Antipredator Calls Research Articles

Referential alarm calling elicits future vigilance in a host of an avian brood parasite.

Yellow warblers (Setophaga petechia) use referential 'seet' calls to warn mates of brood parasitic brown-headed cowbirds (Molothrus ater). In response to seet calls during the day, female warblers swiftly move to sit tightly on their nests, which may prevent parasitism by physically blocking female cowbirds from inspecting and laying in the nest. However, cowbirds lay their eggs just prior to sunrise, not during daytime. We experimentally tested whether female warblers, warned by seet calls on one day, extend their anti-parasitic responses into the future by engaging in vigilance at sunrise on the next day, when parasitism may occur. As predicted, daytime seet call playbacks caused female warblers to leave their nests less often on the following morning, relative to playbacks of both their generic anti-predator calls and silent controls. Thus, referential calls do not only convey the identity or the type of threat at present but also elicit vigilance in the future to provide protection from threats during periods of heightened vulnerability.

Australian magpies adjust their alarm calls according to predator distance

ABSTRACT Many animals produce antipredator calls in response to the presence of a predator, which, in some species, can provide information about the distance to predator. Although previous research has shown that several bird species are able to encode information about predator distance in their calls, such information is still lacking for a range of species. Moreover, most previous research has categorised the distance between the caller and the predator in two classes (close and far), but subtle acoustic variation can occur within each distance class. We investigate whether calls given by the Western Australian magpie varied according to predator distance. By presenting a taxidermied predator to a population of magpies at different distances, we found that calls varied according to predator distance from the caller, with more calls being produced when the predator was closer. In addition, we found that calls given in response to a predator nearby are acoustically different from those given in response to the same predator further away. This way of encoding information may allow prey to more efficiently moderate antipredator behaviours according to the level of threat.

Ultrasound use by Sunda colugos offers new insights into the communication of these cryptic mammals

Recent reports of the use of ultrasound for communication by nocturnal mammals have expanded our understanding of behaviour in these animals. The vocal repertoire of colugos has so far only been known to include audible sound. Here, we report the use of ultrasound calls by Sunda colugos (Galeopterus variegatus, order Dermoptera). We recorded one type of call emitted by seven individuals with mean individual frequencies between 37.4 ± 0.6 and 39.2 ± 0.7 kHz during its maximum energy and lasting 28.7 ± 1.6 to 46.9 ± 21.1 ms. Each call showed 3–36 sequential pulses with individual mean interpulse intervals between 423.0 ± 101.4 and 1230.0 ± 315.4 ms. High frequency calls may serve as cryptic anti-predator alarm calls. Our observations suggest that more species of nocturnal mammals may use ultrasound to communicate, and that further studies are needed to determine the occurrence, function and diversity of these calls.

Peahens can differentiate between the antipredator calls of individual conspecifics

Animals of many different species discriminate among individuals based on acoustic properties of vocalizations. These vocalizations are produced in different contexts, including territorial defence and parent–offspring interactions. They are also produced in response to predators, but we know less about whether animals, especially birds, are able to discriminate among individuals based on antipredator calls. We therefore examined whether an avian species (peafowl, Pavo cristatus) is able to differentiate between the antipredator calls of different individuals. Using a habituation–discrimination playback paradigm, we habituated peahens to the antipredator calls of a given individual and then examined their responses to additional calls from that individual and to calls from a novel individual. We found that peahens responded more strongly to calls from the novel individual than from the original individual, demonstrating that they are able to differentiate between individuals based on the acoustic properties of antipredator calls. The ability to differentiate between individual callers may be useful to peahens in modifying their antipredator behaviour based on signaller reliability.

Aposematism and crypsis in a rodent: antipredator defence of the Norwegian lemming

Aposematism is unusual in herbivorous mammals, and exceptions help clarify its ecology and evolution. The Norwegian lemming differs from other rodents in colouration and behaviour. One hypothesis is that its black, yellow and white colours, loud calls and ferocious defence reduce predation by conspicuous aposematism. Another hypothesis is that the colouration is cryptic. These alternatives are tested in a detectability experiment comparing lemmings and sympatric grey-sided voles. All 18 observers detected a higher proportion of the lemmings, corroborating conspicuousness. Unlike smaller rodents, Norwegian lemmings often call from a distance at predators. The aposematism hypothesis predicts that cryptically coloured Alaskan brown lemmings will not call. In the field, Norwegian lemmings gave antipredator calls at a human observer in 36 of 110 encounters, but brown lemmings did so in only 1 of 39 cases. Most Norwegian lemmings called if surprised within a few metres but froze or fled silently farther away, relying on crypsis against distant predators. Small juveniles called as often as adults, a possible case of auto-mimicry. In an earlier experiment, Norwegian lemmings, in contrast with grey-sided voles, aggressively resisted attacks by a major avian predator of rodents. The tests corroborate the hypotheses that (1) distinctive, contrast-rich colouration, antipredator calls and threat postures of the Norwegian lemming form a multimodal suit of aposematic traits, warning predators that this is a more dangerous prey than the smaller sympatric voles, and (2) discriminability from undefended species is an important adaptive reason for conspicuous distinctness of many aposematic signals.

