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Food-sharing signals among socially foraging Cliff Swallows

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Abstract

Colonially nesting cliff swallows, Hirundo pyrrhonota, in southwestern Nebraska use a vocal signal, termed the squeak call, which alerts conspecifics that food has been found. Birds were recruited to playbacks of this call, and the frequency of calling increased when insect swarms were provided to the swallows. Squeak calls were used mostly while birds were foraging in loose groups away from their colonies. Calling occurred primarily on days when temperatures were less than 17°C, solar radiation was less than 500 W/m2, and wind speed was less than 26 km/h, conditions under which foraging success was presumably poor. Weather conditions appropriate for calling occurred regularly, with an average 24·5% of days in each breeding season suitable for use of the squeak call. Calling probably improves the caller's own foraging efficiency. By recruiting other foragers to a discovered food source, the caller may increase the chances that the insects' movements will be tracked and thus that the caller itself will be able to exploit the insect swarm for a longer time.
... First, social predators can have a better chance of discovering prey (Giraldeau & Caraco, 2018). Predators in groups have access to a pool of social information from other members, which can be transferred through cues -like the sounds a bat makes when catching prey (Dechmann et al., 2009), or by signals -like the vocalisations swallows use to recruit conspecifics (Brown, Brown, & Shaffer, 1991). Second, group hunting can enhance prey capture (Beauchamp, 2013), enabling predators to corral, confuse and dismantle prey collectives (Handegard et al., 2012), or cooperatively subdue large, dangerous prey (Stander, 1992). ...
... Predators use active signals to recruit or synchronise others at discovered food resources. Recruitment of group members can enhance prey capture success and individual foraging efficiency (Brown et al., 1991), or for mesopredators recruiting larger groups can help reduce individual vigilance for superpredators (Lima & Dill, 1990). The active signalling of food discovery can be via different modalities, but is most frequently communicated using vocalisations (Clay, Smith, & Blumstein, 2012). ...
... The active signalling of food discovery can be via different modalities, but is most frequently communicated using vocalisations (Clay, Smith, & Blumstein, 2012). For example, cliff swallows (Hirundo pyrrhonota) that find insect swarms use vocal 'squeak calls' to signal conspecifics to feed (Brown et al., 1991). Communication at discovered prey also appears to function as a means to synchronise prey capture in certain groups of predators, such as packs of dhole (Cuon alpinus) (Fox, 1984) and schools of mormyrid fish (Mormyrops anguilloides) (Arnegard & Carlson, 2005). ...
... These information-sharing properties have led some researchers to label food-associated calls as 'functionally referential signals' (Evans and Evans 1999;Kitzmann and Caine 2009;Slocombe and Zuberbühler 2005) and look toward this calling behavior for insights into the evolutionary origins of human language (Fedurek and Slocombe 2011;Zuberbühler 2003). Nevertheless, food-associated calls represent an evolutionary puzzle since drawing attention to discovered food may attract other foragers to the feeding site (Brown et al. 1991;Chapman and Lefebvre 1990;Elgar 1986a;Heinrich 1988;Laidre 2006). Such behavior has the potential to reduce the signaler's food intake (Di Bitetti and Janson 2001;Hake and Ekman 1988;Laidre 2006) and thereby negatively affect the signaler's reproductive success. ...
... Most research exploring the function of food-associated calling behavior has focused on its ability to inform others of discovered food and/or attract them to the food source. Studies indicate that the food-associated calls of some species can promote food-seeking behavior in receivers Evans 1999 2007), increase the likelihood that others approach the discovered food (Chapman and Lefebvre 1990;Elgar 1986a;Heinrich 1988), reduce the amount of time it takes for others to arrive at the food patch (Chapman and Lefebvre 1990;Elgar 1986a), or increase the total number of individuals that arrive (Brown et al. 1991;Laidre 2006). Signalers may benefit from this increase in foraging group size through a reduction in predation risk or vigilance levels (Chapman and Lefebvre 1990;Elgar 1986b), an increase in mating opportunities (Evans and Marler 1994) or an increase in the signaler's ability to defend the discovered food (Heinrich 1988). ...
