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Cooperative bird discriminates between individuals based purely on their aerial alarm calls

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Abstract

From an evolutionary perspective, the ability to recognize individuals provides great selective advantages, such as avoiding inbreeding depression during breeding. Whilst the capacity to recognize individuals for these types of benefits is well established in social contexts, why this recognition might arise in a potentially deadly alarm-calling context following predator encounters is less obvious. For example, in most avian systems, alarm signals directed toward aerial predators represent higher predation risk and vulnerability than when individuals vocalize toward a terrestrial-based predator. Although selection should favor simple, more effective alarm calls to these dangerous aerial predators, the potential of these signals to nonetheless encode additional information such as caller identity has not received a great deal of attention. We tested for individual discrimination capacity in the aerial alarm vocalizations of the noisy miner (Manorina melanocephala), a highly social honeyeater that has been previously shown to be able to discriminate between the terrestrial alarm signals of individuals. Utilizing habituation–discrimination paradigm testing, we found conclusive evidence of individual discrimination in the aerial alarm calls of noisy miners, which was surprisingly of similar efficiency to their ability to discriminate between less urgent terrestrial alarm signals. Although the mechanism(s) driving this behavior is currently unclear, it most likely occurs as a result of selection favoring individualism among other social calls in the repertoire of this cooperative species. This raises the intriguing possibility that individualistic signatures in vocalizations of social animals might be more widespread than currently appreciated, opening new areas of bioacoustics research.

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... This study was conducted on a wild population of noisy miners at Newholme Field Research Station (30°25ʹS, 151°38ʹE), a rural property approximately 7 km northwest of Armidale managed by the University of New England, chosen as it supports a high density of noisy miners. This colony of ~ 100 adults inhabits a patch of remnant eucalypt woodland (~ 75 ha) in a heavily-cleared agricultural landscape, and has been studied since 2011 (Barati et al. 2016, 2018, Farrow et al. 2020. We elected to run playback experiments on a single colony, as whether there is geographic variation in the mobbing behaviour of the species is currently unknown. ...
... Our work suggests that these acoustic differences are meaningful, and that noisy miners use them to discriminate between familiar and unfamiliar conspecifics. While past work using both chur calls and aerial alarm calls has demonstrated this ability in a captive setting (McDonald 2012, Farrow et al. 2020, this is the first time it has been shown in the wild. Noisy miners may respond more quickly to unfamiliar individuals outside the colony if they view them as a threat (Blackburn et al. 2023). ...
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Mobbing is a widespread, vocally coordinated behaviour where species approach and harass a threat. The noisy miner (Manorina melanocephala) is a notorious native Australian honeyeater, well‐known for its hyperaggressive mobbing. Numerous studies have identified negative impacts of their mobbing behaviour, highlighting the exclusion of competitors from colony areas and the resulting loss of woodland‐bird biodiversity. Despite this, few studies have investigated mobbing itself, and our understanding of the factors which influence its expression remains limited. Here, we use a field‐based playback experiment to investigate whether mobbing responses vary in relation to colony borders and caller familiarity. Noisy miners were more likely to respond, reacted more quickly and responded more strongly to mobbing calls broadcast inside as opposed to outside the colony. These behavioural differences likely arise from variation in the relative costs and benefits of responding. When noisy miners did mob outside the colony, more individuals joined in response to unfamiliar as opposed to familiar callers. Our results reveal that noisy miner mobbing may not be as indiscriminate as often assumed, with caller familiarity and location influencing this behaviour. We suggest there are benefits to greater consideration of the factors impacting noisy miner mobbing behaviour. Keywords: Avian biodiversity, interspecific aggression, mobbing behaviour, noisy miner, vocal communication
... Playback procedure Calls used during the playback procedure were obtained by Farrow et. (2020) with all call exemplars used being unfamiliar (temporally separated) to subjects in order to avoid past experience impacting responses. Vocalisations from signallers used in experiments were recorded from colonies located at Dumaresq Dam (30°30'S, 151°40'E) and the University of New England Newholme Field Research Station (30°25'24''S; ...
... Due to the di culty of determining gaze direction, we used the method deployed in past experiments that investigated differentiation of signallers (McDonald 2012; Farrow et al. 2017;Farrow et al. 2020) to measure the most informative responses in playbacks to this species, which were: 1) initial time to rst respond (a head turn > 5 ° without the body moving) to the signal (measured in 24 frames per second), 2) degree to which the head moved in response to the signal and 3) duration of this initial head turn (fps). Degree of head turn was measured by Pixel Stick version 2.16.2 (Plum Amazing Software LLC). ...
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True individual recognition refers to an animal's ability to recognise at least one unique feature of another individual. Demonstrating this in animals equivocally can be difficult, as it requires confounding variables such as location, kinship or familiarity to be carefully controlled. This is problematic, as a poor understanding of how individual recognition operates limits our understanding of pathways that shape intelligence, sociality, and cooperation in taxa. Noisy miners ( Manorina melanocephala ) are a highly social bird that exhibits multiple cooperative behaviours accompanied by functionally referential vocal signals, providing an ideal model for studying recognition. We employed an adapted habituation-discrimination paradigm to experimentally demonstrate true individual recognition in miners, as a receiver’s habituation to a calling individual transferred across different social contexts. This was observed in wild birds that were not subject to any additional training, and exhibited even by receivers exposed to novel signallers. These findings have significant implications for understanding the mechanisms underlying avian cooperation and cognition in complex animal societies, and indicate that recognition in this species is likely based on individual vocal characteristics.