Nestling use of alternative acoustic antipredator responses is related to immune condition and social context

Birds present a variety of antipredator responses, including the use of acoustic signals that may be directed to other individuals or to the predator. We tested competing hypotheses regarding antipredator responses by analysing patterns of variation in the use of distress calls in campo flicker, Colaptes campestris campestris, nestlings. More specifically, we tested whether immune response and social context (presence or absence of other individuals of the social group) were associated with variation in use of acoustic signals in response to human handling. Individuals with higher immunocompetence used proportionally more harsh, low-pitched calls (‘scream’ notes) than individuals with lower immunocompetence, while the latter used mostly tonal, high-pitched calls (‘week’ notes); in both cases there was no influence of the social context on call type. Individuals responded to the social context by giving fewer scream notes and week notes in the presence of adults of the social group than when the adults were absent. Although playbacks are necessary to determine the function of the calls, our results indicate that campo flicker nestling antipredator calls could be used to attract other individuals of the group to help defend the nestling. Also, the use of proportionally more scream notes by healthier individuals suggests that these notes could act as an honest signal of the nestlings’ physiological condition.

Peafowl antipredator calls encode information about signalers.

Animals emit vocalizations that convey information about external events. Many of these vocalizations, including those emitted in response to predators, also encode information about the individual that produced the call. The relationship between acoustic features of antipredator calls and information relating to signalers (including sex, identity, body size, and social rank) were examined in peafowl (Pavo cristatus). The "bu-girk" antipredator calls of male and female peafowl were recorded and 20 acoustic parameters were automatically extracted from each call. Both the bu and girk elements of the antipredator call were individually distinctive and calls were classified to the correct signaler with over 90% and 70% accuracy in females and males, respectively. Females produced calls with a higher fundamental frequency (F0) than males. In both females and males, body size was negatively correlated with F0. In addition, peahen rank was related to the duration, end mean frequency, and start harmonicity of the bu element. Peafowl antipredator calls contain detailed information about the signaler and can potentially be used by receivers to respond to dangerous situations.

Searching for the Audience of the Weeping Lizard's Distress Call

AbstractThe evolution and functions of avian and mammalian antipredator calls are well understood, which contrasts with a lack of progress in reptiles. Here, we present the first investigation of the functions of a distress call in a lizard. We studied Liolaemus chiliensis, which emits a short and complex high‐pitched scream when it is subdued. We determined the behavioral responses of two potential targets to these calls, conspecifics, and a snake predator. Additionally, we tested whether the chemical environment (presence of chemical scents from conspecifics) modulates the lizards' responses to calls. Both the conspecifics and the predator responded to the distress calls, which triggered a longer period of immobility in the lizards and a reduction in exploratory behavior in the snake, as compared to a white noise. In addition, the lizards in the arena with scents of conspecifics responded to distress calls and noise with more movements and escape attempts. These results suggest that distress calls may enhance the survival of L. chiliensis individuals.

Referential mobbing calls elicit different predator-searching behaviours in Japanese great tits

Individuals of many avian and mammalian species produce antipredator calls when they encounter a predator. These calls often vary in acoustic structure depending on the type or level of predation risk, thereby eliciting the appropriate escape responses in conspecifics. Such complexity in communication may also be advantageous in situations in which animals recruit other individuals to mob predators because different risks may sometimes require different mobbing responses. I tested this idea in Japanese great tits, Parus major minor, which produce acoustically distinct mobbing calls for two different nest predators: ‘chicka’ calls for jungle crows, Corvus macrorhynchos, and ‘jar’ calls for Japanese rat snakes, Elaphe climacophora. A playback experiment revealed that adult great tits responded to different mobbing calls with qualitatively different behaviours: they scanned the horizon in response to ‘chicka’ calls and gazed towards the ground in response to ‘jar’ calls. These two responses help adults search for and detect the corresponding predators since crows fly to the nest and snakes approach from the ground. This study demonstrates that the mobbing calls of Japanese great tits transmit referential information about predator types and elicit the appropriate predator-searching behaviours in adults.