Article
Food-associated calls have received much research attention due to their potential to refer to discovered food in a word-like manner. Studies have found that in many species, food-associated calls attract receivers to the food patch, suggesting these calls play roles in food sharing, cooperation and competition. Additionally, in various species, these calls play a role that has received much less attention: mediating social interactions among foragers that are already nearby or within the food patch, independently of whether they attract outside foragers. In order to increase understanding of the function of the chimpanzee (Pan troglodytes) food-associated rough grunt, we conducted captive playback studies testing whether rough grunt playbacks attract, repel or have no effect on the proximity of foragers already familiarized with the presence of food. We tested how acoustic playbacks of rough grunts (or control calls) from one of two known, identical feeding sites affected receivers’ approach and feeding behaviors. More often than expected, participants first approached the feeding site from which rough grunts, but not control calls, were broadcast. However, neither condition increased the likelihood that participants fed first from a given site. Our results support the hypothesis that rough grunts elicit an approach response in receivers, while providing no evidence that they repel. In addition, our study provides evidence that receivers may approach rough grunts even if they do not intend to feed. We discuss the information rough grunts may convey to receivers beyond information about discovered food and the potential benefits signalers may gain from this calling behavior.
... A parallel case is food sharing in social cliff swallows, which alert conspecifics when insect swarms are found. Efficient group tracking of swarms can benefit the caller through increased foraging (Brown et al. 1991). ...
... Many vertebrate taxa communicate using acoustic signals including mammals, birds, amphibians and fish (Fitch & Suthers, 2016). Communication and signalling can increase fitness in myriad contexts, including sexual selection (G emard et al., 2021), predator avoidance (Newar & Bowman, 2020), parental care (Boucaud et al., 2017) and cooperative behaviour that promotes energetic gain (Brown et al., 1991) or decreases energetic loss (Sagot et al., 2018). Although most examples arise from model systems, there is increasing interest in leveraging nonmodel systems to diversify our understanding of signalling evolution and behaviour (Doody et al., 2013). ...
Article
Signals are fundamental to communication, and theory suggests signals may evolve to coordinate cooperation on complex tasks. Several recent studies have demonstrated that hatchling turtles vocalize within the subterranean nest cavity, and these vocalizations are hypothesized to promote hatching synchrony and coordinate emergence from subterranean nests (social facilitation hypothesis). Here we test assumptions and predictions of the social facilitation hypothesis in the snapping turtle, Chelydra serpentina, a species with a broad distribution. First, we demonstrate that C. serpentina hatchlings have a vocal repertoire: we identified six types of vocalizations in a simulated nest environment, with one vocalization type occurring before egg pipping and all six types occurring in the 24 h following egg pipping and hatching. We found that Simpson's diversity was greater for vocalizations during the hatching stage compared to the emergence stage and was minimal during the prepipping stage. Second, we manipulated egg burial depth (shallow or deep) and sociality (presence or absence of siblings) in a 2 × 2 factorial design. We found that eggs in the social treatment hatched earlier and lost less mass while emerging from the nest, underlining a likely energetic benefit to hatchlings emerging with siblings versus emerging alone. Third, we tested a subhypothesis of the social facilitation hypothesis, which is that embryos cue hatching in response to hatchling vocalizations. However, vocalization playback to late-stage (prepipping) embryos did not alter pipping date relative to controls. Our combined results provide some support for the social facilitation hypothesis: there are likely energetic benefits to group emergence, embryos in a group hatch earlier, but earlier group hatching is not cued by vocalizations per se. Our study contributes to a growing literature on the adaptive significance of sociality in reptiles and helps disentangle the proximate drivers of vocalizations in hatchling turtles.