... There is a possibility that the miners studied may have reduced their aggression during the trial in response to the presence of a human following shooting, and that aggression towards live birds remained unchanged outside of the experiment. Miners that heard playback during presentations may also have learned to associate our broadcast stimuli with danger, as the species possesses excellent vocal recognition (McDonald 2012;Farrow et al. 2019). We reduced the latter risk by randomising call playback during trials, however the importance of a human's impact on mobbing intensity post-culling is currently unknown and a potential focus of future research in this space. ...
... An alternative approach, a habituationdishabituation (H-D) test, may offer a more rapid and straightforward way of determining dogs' ODT for different odorants than other methods. This paradigm has been used across different sensory stimuli, including visual, auditory, tactile, and chemical, and with various species, including humans, other mammals, birds, fish, and insects (e.g., Farrow et al., 2020;Hostachy et al., 2019;Lejeune et al., 2021;Messina et al., 2020;Rørvang et al., 2017). It is based on the notion that animals tend to ignore familiar, irrelevant stimuli and show more interest in novel stimuli (Groves & Thompson, 1970;Pavlov, 1927;Rankin et al., 2009). ...
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The habituation–dishabituation (H–D) paradigm is an established measure of sensory perception in animals. However, it has rarely been applied to canine olfaction. It proposes that animals will lose interest in, or habituate to, a stimulus after successive exposures but will regain interest in, or dishabituate to, a novel stimulus if they can perceive it. This study assessed an H–D test's practicability to determine dogs' olfactory detection thresholds (ODTs) for a neutral odorant. A random selection of mixed‐breed pet dogs (n = 26) participated in two H–D tests in a repeated‐measures crossover design. They were first habituated to a carrier odor and then presented with either ascending concentrations of n‐amyl acetate in the known ODT range (experimental condition) or repeated carrier odor presentations (control condition). No single odor concentration elicited dishabituation in the majority of the dogs. However, individual dogs dishabituated at differing experimental concentrations significantly more often than in the control condition (p = .012). These findings provide some tentative support for using this method in studying canine olfaction. However, further assessment and refinement are needed before it can be a viable alternative to traditional ODT measurement.
... Furthermore, since most birds have the ability to fly and escape, threats on land are almost negligible for adult birds (De Neve et al. 2010). By contrast, aerial predators tend to pose greater threats to birds than terrestrial predators (Farrow et al. 2019) as some hawks can continue to hunt after their prey escapes (Mendelsohn and Jaksić 1989). Consequently, for small birds, a fast response to the calls of hawks or to calls similar to those of hawks can help them avoid risks in time. ...
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Imperfect Batesian mimicry is common in nature. Female common cuckoos (Cuculus canorus), for instance, seem to be imperfect mimics of hawks (Accipiter spp.) in both appearance and call. However, only few experiments have confirmed that female cuckoos can effectively mimic sparrowhawk calls. To test the effectiveness of female common cuckoos mimicking the call of hawks, we performed a playback experiment on two host bird species, namely the Oriental magpie-robin (Copsychus saularis) and white wagtail (Motacilla alba), and two potential host bird species, the crested myna (Acridotheres cristatellus) and Eurasian hoopoe (Upupa epops), during the non-breeding season in Hainan island, China. We found that while there are significant differences in the likelihood that different species respond to playback call types, they do not differ in how they respond to the different calls, and that overall, the birds are more likely to respond to female cuckoo and hawk calls than to dove or male cuckoo calls, and with no significant difference between hawk and female cuckoo. Our results show that although female common cuckoos mimic the call of sparrowhawks imperfectly, they can mislead birds into displaying anti-predatory behavior. This study provides further evidence to support the recently proposed hypothesis that hawk mimicry in female cuckoo calls can not only fool their hosts, but also the non-host species.
... Alternatively, individuality in echolocation calls might be inherent in the individuality of the vocal tracts or behavioral repertoires of individual bats and the ability to vocally discriminate between individuals might be found across all species of echolocating bats, including those that do not forage socially. Noisy miner birds produce a call in a nonsocial context, which has individual signatures and allows for individual discrimination (Farrow et al. 2020). This is consistent with an alternative hypothesis that selection for individual signatures in calls produced in social contexts may facilitate the same selection even in calls that have no social function. ...
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Where alarm signals function to warn others of the presence of threat, variation is likely to exist in the reliability of alarm signalers. Some signalers, with too low a threshold of excitation, will issue false alarms and should be ignored if potential alarm recipients are to maximize energy gains. We exposed juvenile Richardson's ground squirrels to reliable signalers, whose alarm calls were paired with the presentation of a predator model, and unreliable signalers, whose alarm calls were played when no potential predator was present. Call recipients discriminated among individual alarm callers, and reduced responsiveness to callers that had been unreliable. Thus, like primates, squirrels are capable of forming a concept of reliability by associating an individual's identity with that individual's past performance.