The difference between night and day: antipredator behavior in birds

Animals have evolved sophisticated strategies for avoiding predators during the day. These strategies can vary depending on the type of predator and level of threat. Although nocturnal predation is a major cause of animal mortality, antipredator behavior at night is poorly under- stood. To investigate how diurnal animals adjust their anti- predator behavior during these different conditions, peahens (Pavo cristatus) were exposed to a taxidermy raccoon during the daytime and nighttime. During the day, the peahens emitted loud antipredator calls, extended their necks upward, adopted a preflight posture, and approached the predator; at night, the peahens emitted soft hissing calls, remained sta- tionary, piloerected their feathers, and raised their tails. The results demonstrate that birds adopt radically different anti- predator behavior depending on whether the threat occurs in the daytime or nighttime. These different tactics could result from limitations in sensory abilities. Videos showing noc- turnal and diurnal antipredator behavior of peafowl are available online (http://www.momo-p.com/showdetail-e. php?movieid=momo111110pc01a and http://www.momo- p.com/showdetail-e.php?movieid=momo111110pc02a).

Antipredator calls of tufted titmice and interspecific transfer of encoded threat information

Birds in family Paridae (titmice and chickadees) produce complex and distinct alarm vocalizations in response to predator encounters. In 2 controlled aviary experiments, we tested for information transfer between 2 different species of parids. We first recorded the vocal and nonvocal alarm displays of captive tufted titmouse (Baeolophus bicolor) flocks responding to presentations of live predators and controls (no animal and quail). Second, we broadcast the recorded titmouse vocalizations to captive Carolina chickadees (Poecile carolinensis) and recorded their vocal and nonvocal responses. By evaluating the situational specificity of responses by, both, titmice (production specificity, H1) and chickadees (response specificity, H2) to their respective treatments, we could test for information transfer (H3) from titmice to chickadees. Analyses revealed that information content encoded in titmouse calls completely distinguished the different predation threats presented to them (confirming H1). Similarly, chickadee responses clearly distinguished the different predator threats encoded in titmouse calls they heard (confirming H2). Responses of the 2 species were, both, parallel and threat appropriate, confirming that heterospecific information transfer occurred (from titmice to chickadees; H3). Evidence abounds that parids convey important facilitative benefits to other species within Holarctic forest bird communities. We propose that information sharing about predation threats may underlie these benefits for species that participate in communication networks with parids and suggest titmice function as community informants. Key words: alarm calls, chickadee, heterospecific information transfer, mobbing, production and perception specificity, titmouse. [Behav Ecol]

Leadership of Winter Mixed-Species Flocks by Tufted Titmice (Baeolophus bicolor): Are Titmice Passive Nuclear Species?

The tufted titmouse (Baeolophus bicolor, TUTI) is a nuclear species in winter foraging flocks whose antipredator calls are used to manage predation risk by diverse heterospecifics. We hypothesized that satellite species in mixed flocks follow TUTI (not vice versa), thereby defining the role of TUTI as a “passive” nuclear species. We followed 20 winter mixed-species flocks in North-Central Florida and assessed angular-angular correlations between overall flock, TUTI, and satellite species movement directions. We observed significant correlations between overall flock movement directions and those of TUTI, confirming our central prediction. Within flocks, however, fine-scale movement directions of satellite species were often more highly correlated with those of other satellites than with TUTI movements. We conclude that TUTI are passive nuclear species whose movements define flock paths, but within flocks, TUTI movements may have less influence on satellite movements than do other factors.

Animals in translation: why there is meaning (but probably no message) in animal communication

Birds present a variety of antipredator responses, including the use of acoustic signals that may be directed to other individuals or to the predator. We tested competing hypotheses regarding antipredator responses by analysing patterns of variation in the use of distress calls in campo flicker, Colaptes campestris campestris, nestlings. More specifically, we tested whether immune response and social context (presence or absence of other individuals of the social group) were associated with variation in use of acoustic signals in response to human handling. Individuals with higher immunocompetence used proportionally more harsh, low-pitched calls (‘scream’ notes) than individuals with lower immunocompetence, while the latter used mostly tonal, high-pitched calls (‘week’ notes); in both cases there was no influence of the social context on call type. Individuals responded to the social context by giving fewer scream notes and week notes in the presence of adults of the social group than when the adults were absent. Although playbacks are necessary to determine the function of the calls, our results indicate that campo flicker nestling antipredator calls could be used to attract other individuals of the group to help defend the nestling. Also, the use of proportionally more scream notes by healthier individuals suggests that these notes could act as an honest signal of the nestlings' physiological condition.