... Acoustic signals produced only in specific contexts become linked to a specific signal function and thus can provide information about their general environment. For example, the presence of predators can be advertised through alarm calls (Seyfarth et al. 1980;Blumstein and Armitage 1997a;Macedonia and Evans 2010;Moran 2010), detection of food through species-specific foraging calls (Chapman and Lefebvre 1990;Brown et al. 1991;Hauser et al. 1993;Mahurin and Freeberg 2009), and the emitter's social intentions through aggression or courtship calls (Owen et al. 2006;Charlton et al. 2007;Ballentine et al. 2008;Faragó et al. 2010). On a secondary level, vocalizations from the species vocal repertoire convey both static and dynamic information on the emitter . ...
Article
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The cape fur seal is one of the most colonial mammal species in the world. Breeding colonies are composed of harems held by mature males (older than 10 years) with up to 30 females and their pups, while roaming subadult males (younger and socially immature) are kept away from bulls’ territories. As in other pinnipeds, cape fur seals are highly vocal and use acoustic signals in all their social interactions. Males produce barks—short vocalizations always produced in sequences—for territorial defense, mating behaviors, and agonistic interactions. These calls convey information about the sex, age class, and individual identity. This study investigated whether motivational cues such as the arousal state can be encoded in territorial males’ barks and whether these cues are decoded by listening sub-adult males. The rate (number of calls per unit of time) and fundamental frequency of barks were found to significantly increase during high arousal state interactions (i.e., male-male confrontation) compared to spontaneous barks. Playback experiments revealed that subadult males responded with a higher level of vigilance when territorial males’ barks had a faster bark rate. This mechanism of decoding the bulls’ arousal state from barks will likely constitute an advantage for both bulls and the subadult males, by avoiding or reducing physical conflicts, and thereby reducing energy expenditure and the risk of injury. This study is the first experimental evidence of cape fur seals’ using vocal rhythmic patterns to modulate their social interactions.
... In variable and unpredictable habitats, animals may benefit from altering their foraging behaviour based on the behaviour of other individuals, as such social influence may allow them to reduce the uncertainty about the consequences of their foraging decisions (Bonnie & Earley, 2007;Boyd et al., 2016;Valone & Templeton, 2002). For instance, cliff swallows, Petrochelidon pyrrhonota, searching for food are recruited by the squeak calls of other swallows that have already found prey (Brown et al., 1991). Conversely, animals may also indicate poor feeding conditions through their vocalizations, for instance through a change in their production rate as observed in passerine birds (Berget et al., 2005;Lucas et al., 1999). ...
Article
In many bird species, reproductive partners sing together each time they meet on the nest. Because these nest ceremonies typically correspond to the return of one partner from foraging and to the subsequent departure of the other partner, we hypothesized that the foraging decisions of departing birds may be facilitated by the vocalizations accompanying their partner's return on the nest, providing these vocalizations reflect foraging conditions. We examined this hypothesis in pairs of Adélie penguins, Pygoscelis adeliae, by longitudinally monitoring their nest vocalizations and their spatial distribution when foraging at sea across the guard stage, when both parents regularly alternate foraging at sea and chick attendance at the nest. We found that the acoustic characteristics of the vocalizations produced during nest relief ceremonies reflected some characteristics of the foraging trips of both the returning and departing partners. However, these acoustic characteristics differed between partners and were differently related to their foraging behaviour. Accordingly, departing individuals did not adopt the same foraging behaviour as that of returning individuals. Nest vocalizations therefore do not appear to represent cues facilitating the foraging decisions of departing birds, but they may rather reflect the arousal of partners, which differently correlates with the foraging behaviour of the returning and departing individuals. Our study highlights an interplay between the vocalizations produced on the nest by reproductive partners and their foraging behaviour, thereby broadening the scope of animal vocalizations and opening a novel perspective on the regulation of foraging strategies. However, our exploratory study also highlights the complexity of examining this interplay, as the effects of nest vocalizations on foraging decisions may be complicated by other factors (e.g. intrinsic foraging capacity). This calls for the use of additional and experimental approaches (e.g. vocalization playbacks) to clarify the role of nest vocalizations as potential mediators of foraging decisions.