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In colonial birds, acoustic communication is essential for mate recognition. The South Polar skua (Catharacta maccormicki) lives in loose colonies and is highly territorial for feeding and breeding. We studied the potential of individual identity coding in the three main calls of the South Polar skua repertoire: the courtship, the contact and the alarm calls. We investigated parameters in both temporal and frequencial domains, i.e. amplitude modulation, frequency modulation and power spectrum density. For each parameter, the intra- and inter-individual variabilities were calculated. The ratio between these values represents the potential of individuality coding (PIC) of the considered feature. Low values of PICs for amplitude and frequency modulations show that both parameters may not be used for individual recognition. In contrast, high values of PIC for the power spectrum density indicate that the energy distribution among the frequency spectrum is likely to be an individual marker. PIC also varies according to the call type. Both courtship and contact calls have a higher potentiality of individual identity coding than the alarm call. The two former calls may allow individual recognition whereas the latter may not, and this last result can be extrapolated to many other species.
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Variation in the acoustic structure of alarm signals has mainly been viewed as coding information about the type of predator or the level of threat posed by the predator. Alarm signals can also convey individuality information, but whether conspecifics use this information and the function of individually distinct alarm calls remains unclear. In this study, we examined whether mobbing alarm calls of superb fairy-wrens (Malurus cyaneus) communicated information about sex, individual identity or kinship and whether this information was stable between years. We then examined the discriminative abilities of adults using playback experiments. We first used a habituation/dishabituation procedure to investigate whether adults were able to differentiate between two unfamiliar individuals. Then, we tested whether they adjusted their response based on their level of familiarity or kinship with the caller by comparing their response to mobbing alarm calls of their mate, a first order relative from the same population, an unrelated individual from the same population, or a distant bird from a different population. Superb fairy-wren mobbing alarm calls conveyed information about individuality, but not sex or kinship, and vocal individuality varied between years. Adults discriminated between two unfamiliar individuals and responded more strongly to playback of calls from their mate and kin versus individuals from another population. We discussed the conditions for discrimination based on individual characteristics rather than categories of individuals. © 2017 The Author 2017. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please e-mail: [email protected]
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Many animals use alarm calls in intraspecific communication to warn conspecifics of a predator's presence or to elicit coordinated group responses. However, alarm calls may also be aimed directly at the predator to discourage further pursuit. These ‘pursuit-deterrent’ signals are particularly important in the presence of ambush predators that rely on stealth to hunt prey. Here, we conducted playback experiments over a 16-month period on radiocollared ocelots, Leopardus pardalis, in Peru using audio stimuli of titi monkey (Callicebus toppini) and saki monkey (Pithecia rylandsi) alarm calls, with nonalarm loud calls as controls. We predicted that, if titi and saki alarm calls function as deterrent signals, then ocelots would move away from the sound source and leave the area following exposure to alarms but not following controls. We tracked ocelots via radiotelemetry for 30 min prior to and 30 min following experiments. At 15 min intervals we noted subject location, whether the cat was stationary or moving towards, away from or parallel to the playback area (calculated using a deflection angle) and distance travelled. Results showed a significantly different pattern in response movement between playback trials; ocelots moved away from the sound source in the majority of alarm trials but remained stationary/hidden or moved in a variety of directions following control trials. Ocelots also moved significantly farther following exposure to alarm trials than following exposure to controls. We conclude that ocelots can distinguish alarm calls from other loud calls and are deterred by alarm-calling monkeys. This is the first study to use playbacks on wild predators to test the pursuit-deterrent function of primate alarm calls.
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Prey species defend themselves behaviourally and morphologically, and often use varied antipredator strategies against dissimilar predator types (i.e. terrestrial versus aerial). Striped skunks, Mephitis mephitis, spray noxious secretions at predators and advertise this danger with deterrent behaviours and black-and-white aposematic coloration. Evidence suggests skunks are effective at deterring terrestrial mammalian predators but are vulnerable to aerial predators; how skunks assess the risk posed by different predator types, however, has not been examined empirically. We recorded the behavioural responses of skunks to audio playbacks of coyotes, Canis latrans, and great horned owls, Bubo virginianus (the primary terrestrial and aerial predators of skunks, respectively), and peregrine falcons, Falco peregrinus, and white noise as controls. Skunks ran away more often from vocalizations of their main predators, great horned owls and coyotes, than from diurnal falcon vocalizations or white noise recordings. Skunks also tended to run away sooner in response to owl vocalizations than falcon or coyote vocalizations. Finally, subjects tended to engage in vigilance more frequently in response to owl vocalizations than in response to coyote vocalizations, which together with other results suggest that skunks may perceive owls as more threatening relative to coyotes. This study elucidates how a well-defended mammal can determine which perceived threat is the riskiest and alter its behaviour when its main defence strategy may not be successful against all predator types.
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Alarm calls that carry information about the identity of the caller may help the receiver decide how to react. We recorded the tsik calls of six captive adult marmosets (Callithrix jacchus) in two different social groups in response to snake models at two time points (summer 2014 and January 2015). We measured eight acoustic variables including duration, inter-call interval, minimum and maximum frequency, and starting, maximum and ending peak frequency. Discriminant function analyses (DFA) confirmed that calls were individually distinct at both time periods (78.88 and 79.89% correctly classified at time one and time two, respectively). Stability of the vocal signatures was assessed using the DFA model for summer 2014 to classify calls elicited in January 2015. Although the classification rates were lower in 2015, calls were still classified more than would be expected by chance (64.50%). This suggests that acoustic signatures of common marmoset tsik calls remain fairly stable over time and therefore remain recognizable by their groupmates. However, during that six-month period, at least three (out of seven) acoustic parameters changed such that they were significantly higher or lower in all six marmosets; in two marmosets six out of seven parameters changed. Changes to individual ‘voices’ of animals, despite overall stability reflected in above-chance matching of calls over time in a DFA analysis, may have implications for acoustic research.
