and outside of roosts. We also estimated per capita host exposure to infected vectors inside roosts and outside of roosts. Sentinel birds caged inside roosts seroconverted to WNV more slowly than those outside of roosts, suggesting that social groups decrease per capita exposure to infected mosquitoes. These results therefore support the encounter-dilution hypothesis in a vector-borne disease system. Our results suggest that disease-related selective pressures on sociality may depend on the mode of disease transmission.     

Management of fat reserves and food caches in tufted titmice (Parus bicolor) in relation to unpredictable food supply

In the temperate zone, permanent-resident birds and mammalsthat do not hibernate must survive harsh winter conditions oflow ambient temperature, long nights, and reduced food levels.To understand the energy management strategy of food-hoardingbirds, it has been hypothesized that such birds respond to increasedstarvation risk by increasing the number of their hoards ratherthan by increasing their fat reserves and that they cache earlyin the day and retrieve their caches later to achieve fat reservesnecessary to survive the night We tested these hypotheses byobserving the responses in captivity of a caching bird, thetufted titmouse (Parus bicolor), to the combined influencesof reduced predictability of food and naturally occurring ambienttemperature and photoperiod. When the food supply was unpredictable,birds significantly increased both internal fat reserves atdusk and external food caches. Initially leaner birds tendedto increase their fat reserves to a greater extent and initiallyfatter birds tended to cache more food and to fly significantlyless. Half the birds also increased their dawn and mean dailybody mass. All birds tended to forage, gain body mass, and cachefood at significantly lower rates in the morning and at significantlyhigher rates in the evening. Cache retrieval showed the oppositetrend, with birds retrieving most of their caches in the morning.Our results do not support the hypothesis that caching birdsincrease caching rate but not body mass under an unpredictablefood regime. Instead fat reserves and food caches are both importantcomplementary sources of energy in food-hoarding birds. Energymanagement by wintering birds occurs in response to a numberof biotic and abiotic factors acting simultaneously; thus futuremodels must incorporate independent variables in addition tothe state of the food supply and time of day     

Why female crested tits copulate repeatedly with the same partner: evidence for the mate assessment hypothesis

That repeated copulation with the same partner within a singlefertile period is beneficial to the male is generally accepted,but why it should be adaptive to the female is controversialand clear evidence supporting any hypothesis is lacking. Hunteret al. (1993) presented seven hypotheses explaining repeatedmating from the female perspective. Four of them are consistentwith the occurrence of male refusal to copulate: females mighttrade copulations for (1) immediate and or (2) future materialbenefits, or use mating as a mechanism for (3) mate-guardingand or (4) mate-assessment. To test these hypotheses in a populationof crested tits Parus cristatus, we collected data on variationin female solicitation rate, proportion of male refusal, andextra-pair paternity. We found that (1) female solicitationrate was independent of male condition, (2) the proportion ofmale refusal was higher in poor-condition males and (3) femalespaired to poor-condition males sought extra pair paternity.These findings agree with predictions stemming from the mateassessment hypothesis. Therefore, it is suggested that, in crestedtits, male response to female copulation solicitation reflectsmale condition and is used by females to assess male quality