... With the exception of a single report of fin whales feeding at the surface in perfect synchrony [75], there is no evidence of cooperative feeding in fin whales. Nevertheless, attracting other whales to the foraging site may increase the chances of tracking prey movements, thus prolonging feeding opportunities for callers, as suggested for cliff swallows (Petrochelidon pyrrhonota) feeding on insect swarms [76]. Fin whales often occur in temporary foraging aggregations in our study area and elsewhere [26,47]. ...
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Animals use varied acoustic signals that play critical roles in their lives. Understanding the function of these signals may inform about key life history processes relevant for conservation. In the case of fin whales (Balaenoptera physalus), that produce different call types associated with different behaviours, several hypotheses have emerged regarding call function, but the topic still remains in its infancy. Here, we investigate the potential function of two fin whale vocalizations, the song-forming 20-Hz call and the 40-Hz call, by examining their production in relation to season, year and prey biomass. Our results showed that the production of 20-Hz calls was strongly influenced by season, with a clear peak during the breeding months, and secondarily by year, likely due to changes in whale abundance. These results support the reproductive function of the 20-Hz song used as an acoustic display. Conversely, season and year had no effect on variation in 40-Hz calling rates, but prey biomass did. This is the first study linking 40-Hz call activity to prey biomass, supporting the previously suggested food-associated function of this call. Understanding the functions of animal signals can help identifying functional habitats and predict the negative effects of human activities with important implications for conservation.
... It is important to keep in mind that the studies in Table 1 explicitly set out to examine cooperation; many studies with a different focus, but which fit under the various definitions of cooperation in Section (1) may be missing. For example, studies that consider various aspects of social tolerance, food-sharing, signalling/alarm-calling and other behaviours that are generally accepted as prosocial (defined as unsolicited acts of help or assistance to others) can give us insights into the way cooperation spreads or is maintained in natural populations (Brown, Brown & Shaffer, 1991;Jaeggi, Burkart & Van Schaik, 2010;Jaeggi & Gurven, 2013;Bonadonna et al., 2020). There may be other systems which are well suited for the study of cooperation that have not previously been directly framed in this context. ...
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Understanding why individuals carry out behaviours that benefit others, especially genetically unrelated others, has been a major undertaking in many fields and particularly in biology. Here, we focus on the cooperation literature from natural populations and present the benefits of a social network approach in terms of how it can help to identify and understand factors that influence the maintenance and spread of cooperation, but are not easily captured when solely considering independent dyadic interactions. We describe how various routes to cooperation can be tested within the social network framework. Applying the social network approach to data from natural populations can help to uncover the evolutionary and ecological pressures that lead to differences in cooperation and other social processes.
... A single bird flies over an area in search of food, a tiger roams the jungle, or a person scans their terrain for resources. Other times, foraging is studied as a collective activity that groups of organisms engage in [1][2][3][4] . Collective foraging occurs when groups of organisms interact and move together while searching for resources, and it is more often associated with organisms that have limited cognitive capacities for planning and decision-making. ...
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Colonically nesting cliff swallows, Hirundo pyrrhonota, in southwestern Nebraska, U.S.A., often forage socially, in groups of two to more than 1000 individuals, on ephemeral concentrations of insects. Social foraging was promoted through information transfer among individuals at fixed colony sites, and through local enhancement in which foraging activities of some individuals attracted others to a food source. Cliff swallows feeding in groups had greater average foraging success (prey capture attempts per min) than birds feeding solitarily. Variance in prey capture success, and thus foraging risk, declined with group size and was greatest for solitary foragers. Solitary cliff swallows whose foraging success equalled or exceeded that expected from social foraging remained solitary during a given foraging bout. Solitary foragers whose success fell below that expected from social foraging joined foraging groups. For individuals foraging socially there was no consistent relationship between foraging success and group size, indicating little competition among group members for food and little resource depression. Social foraging in cliff swallows is probably not an adaptation mainly to decrease individuals' risk of predation because foraging success did not differ for birds foraging on the edges versus in the centres of groups, and individuals foraging on the edges did not try to move toward the centre. These data are consistent with risk-sensitive foraging models and provide the first empirical demonstration with free-living animals that social foraging is associated with decreased individual variance in foraging success.
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