Birds adjust acoustic directionality to beam their antipredator calls to predators and conspecifics

Animals in many vertebrate species vocalize in response to predators, but it is often unclear whether these antipredator calls function to communicate with predators, conspecifics or both. We evaluated the function of antipredator calls in 10 species of passerines by measuring the acoustic directionality of these calls in response to experimental presentations of a model predator. Acoustic directionality quantifies the radiation pattern of vocalizations and may provide evidence about the receiver of these calls. We predicted that antipredator calls would have a lower directionality if they function to communicate with surrounding conspecifics, and a higher directionality and aimed at the receiver if they function to communicate with the predator. Our results support both of these functions. Overall, the birds produce antipredator calls that have a relatively low directionality, suggesting that the calls radiate in many directions to alert conspecifics. However, birds in some species increase the directionality of their calls when facing the predator. They can even direct their calls towards the predator when facing lateral to it--effectively vocalizing sideways towards the predator. These results suggest that antipredator calls in some species are used to communicate both to conspecifics and to predators, and that birds adjust the directionality of their calls with remarkable sophistication according to the context in which they are used.

Monkeys crying wolf? Tufted capuchin monkeys use anti-predator calls to usurp resources from conspecifics

The use of 'tactical deception' is argued to have been important in the cognitive evolution of the order Primates, but systematic studies of active deception in wild non-human primates are scant. This study tests whether wild tufted capuchin monkeys (Cebus apella nigritus) use alarm calls in a functionally deceptive manner to usurp food resources. If capuchins use alarm calls 'deceptively', it was predicted that false alarms should be: (i) given by subordinates more than by dominants, (ii) more frequent when food is most contestable, (iii) more frequent when less food is available, and (iv) given when the caller is in a spatial position in which it could increase its feeding success if conspecifics react to the call. These predictions were tested by observing subjects in experimental contexts, in which the amount and distribution of a high-value resource (banana pieces) were manipulated using wooden platforms suspended from tree branches. While false alarms were non-significantly more common when more food was available, the three remaining predictions were supported. These results generally support the hypothesis that alarm calls are used by capuchins to reduce the effects of feeding competition. Whether this is intentional on the part of the caller requires further investigation.

Mobbing calls signal predator category in a kin group-living bird species

Many prey species gather together to approach and harass their predators despite the associated risks. While mobbing, prey usually utter calls and previous experiments have demonstrated that mobbing calls can convey information about risk to conspecifics. However, the risk posed by predators also differs between predator categories. The ability to communicate predator category would be adaptive because it would allow other mobbers to adjust their risk taking. I tested this idea in Siberian jays Perisoreus infaustus, a group-living bird species, by exposing jay groups to mounts of three hawk and three owl species of varying risks. Groups immediately approached to mob the mount and uttered up to 14 different call types. Jays gave more calls when mobbing a more dangerous predator and when in the presence of kin. Five call types were predator-category-specific and jays uttered two hawk-specific and three owl-specific call types. Thus, this is one of the first studies to demonstrate that mobbing calls can simultaneously encode information about both predator category and the risk posed by a predator. Since antipredator calls of Siberian jays are known to specifically aim at reducing the risk to relatives, kin-based sociality could be an important factor in facilitating the evolution of predator-category-specific mobbing calls.

Referential Calls Signal Predator Behavior in a Group-Living Bird Species

Predation is a powerful agent of natural selection, driving the evolution of antipredator calls [1]. These calls have been shown to communicate predator category [2-4] and/or predator distance to conspecifics [5-7]. However, the risk posed by predators depends also on predator behavior [8], and the ability of prey to communicate predator behavior to conspecifics would be a selective advantage reducing their predation risk. I tested this idea in Siberian jays (Perisoreus infaustus), a group-living bird species. Predation by hawks, and to a lesser extent by owls, is substantial and the sole cause of mortality in adult jays [9]. By using field data and predator-exposure experiments, I show here that jays used antipredator calls for hawks depending on predator behavior. A playback experiment demonstrated that these prey-to-prey calls were specific to hawk behavior (perch, prey search, attack) and elicited distinct, situation-specific escape responses. This is the first study to demonstrate that prey signals convey information about predator behavior to conspecifics. Given that antipredator calls in jays aim at protecting kin group members [10, 11], consequently lowering their mortality [9], kin-selected benefits could be an important factor for the evolution of predator-behavior-specific antipredator calls in such systems.