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Individual specificity can be found in the vocalizations of many avian and mammalian species. However, it is often difficult to determine whether these vocal cues to identity rise from “unselected” individual differences in vocal morphology or whether they have been accentuated by selection for the purposes of advertising caller identity. By comparing the level of acoustic individuality of different vocalizations within the repertoire of a single species, it is possible to ascertain whether selection for individual recognition has modified the vocal cues to identity in particular contexts. We used discriminant function analyses to determine the level of accuracy with which calls could be classified to the correct individual caller, for three dwarf mongoose (Helogale parvula) vocalizations: contact, snake, and isolation calls. These calls were similar in acoustic structure but divergent in context and function. We found that all three call types showed individual specificity but levels varied with call type (increasing from snake to contact to isolation call). The individual distinctiveness of each call type appeared to be directly related to the degree of benefit that signalers were likely to accrue from advertising their identity within that call context. We conclude that dwarf mongoose signalers have undergone selection to facilitate vocal individual recognition, particularly in relation to the species’ isolation call.
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Although functionally referential signals have been extensively studied, largely in mammals (e.g., nonhuman primates, see Cheney and Seyfarth (1988); mongooses, see Manser et al. (2002); and other ground-dwelling species, see Blumstein and Armitage (1997), other social taxa such as birds would similarly benefit from the use of referential signals. We therefore investigated alarm calling in the cooperative noisy miner (Manorina melanocephala), a species that has been anecdotally recorded producing aerial alarms to flying predators and empirically recorded generating terrestrial alarms to ground-based threats. For these signals to be truly referential however, they must meet 3 criteria. First, calls must be structurally distinct, a requirement that these 2 call types meet. Second, calls must be stimulus-specific and reliably associated with a given stimulus. We tested this on free-living birds by exposing them to a simulated aerial predator that was either in flight or subsequently perched and thus presented one of the first studies on functionally referential alarm systems where both aerial and terrestrial alarm calls have been tested. Miners only produced aerial alarms while the stimulus was in flight, switching to terrestrial alarms once it landed. Third, referential signals must elicit different escape responses that are "appropriate" to the associated threat. Under field conditions, aerial alarm playback alone provoked an almost instantaneous response of fleeing to vegetation cover, whereas terrestrial alarm playback elicited significantly slower responses by receivers and an increase in scanning behavior. During laboratory experiments, aerial alarms stimulated birds to spend more time looking upwards, whereas terrestrial alarm calls stimulated individuals to scan perpendicularly, as expected if these stimuli provided information on likely predator location. Although other avian taxa have been shown to use referential alarm signals, this system provides novel evidence of referential calls based on the behavior rather than the type of predator, providing a highly adaptive means of communicating risk to other members of the social group in this cooperative species. © The Author 2017. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.
Article
Many vertebrates have alarm calls that warn conspecifics about danger, and some species even communicate about the type of predator or its behaviour, allowing for appropriate responses. However, such ‘functionally referential’ communication has been shown experimentally in only a handful of species, and requires demonstrating that individuals give acoustically distinct calls to different threats, and that the calls alone are sufficient to prompt listeners to behave as if a specific threat is present. We carried out model presentations, acoustic analyses and a playback experiment to test whether the alarm calls of noisy miners, Manorina melanocephala, are functionally referential. Miners gave different calls to airborne raptor models compared to terrestrial or perched raptor models, and even switched from ‘aerial’ alarm calls to ‘chur’ alarm calls when a hawk glider landed on the ground. They also behaved differently to these two types of threats, showing avoidance to aerial threats, including fleeing or freezing, but deterrent behaviour to terrestrial threats, including vigilance, approach and mobbing. The two alarm call types were acoustically distinct, and consistent with calls to live predators. Blind scoring of video revealed that birds responded appropriately to playbacks of alarm calls alone, typically fleeing to aerial alarm calls yet becoming vigilant, approaching and calling to chur calls. Noisy miners produce alarm calls that therefore meet both criteria for functional reference, and thus become one of the few bird species in which such calls have been confirmed. Many birds appear to give different calls to airborne predators compared to during mobbing of terrestrial or stationary predators, so functionally referential alarms are likely to be common and may often categorize predators by their behaviour and not simply their taxonomic type.
Article
Communication is an essential component of social interactions between individuals, particularly in larger group sizes. To gain further insight into the factors that underpin cooperative behaviour, herein we examine the acoustic repertoire of the Noisy Miner, Manorina melanocephala, a cooperative species that lives in large colonies. To determine the structure and composition of the Noisy Miner repertoire, we measured the call rates and major acoustic parameters of common vocalisations from colour-banded individuals located at two discrete colonies. A total of 13 different vocalisation types were identified, of which 3 are newly described, with an additional 10 vocalisations being quantified in a new social context. Importantly, we describe a call given only by females and document both sexes producing some calls that were previously thought to be sex-specific. The putative repertoire identified was supported by statistical assessments confirming differences in their spectral and temporal features. Vocalisations were given across a range of social contexts, including the mobbing of predators, aerial alarm vocalisations, apparent maintenance of group cohesion and advertisement of individual location and/or status. This study quantifies the rich vocal repertoire of this social species, and provides further implications for the link between cooperative breeding and large vocal repertoires.
