Specific Alarm Calls Research Articles

Imagery in wild birds: Retrieval of visual information from referential alarm calls.

Japanese tits (Parus minor) produce specific alarm calls when they encounter a predatory snake. A recent field experiment showed that receiver tits became visually perceptive to an object resembling a snake when hearing these calls. However, the tits did not respond to the same object when hearing other call types or when the object was dissimilar to a snake. These findings provide the first experimental evidence for the retrieval of a visual search image from specific alarm calls, offering a novel approach for investigating the cognitive mechanisms underlying referential communication in wild animals.

Alarm calls evoke a visual search image of a predator in birds

One of the core features of human speech is that words cause listeners to retrieve corresponding visual mental images. However, whether vocalizations similarly evoke mental images in animal communication systems is surprisingly unknown. Japanese tits (Parus minor) produce specific alarm calls when and only when encountering a predatory snake. Here, I show that simply hearing these calls causes tits to become more visually perceptive to objects resembling snakes. During playback of snake-specific alarm calls, tits approach a wooden stick being moved in a snake-like fashion. However, tits do not respond to the same stick when hearing other call types or if the stick's movement is dissimilar to that of a snake. Thus, before detecting a real snake, tits retrieve its visual image from snake-specific alarm calls and use this to search out snakes. This study provides evidence for a call-evoked visual search image in a nonhuman animal, offering a paradigm to explore the cognitive basis for animal vocal communication in the wild.

Out-of-hours doctors' decisions on call-outs in emergency situations.

Several earlier studies have shown that doctors in local out-of-hours emergency primary health care participate in call-outs to varying degrees. It is the out-of-hours doctor who decides whether to respond with a call-out. We wished to study the assessments that form the basis of this decision. We interviewed the out-of-hours doctors in the county of Hordaland who had been alerted about an emergency incident on the health radio network during an evening or night shift, apart from at weekends. The interview period lasted from July to October 2012 and was linked directly to specific alarm calls. There were 252 relevant incidents, 72 of which were investigated. A total of 47 of the 95 doctors contacted were interviewed (49%). The doctor responded with a call-out in 65 % of the incidents. Normally it was the content of the message about the patient's medical condition that was critical for the doctor's decision to respond with a call-out, while it was most often practical aspects that meant that she/he did not respond in this way. When the doctor responded with a call-out, and later assessed the call-out as necessary, the patient's need for medical expertise was the most important reason given. In the incidents studied, the decision on whether or not to respond with a call-out was based on a balanced consideration of the patient's needs and what was practically possible for the doctor. The out-of-hours doctors experienced a need for medical expertise in many emergency medical situations.

Pigeons integrate past knowledge across sensory modalities

Advanced inferring abilities that are used for predator recognition and avoidance have been documented in a variety of animal species that produce alarm calls. In contrast, evidence for cognitive abilities that underpin predation avoidance in nonalarm-calling species is restricted to associative learning of heterospecific alarm calls and predator presence. We investigated cognitive capacities that underlie the perception and computation of external information beyond associative learning by addressing contextual information processing in pigeons, Columba livia, a bird species without specific alarm calls. We used a habituation/dishabituation paradigm across sensory modes to test pigeons' context-dependent inferring abilities. The birds reliably took previous knowledge about predator presence into account and responded with predator-specific scanning behaviour only if predator presence was not indicated before or if the perceived level of urgency increased. Hence, pigeons' antipredator behaviour was not based on the physical properties of displayed stimuli or their referential content alone but on contextual information, indicated by the kind and order of stimulus presentation and different sensory modes.

A micro-geography of fear: learning to eavesdrop on alarm calls of neighbouring heterospecifics

Many vertebrates eavesdrop on alarm calls of other species, which is a remarkable ability, given geographical variation in community composition and call diversity within and among species. We used micro-geographical variation in community composition to test whether individuals recognize heterospecific alarm calls by: (i) responding to acoustic features shared among alarm calls; (ii) having innate responses to particular heterospecific calls; or (iii) learning specific alarm calls. We found that superb fairy-wrens (Malurus cyaneus) fled to cover to playback of noisy miner (Manorina melanocephala) aerial predator alarm calls only in locations where miners were present, suggesting that learning rather than acoustic structure determines response. Sites with and without miners were well within the dispersal distance of fairy-wrens, and philopatric males and dispersing females showed the same pattern, so that local genetic adaptation is extremely unlikely. Furthermore, where miners were present, fairy-wrens responded appropriately to different miner calls, implying eavesdropping on their signalling system rather than fleeing from miners themselves. Learned eavesdropping on alarm calls enables individuals to harvest ecologically relevant information from heterospecifics on an astonishingly fine spatial scale. Such phenotypic plasticity is valuable in a changing world, where individuals can be exposed to new species.