Vocal Response of Captive-reared Saguinus oedipus During Mobbing

Mobbing is an important component of antipredator behavior for animals from many taxa. Callitrichids are small-bodied primates that mob multiple types of predators. Though there have been several observations of callitrichids mobbing predators in the wild, their anecdotal nature provides only rough descriptions of behavior and vocalizations. Researchers could neither spectrographically identify nor quantify vocalizations owing to the limitations of observing predation in the field. We examined in detail the mobbing response of 1 callitrichid species, the cotton-top tamarin, in captivity. We recorded vocalizations for quantitative analysis and observed behavior qualitatively. We report 3 new vocalizations that had not been described in the original repertoire for the cotton-top tamarin. Analysis of the time course of a mobbing session yielded a pattern in which the highest intensity mobbing vocalizations decreased over the session even though lower intensity vocalizing continued, which may reflect a shifting strategy from mobbing to vigilance. The rate of calling during mobbing sessions differed from the rate of calling during control sessions. We discuss the vocalizations in relation to 2 hypotheses of form and function of antipredator calls. The newly described mobbing vocalizations may have an important impact on the study of mobbing because they represent a class of vocalizations that researchers have largely ignored in studies of callitrichids, thus raising new issues concerning past and future research on antipredator behavior in the family.

Variable specificity in the anti-predator vocalizations and behaviour of the white-faced capuchin, Cebus capucinus

Much research in animal communication is aimed at understanding the functional design features of animal vocal signals. Our detailed analyses of the vocalizations and behavioural responses elicited in white-faced capuchins by predators and other disturbances point to two call variants that differ modestly in their acoustic structure and that are accompanied by functionally distinct behavioural responses. The first variant is given exclusively to avian predators and is almost invariably accompanied by the monkey's immediate descent from the treetops where it is most vulnerable; therefore, we label this call variant the 'aerial predator alarm'. The second variant, that differs only slightly but noticeably from the first, is given to a wide range of snakes and mammals, including a range of species that represent no predatory threat to the monkeys. This second call is also associated with more variable responses from calling monkeys, from delayed retreat from the source of disturbance, to active approach, inspection, and sometimes mobbing of the animal involved. We therefore label this variant more generally as an 'alerting call'. Although some other primate species show a more diverse system of anti-predator calls, and the capuchins themselves may yet be found to produce a greater variety of calls, a system of two call variants with varying degrees of predator specificity and behavioural response is not uncommon among primates and appears functionally appropriate for capuchins. The basic structure of the alerting call allows conspecific listeners to localize the caller and the source of disturbance readily, thereby allowing listeners to approach and assist in mobbing in cases where the disturbance warrants it, or to avoid the area in cases where the disturbance is identified as a predatory threat. Conversely, the aerial predator alarm is inherently less localizable and therefore conveys the presence of a predator to conspecific listeners nearby while allowing the signaler itself to remain relatively inconspicuous.

Habitat structure and alarm call dialects in Gunnison's prairie dog (Cynomys gunnisoni)

We examined the relationship between habitat structure and alarm call characteristics in six colonies of Gunnison's prairie dogs (Cynomys gunnisoni) near Flagstaff, Arizona, before and after a mid-summer vegetation change. We found significant differences in alarm call characteristics between colonies, confirming the existence of alarm call dialects. Differences in frequency components but not temporal components of calls were associated with differences in habitat structure. Playback experiments revealed that differences in alarm call structure affected acoustic transmission of calls through the local habitat. Thus, we identify habitat structure as one factor that may contribute to alarm call differences between colonies of Gunnison's prairie dogs. Relationships between call characteristics and habitat structure changed over seasons. Playback experiments suggested that this changing relationship could reflect a change in the purpose of the alarm call between early and late summer. Some components of alarm calls seem tailored for attenuation over short distances in the early summer but for long-distance transmission at summer's end. These differences might arise because pups stay close to their natal burrows in the early summer and disperse throughout a colony in late summer. Alternatively, these differences in alarm call transmission between seasons could be caused by the increase in vegetation in the mid-summer. At the end of the summer prairie dogs could be more dependent on long-distance antipredator calls to offset the loss of visibility caused by the increase in vegetation in the late summer. Copyright 2002.