Article
The ability to identify social partners can play a key role in the coordination of social behaviours in group-living animals. Coordinating social behaviours over long distances becomes problematic, as cues to identity are often limited to one or two sensory modalities. This limitation can often select for strong individuality in those cues used for long-distance communication. Pied babblers, Turdoides bicolor, produce a number of different types of ‘loud calls’ which are frequently used to signal to individuals beyond the range of visual or olfactory pathways of communication. Here, we show that three of these ‘loud call’ types, the v-shaped chatter, the double note ascending chatter and the atonal chatter, are each individually distinct. We hypothesise that individuality in the three loud call types tested here may represent a possible pathway to social recognition in this species that may have important consequences for social interactions. However, we also found that the atonal chatter was unstable between years suggesting that this particular call type may not be a reliable long-term indicator to identity which may affect long-term recognition in this species.
Article
Recognition of conspecifics is necessary for differential treatment of individuals in a variety of social contexts, such as territory establishment and defense, dominance hierarchies, reciprocal altruism, mate choice, parent-offspring interactions and nepotistic contexts, to name a few. Here I first review various categories of perceptual mechanisms of social discrimination, focusing largely on the extensive literature on the perception component of kin recognition, although the ideas presented here can and have been used for analyses of recognition at many levels of social organization. I then discuss a range of recognition mechanisms observed in a model species, Belding's ground squirrels, and how socio-ecological factors influence the development and expression of each mechanism. Finally, I address several theoretical and empirical controversies in the kin-recognition literature which pertain to the perceptual component of recognition, as well as areas in need of additional investigation.
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A long-standing question in animal communication is whether signals reveal intrinsic properties of the signaller or extrinsic properties of its environment. Alarm calls, one of the most conspicuous components of antipredator behaviour, intuitively would appear to reflect internal states of the signaller. Pioneering research in primates and fowl, however, demonstrated that signallers may produce unique alarm calls during encounters with different types of predators, suggesting that signallers through selective production of alarm calls provide to conspecific receivers information about predators in the environment. In this article, we review evidence for such functional reference' in the alarm calls of birds based on explicit tests of two criteria proposed in Macedonia & Evans' (Ethology 93, 1993, 177) influential conceptual framework: (1) that unique alarm calls are given to specific predator categories, and (2) that alarm calls isolated from contextual information elicit antipredator responses from receivers similar to those produced during actual predator encounters. Despite the importance of research on birds in development of the conceptual framework and the ubiquity of alarm calls in birds, evidence for functionally referential alarm calls in this clade is limited to six species. In these species, alarm calls are associated with the type of predator encountered as well as variation in hunting behaviour; with defence of reproductive effort in addition to predators of adults; with age-related changes in predation risk; and with strong fitness benefits. Our review likely underestimates the occurrence of functional reference in avian alarm calls, as incomplete application and testing of the conceptual framework has limited our understanding. Throughout, therefore, we suggest avian taxa for future studies, as well as additional questions and experimental approaches that would strengthen our understanding of the meaning of functional reference in avian alarm calls.
Article
A wide range of complex social behaviors are facilitated by the recognition of individual conspecifics. Individual recognition requires sufficient phenotypic variation to provide identity information as well as receivers that process and respond to identity information. Understanding how a complex trait such as individual recognition evolves requires that we consider how each component has evolved. Previous comparative studies have examined phenotypic variability in senders and receiver learning abilities, although little work has compared receiver responses to identity information among related species with and without individual recognition. Here, we compare responses to identity information in two Polistes paper wasps: P. fuscatus, which visually recognizes individuals, and P. metricus, which does not normally show evidence of individual recognition. Although the species differ in individual recognition, the results of this study show that receiver responses to experimentally manipulated identity information are surprisingly similar in both species. Receivers direct less aggression toward identifiable individuals than unidentifiable individuals. Therefore, the responses necessary for individual recognition may pre-date its evolution in the P. fuscatus lineage. Additionally, our data demonstrate the apparent binary differences in a complex behavior between the two species, such as individual recognition, likely involve incremental differences along a number of axes.
Article
Free-ranging vervet monkeys, Cercopithecus aethiops, who had learned to ignore playbacks of one type of call by an unreliable signaller subsequently also ignored playback of an acoustically different call by the same individual if the calls had similar referents. Such transfer did not occur if either the identity of the signaller changed or if the two calls had different referents. After repeatedly being played an intergroup call in the absence of other groups, vervets also ignored an acoustically different intergroup call given by the same individual. The monkeys did not transfer habituation, however, if the new call was given by a different individual. In tests where the referents of two calls were different, the monkeys also failed to transfer habituation across call types. Vervet monkeys who had learned to ignore an unreliable leopard alarm call did not later ignore an eagle alarm call, even when the signaller remained the same. Results suggest that vervets, like humans, process information at a semantic, and not just an acoustic, level.