Motivation before Meaning: Motivational Information Encoded in Meerkat Alarm Calls Develops Earlier than Referential Information

In contrast to historical assumptions about the affective nature of animal vocalizations, it is now clear that many vertebrates are capable of producing specific alarm calls in response to different predators, calls that provide information that goes beyond the motivational state of a caller. However, although these calls function referentially, it does not mean that they are devoid of motivational content. Studies on meerkats (Suricata suricatta) directly support this conclusion. The acoustic structure of their alarm calls simultaneously encodes information that is both motivational (level of urgency) and referential (predator specific). In this study, we investigated whether alarm calls of young meerkats undergo developmental modification and whether the motivational or the referential aspect of calls changes more over time. We found that, based on their acoustic structure, calls of young showed a high correct assignment to low- and high-urgency contexts but, in contrast to adults, low assignment to specific predator types. However, the discrimination among predator types was better in high-urgency than in low-urgency contexts. Our results suggest that acoustic features related to level of urgency are expressed earlier than those related to predator-specific information and may support the idea that referential calls evolve from motivational signals.

Responses of Redfronted Lemurs to Experimentally Modified Alarm Calls: Evidence for Urgency‐Based Changes in Call Structure

Abstract The aim of this study was to investigate how information about the affective state is expressed in vocalizations. Alarm calls can serve as model systems with which to study this general question. Therefore, we examined the information content of terrestrial predator alarm calls of redfronted lemurs (Eulemur fulvus rufus), group‐living Malagasy primates. Redfronted lemurs give specific alarm calls only towards raptors, whereas calls given in response to terrestrial predators (woofs) are also used in other situations characterized by high arousal. Woofs may therefore have the potential to express the perceived risk of a given threat. In order to examine whether different levels of arousal are expressed in call structure, we analysed woofs given during inter‐group encounters or in response to playbacks of a barking dog, assuming that animals engaged in inter‐group encounters experience higher arousal than during the playbacks of dog barks. A multivariate acoustic analysis revealed that calls given during group encounters were characterized by higher frequencies than calls given in response to playbacks of dog barks. In order to examine whether this change in call structure is salient to conspecifics, we conducted playback experiments with woofs, modified in either amplitude or frequencies. Playbacks of calls with increased frequency or amplitude elicited a longer orienting response, suggesting that different levels of arousal are expressed in call structure and provide meaningful information for listeners. In conclusion, the results of our study indicate that the information about the sender's affective state is expressed in the structure of vocalizations.

Anti-predator behavior of group-living Malagasy primates: mixed evidence for a referential alarm call system

Many mammals warn conspecifics with alarm calls about detected predators. These alarm calls are either functionally referential, urgency based, or they can have multiple functions, including predator deterrence. The taxonomic distribution of these alarm call systems is uneven, with primates providing the best-known examples for a functionally referential system and rodents most examples of an urgency-based system. Reports of different alarm call systems in lemurid primates prompted us to examine the anti-predator behavior of two additional lemur species. In an experimental field study we exposed adult redfronted lemurs (Eulemur fulvus rufus) and white sifakas (Propithecus verreauxi verreauxi) to playbacks of vocalizations of their main aerial and terrestrial predators, as well as to their own alarm calls given in response to the presentation of these predators. We scored the subjects' immediate behavioral responses, including alarm calls, from video recordings made during the first minute following a playback. We found that both species gave specific alarm calls only in response to raptor playbacks and the corresponding alarm calls, whereas calls given in response to carnivores and the corresponding alarm calls were also observed in other situations characterized by high arousal. Other behavioral responses, such as gaze and escape directions, corresponded to the hunting strategies of the two predator classes, suggesting that the corresponding vocalizations were categorized correctly. These two lemur species, which represent different families, have therefore independently evolved a mixed alarm call system, characterized by functionally referential calls for diurnal raptors, but not for carnivores. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00265-001-0436-0

Red squirrels,Tamiasciurus hudsonicus, produce predator-class specific alarm calls

Red squirrels, can produce alarm calls when they detect a potential predator. Observations of natural interactions between red squirrels and large birds, and predator-presentation experiments in the field, showed that red squirrels produce acoustically different alarm calls in response to aerial danger (live birds and a model hawk flown towards them) versus danger approaching from the ground (dogs and humans). The alarm call produced in response to aerial danger is acoustically convergent on the ‘seet’ alarm call produced by many species of passerine birds in response to raptors. The squirrels' ‘seet’ alarm is a short, low-amplitude, high-frequency call. These characteristics make the call difficult to localize, and is in a frequency range that is poorly perceived by raptors. Red squirrels produce much louder, wide-bandwidth bark calls in response to terrestrial danger. This is the first demonstration of predator-class specific alarm calls of red squirrels.

Golden‐marmot Alarm Calls. II. Asymmetrical Production and Perception of Situationally Specific Vocalizations?

AbstractMany species produce alarm calls that vary according to situation. An implicit assumption for these species is that production and perception of situationally specific alarm calls is symmetrical: perceivers respond to variation produced by signalers. The companion paper to this one (Blumstein 1995) showed that golden marmots (Marmota caudata aurea) produce variable alarm calls that vary in proportion to the degree of risk the caller perceives. Calls produced in higher‐risk situations have fewer notes than calls produced in lower‐risk situations. In this study, to determine the salience of the number of notes per call in eliciting different responses in conspecific perceivers, I played back three‐note alarm calls, eight‐note alarm calls, and the non‐alarm vocalization of a local bird to adult golden marmots. Although marmots responded differently to bird calls and alarm calls, vigilance responses to the different alarm calls were similar. Several explanations may account for the apparent insensitivity to alarm‐call variation: golden marmots may require additional contextual cues to properly interpret alarm calls, perceptual abilities do not parallel production abilities, or calls may serve a generalized alerting function.