Article
Seven major types of sampling for observational studies of social behavior have been found in the literature. These methods differ considerably in their suitability for providing unbiased data of various kinds. Below is a summary of the major recommended uses of each technique: In this paper, I have tried to point out the major strengths and weaknesses of each sampling method. Some methods are intrinsically biased with respect to many variables, others to fewer. In choosing a sampling method the main question is whether the procedure results in a biased sample of the variables under study. A method can produce a biased sample directly, as a result of intrinsic bias with respect to a study variable, or secondarily due to some degree of dependence (correlation) between the study variable and a directly-biased variable. In order to choose a sampling technique, the observer needs to consider carefully the characteristics of behavior and social interactions that are relevant to the study population and the research questions at hand. In most studies one will not have adequate empirical knowledge of the dependencies between relevant variables. Under the circumstances, the observer should avoid intrinsic biases to whatever extent possible, in particular those that direcly affect the variables under study. Finally, it will often be possible to use more than one sampling method in a study. Such samples can be taken successively or, under favorable conditions, even concurrently. For example, we have found it possible to take Instantaneous Samples of the identities and distances of nearest neighbors of a focal individual at five or ten minute intervals during Focal-Animal (behavior) Samples on that individual. Often during Focal-Animal Sampling one can also record All Occurrences of Some Behaviors, for the whole social group, for categories of conspicuous behavior, such as predation, intergroup contact, drinking, and so on. The extent to which concurrent multiple sampling is feasible will depend very much on the behavior categories and rate of occurrence, the observational conditions, etc. Where feasible, such multiple sampling can greatly aid in the efficient use of research time.
Article
One suggested anti-predator function of alarm calls is to deliver a message to a predator that it has been detected. Moreover, giving the alarm call could provide a signal to the predator that capturing the individual giving the alarm is more difficult than capturing its silent group members, as the caller is probably the most aware of the predator's location. In an aviary experiment using stuffed dummy Willow Tits Poecile montanus, we assessed whether an authentic alarm call given by Willow Tit affected Pygmy Owl Glaucidium passerinum prey preference. In the experiment, the Owls attacked only the ‘silent’ dummy individuals, suggesting that alarm calling could offer direct fitness benefits to the caller by decreasing the attack risk of the caller relative to its group members.
Article
When using releasers in phylogenetic study, it is essential to consider whether the compared species are sympatric. If they are allopatric, it is often possible to find relationships between all releasers. If they are sympatric it is essential to know something of the function of the releasers, before their taxonomic value can be assessed. Signals that are in some way involved in reproductive isolation are likely to be highly divergent between closely allied sympatric species. They will therefore be useful as characters for specific diagnosis, but of limited value at higher levels of classification. In birds this group will include the male colours of most sexually dimorphic species, especially those that rely on visual recognition, have a short pair bond, and whose reproductive isolation is not yet complete (SIBLEY in press) : also advertisement, pair formation, courtship and some appeasement displays: songs, when they are loud and play an important part in pair-formation: some courtship and perhaps food and nest calls. Releasers of sympatric species whose function discourages specific distinctiveness, will often converge on common types, for the value either of mutually similar signals, or of signals that are for some extrinsic reason most efficient for the context. They are likely to be of limited taxonomic value, even at the specific level. This group includes colours of Batesian and Mullerian mimics; distraction, alarming and aggressive displays used against predators (LACK 1941), alarm calls and displays (HUXLEY 1938) and some nestling and fledgling calls. Releasers selected for moderate specific distinctiveness, with both intra- and inter-specific functions, diverge at a relatively slow rate. They are therefore of little use in specific diagnosis, but are valuable for classifying genera and families. This group includes cryptic colours, especially of female and young; mobbing, pre-flight and aggressive displays; flight and aggressive calls, and some owl-mobbing calls which have secondary functions. A similar moderate specific distinctiveness is found in close-range signals, again valuable in discerning relationships. This group includes colours of eggs and the nestling palate, and perhaps the eye, beak and face colours of adults; some copulatory, submissive and begging displays; soft calls, such as certain alarm cries, and songs which have no function in reproductive isolation, perhaps especially the songs and calls of densely colonial birds.
Article
Adult pale-winged trumpeters produce a varied repertoire of vocalizations: apart from one loud 'tremolo song' we recorded 11 structurally discrete close-range calls, one of which (the 'mew') was individually distinct. There was significant variation across vocalization type with respect to the identity and behaviour of the caller and the response of the receiver(s). It was possible to group vocalizations into six broad contextual classes: alarm, recruitment, social, contact, feeding and territory defence. On detection of danger, trumpeters gave two acoustically different calls, one for aerial predators, and another for terrestrial predators or conspecific intruders. They also produced distinct calls on detection of large prey items such as snakes. These (alarm and snake-finding) call types seemed to evoke different responses by receivers and therefore appeared to be functionally referent. Vocal behaviour was positively correlated with dominance rank and at least two other calls had important roles in mediating social interactions within the group. Finally, the 'mew' call was only given when a trumpeter was separated from, and usually out of visual contact with the rest of the group. This call was functionally referent, eliciting a vocal response from receivers: they produced a loud 'grunt' call, which was also unique to this situation. This is the first experimental demonstration in a bird of the proximate factors motivating production of an individually distinct contact call.
Article
Signature vocalizations contain sufficiently unique spectral and/or temporal identity to allow conspecifics to differentiate between individuals. Experimental assessment of signature content relies on: (1) accurate discrimination of vocalizations according to individual callers using human observers and statistical methods; (2) playback experiments with conspecifics in captivity or in the wild. Signature vocalizations are often acquired through social and vocal learning. Functions for such signals include individual recognition (e.g., between parents and offspring, mating pairs, territorial rivals) and the mediation of social interactions. Signature cues are likely to be subtle, and their analysis is likely to benefit from the use of new data collection technologies and human speech recognition techniques.
Article
The Noisy Miner is a communally breeding Australian honeyeater in which several males feed the offspring of a single female. They reside year‐round in colonies, which may number several hundred birds. Miners within colonies unite to mob predators and are successful in defending their colony area against all other species of birds. The species is also highly aggressive intraspecifically. Individuals in a colony in southeastern Queensland were present most of the time in small activity spaces. Most resident males showed extensive overlap of activity space from one season to the next. Males did not defend their activity spaces, so that coalitions of birds occurred whose membership changed with place and time. Certain assemblages of males, termed coteries, were of a more permanent nature. Coterie members showed aggression towards outsiders at border regions. Females' activity spaces were much smaller and less variable than those of males. They showed almost no overlap and were probably maintained by mutual avoidance. Females tended to nest within the activity space they occupied shortly before the breeding period. Thus the spacing of males and females within a colony was quite different. Interactions, often agonistic, were frequent between individuals, between an individual and a group, and between groups. Encounters involving two males in which participants normally lived farther apart were more often agonistic than when participants lived more closely, and more aggression was seen within coteries than between them. When larger groups of birds had agonistic encounters, they more frequently involved birds from different coteries. Very little male‐female aggression was seen. Interactions between males and females of different coteries were usually sexual, sometimes involving attempted copulation. Colony sizes are probably too large to permit individual recognition of fellow members, but this could be more likely in coteries. Many males in coteries are doubtless closely related, but outsiders frequently infiltrate them. Coteries are not reproductive units.
Article
The extreme coloniality in emperor penguins (Aptenodytes forsteri) demands that (1) individual recognition by the mutual display call must be supremely adapted to the total absence of nest sites — landmarks that would facilitate partner reunion, and (2) birds must transmit a precise message through an obstructed and noisy environment. A computerized sound analysis and subsequent data were submitted to univariate and multivariate statistics to determine individual-specific cues of the call. Temporal patterning of syllables, variables of the power spectrum (frequency and timbre features) and variables of a beat generated by two acoustic sources were analyzed (58 calls from 7 animals). Number and duration of syllables, fundamental frequencies and period of the beat were highly individual, with inter- significantly greater then intra-individual variation, enabling correct classification of the 58 calls. The respective relevance of temporal and spectral cues for individual recognition is discussed. In the acoustically hostile and noisy environment, beat was peculiarly emphasized, as it allowed great precision in the production of an amplitude modulation that was unlikely to be degraded by the environment.
Article
Individual differentiation is usually advantageous in maximising the fitness benefits of interactions with conspecifics. In social species, where intraspecific interactions are frequent, this is likely to be particularly important. Indeed, some form of differentiation underpins most hypotheses proposed to account for cooperative behaviour in birds. The auditory modality is a likely candidate for this function, particularly for species where individuals are widely spaced and in dense vegetation. In this study, we examined the acoustic structure of a distinctive mobbing signal, the ‘chur’ call, of the cooperatively breeding noisy miner Manorina melanocephala. Using 250 calls from 25 individuals, a combination of spectrographic-based measurement of call parameters, cross-correlation and multi-dimensional scaling was used to test for systematic individual differences in call structure. Strong differences between individuals were observed in all measures, indicating that this call encodes sufficient information to facilitate individual differentiation. We then conducted a series of field playbacks to test the effect of the behaviour on conspecifics. Results demonstrated that the call, in isolation, has a clear attractant effect. Given that chur calls are synonymous with the characteristic cooperative mobbing behaviour of this species, these findings suggest they are likely to have an important function in coordinating complex social behaviour.
Article
When foraging in groups, animals can benefit from the collective ability of all foragers to detect predation threats. Upon detection of these threats, individuals may give alarm calls or depart from the group hurriedly, providing indirect clues to other companions that a threat may be imminent even if it has not been detected directly by many. However, false alarms, defined as a misclassification of innocuous threats as real, appear to be very common in birds and mammals. We used a genetic algorithm approach to examine the consequences of false alarms for vigilance and reliance on collective detection. We show that when misclassification errors by detectors occur, antipredator vigilance can decrease along with a lesser reliance on collective detection. We argue that, in such cases, decreased vigilance is needed to ensure that foragers obtain food at a sufficiently high rate to compensate for the time and energy wasted during false alarms. Lesser reliance on collective detection reflects the poorer quality of the information about predation threats conveyed by companions in the group. We also predict that false alarms should increase with group size, thus representing an unappreciated cost of group foraging. We conclude that the occurrence of false alarms could modulate the use of collective detection in gregarious species and influence levels of antipredator vigilance.
Article
Should prey retain an ability to respond to the sight of their extinct predators? The multipredator hypothesis (Blumstein 2006, Ethology, 112, 209–217) assumes that antipredator adaptations evolve together and thus prey may respond to extinct predators as long as they have experience with other predators. We tested this prediction in yellow-bellied marmots, Marmota flaviventris, a species with both extant and extinct predators. Marmots were baited to a predetermined location and then shown one of five life-size photographic stimuli: a medium-size sub-Saharan antelope, the gray duiker, Silvicapra grimmia, as a control stimulus; a red fox, Vulpes vulpes, a low-risk predator; a coyote, Canis latrans, a higher risk predator; a mountain lion, Felis concolor, an extant predator, but one with which our population had no ontogenetic experience; and a wolf, Canis lupus, an extinct predator. Marmots responded differently to each stimulus: they stopped foraging after seeing the duiker, engaged in low vigilance after seeing the fox, seemed to monitor the coyote, fled the wolf, and engaged in high vigilance (and on one occasion alarm-called) in response to the mountain lion. This pattern of responses was consistent with the different risks associated with each species: foxes required monitoring but marmots could generally escape them, coyotes routinely kill adult marmots, solitary hunting mountain lions might be dissuaded from attack once detected, and socially hunting wolves were a very high risk predator, which would be best hidden from. The pattern of responses was not explained simply by stimulus size, stimulus detectability, or stimulus similarity. These results are consistent with the multipredator hypothesis: visual predator discrimination for ontogenetically and evolutionarily novel predators may be maintained in yellow-bellied marmots by extant predation risk.
Article
The first experimental evidence that birds are able to recognize the general voice characteristics of an individual's song repertoire is reported. Five captive male great tits, Parus major, were taught to discriminate between songs from the repertoires of two individuals. They were then tested with unfamiliar songs from the same two birds, which they were able to assign to the correct individual. These results provide a mechanism by which the well-known phenomenon of individual recognition by voice in birds can be achieved.
Article
Early work on loud calling in mammals emphasized the importance of dynamic characteristics such as calling rate as cues to fitness and fighting ability. In contrast, little is known of the potential for fine-scaled acoustic cues to provide receivers with direct information on fitness. Fundamental frequency has typically been considered a good potential indicator of body size in the literature, but resonance frequencies (formants), which should be constrained by the length of the vocal tract, have received less attention. We conducted a detailed acoustic analysis on an extensive database of roars from red deer stags, Cervus elaphus, in a free-ranging population to investigate which variables provided honest information on age, body weight and reproductive success. Although fundamental frequency was higher in young stags than in adults, it did not decrease with body weight within adults and source cues (i.e. those generated by the larynx) in general did not provide clear information on fitness-related characteristics. In contrast, minimum formant frequencies, reached during the part of the roar when the mobile larynx is most fully retracted towards the sternum, decreased with body weight and age and were strongly negatively correlated with our index of reproductive success. Such production-related acoustic cues to body size and fitness, rendered honest by an anatomical constraint limiting the downward movement of the larynx, provide receivers with accurate information that could be used to assess rivals and choose mates. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.
Article
The ability to discriminate among signallers and to respond to them on an individual basis provides receivers with substantial benefits. For example, discriminating among signallers allows receivers to ignore unreliable individuals or to focus their territorial defence on unfamiliar intruders. Such discrimination requires signals to be individually distinctive; that is, signals must vary more among than within individuals. Furthermore, receivers must be able to discriminate among the signals of different individuals. In this study, we used fine structural analysis to show that the simple songs of male black-capped chickadees are individually distinctive, but that substantial variation exists both within and among recordings of the same individual. This finding emphasizes the need for multiple recordings of each individual in studies of individual distinctiveness, since failing to measure variation across recordings of the same individual can make it difficult to determine whether signals vary among individuals or whether they simply vary among different recording sessions. To test whether chickadees discriminate among the signals of different individuals, we used a playback experiment in which we broadcast priming and discrimination stimuli to 45 territorial males. When individuals heard the playback of two different males, they produced more songs and remained near the loudspeaker for a longer period than when they heard two different exemplars from the same male. Chickadees can therefore discriminate among singers based exclusively on their songs, which may help to explain how chickadees eavesdrop on singing contests and subsequently select extrapair mates on the basis of song contest performance.
Article
Alarm calling is a widespread antipredator behaviour. Although the function and evolution of alarm call behaviour have long been studied in detail, only in the last decade has there been an upsurge in research into its development. Here, we review the literature on the development of alarm call production (the delivery of calls with a specific set of acoustic features), alarm call usage (the use of calls in particular contexts) and alarm call responses (the responses to calls produced by others). We detail the mechanistic processes that may underlie the development of each aspect, consider the selection pressures most likely to explain the relative importance of these processes, and discuss the substantial variation in developmental rates found both between and within species. Throughout, we interpret existing findings about age-related differences in alarm call behaviour from two major communicatory viewpoints: the idea that signals carry information from sender to receiver, with young taking time to acquire adult-like skills; and the possibility that signals are used to manage the behaviour of receivers, with young behaving adaptively for their age. We conclude that a broader use of various techniques (e.g. cross-fostering and temporary removals), the formation of stronger collaborative links with other disciplines (e.g. physiology and neurobiology) and the initiation of new research avenues (e.g. kleptoparasitism) will ensure that studies on the development of alarm call behaviour continue to enhance our understanding of such topics as the evolution of communication and language, kin selection and cognitive processing.