Heterospecific Calls Research Articles

Functional neurogenomic responses to acoustic threats, including a heterospecific referential alarm call and its referent, in the auditory forebrain of red-winged blackbirds

In animal communication, functionally referential alarm calls elicit the same behavioral responses as their referents, despite their typically distinct bioacoustic traits. Yet the auditory forebrain in at least one songbird species, the black-capped chickadee Poecile atricapillus, responds similarly to threat calls and their referent predatory owl calls, as assessed by immediate early gene responses in the secondary auditory forebrain nuclei. Whether and where in the brain such perceptual and cognitive equivalence is processed remains to be understood in most other avian systems. Here, we studied the functional neurogenomic (non-) equivalence of acoustic threat stimuli perception by the red-winged blackbird Agelaius phoeniceus in response to the actual calls of the obligate brood parasitic brown-headed cowbird Molothrus ater and the referential anti-parasitic alarm calls of the yellow warbler Setophaga petechia, upon which the blackbird is known to eavesdrop. Using RNA-sequencing from neural tissue in the auditory lobule (primary and secondary auditory nuclei combined), in contrast to previous findings, we found significant differences in the gene expression profiles of both an immediate early gene, ZENK (egr-1), and other song-system relevant gene-products in blackbirds responding to cowbird vs. warbler calls. In turn, direct cues of threats (including conspecific intruder calls and nest-predator calls) elicited higher ZENK and other differential gene expression patterns compared to harmless heterospecific calls. These patterns are consistent with a perceptual non-equivalence in the auditory forebrain of adult male red-winged blackbirds in response to referential calls and the calls of their referents.

Noise constrains heterospecific eavesdropping more than conspecific reception of alarm calls.

Many vertebrates eavesdrop on alarm calls of other species, as well as responding to their own species' calls, but eavesdropping on heterospecific alarm calls might be harder than conspecific reception when environmental conditions make perception or recognition of calls difficult. This could occur because individuals lack hearing specializations for heterospecific calls, have less familiarity with them, or require more details of call structure to identify calls they have learned to recognize. We used a field playback experiment to provide a direct test of whether noise, as an environmental perceptual challenge, reduces response to heterospecific compared to conspecific alarm calls. We broadcast superb fairy-wren (Malurus cyaneus) and white-browed scrubwren (Sericornis frontalis) flee alarm calls to each species with or without simultaneous broadcast of ambient noise. Using two species allows isolation of the challenge of heterospecific eavesdropping independently of any effect of call structure on acoustic masking. As predicted, birds were less likely to flee to heterospecific than conspecific alarm calls during noise. We conclude that eavesdropping was harder in noise, which means that noise could disrupt information on danger in natural eavesdropping webs and so compromise survival. This is particularly significant in a world with increasing anthropogenic noise.

Both learning and syntax recognition are used by great tits when answering to mobbing calls

Abstract Mobbing behavior, in addition to its complex cooperative aspects, is particularly suitable to study the mechanisms implicated in heterospecific communication. Indeed, various mechanisms ranging from pure learning to innate recognition have been proposed. One promising yet understudied mechanism could be syntax recognition, especially given the latest works published on syntax comprehension in birds. In this experiment, we test whether great tits use both learning and syntax recognition when responding to heterospecifics. In the first part of the experiment, we demonstrate that great tits show different responses to the same heterospecific calls depending on their sympatric status. In the second part, we explore the impact of reorganizing the notes of the heterospecific mobbing calls to fit the syntax of great tits. Great tits showed an increased mobbing response toward the heterospecific calls when they shared their own call organization. Our results corroborate the recent finding that syntactic rules in bird calls may have a strong impact on their communication systems and enlighten how various mechanisms can be used by the same species to respond to heterospecific calls.

The evolution of eavesdropping on heterospecific alarm calls: Relevance, reliability, and personal information.

Interceptive eavesdropping on the alarm calls of heterospecifics provides crucial information about predators. Previous research suggests predator discrimination, call relevance, reliability, and reception explain when eavesdropping will evolve. However, there has been no quantitative analysis to scrutinize these principles, or how they interact. We develop a mathematical framework that formalizes the study of the key principles thought to select for eavesdropping. Interceptive eavesdropping appears to be greatly affected by the threat faced by caller and eavesdropper, as well as presence of informational noise affecting the detection of calls and predators. Accordingly, our model uses signal detection theory to examine when selection will favor alarm calling by a sender species and fleeing by an eavesdropping receiver species. We find eavesdropping is most strongly selected when (1) the receiver faces substantial threats, (2) species are ecologically similar, (3) senders often correctly discriminate threats, (4) receivers often correctly perceive calls, and (5) the receiver's personal discrimination of threats is poor. Furthermore, we find (6) that very high predation levels can select against eavesdropping because prey cannot continuously flee and must conserve energy. Reliability of heterospecific calls for identifying threats is thought to be important in selecting for eavesdropping. Consequently, we formally define reliability, showing its connection to specificity and sensitivity, clarifying how these quantities can be measured. We find that high call relevance, due to similar vulnerability to predators between species, strongly favors eavesdropping. This is because senders trade-off false alarms and missed predator detections in a way that is also favorable for the eavesdropper, by producing less of the costlier error. Unexpectedly, highly relevant calls increase the total number of combined errors and so have lower reliability. Expectedly, when noise greatly affects personally gathered cues to threats, but not heterospecific calls or detection of predators, eavesdropping is favored.

The ABC-D of animal linguistics: are syntax and compositionality for real?

In several animal species, an alarm call (e.g. ABC notes in the Japanese tit Parus minor) can be immediately followed by a recruitment call (e.g. D notes) to yield a complex call that triggers a third behaviour, namely mobbing. This has been taken to be an argument for animal syntax and compositionality (i.e. the property by which the meaning of a complex expression depends on the meaning of its parts and the way they are put together). Several additional discoveries were made across species. First, in some cases, animals respond with mobbing to the order alarm-recruitment but not to the order recruitment-alarm. Second, animals sometimes respond similarly to functionally analogous heterospecific calls they have never heard before, and/or to artificial hybrid sequences made of conspecific and heterospecific calls in the same order, thus adding an argument for the productivity of the relevant rules. We consider the details of these arguments for animal syntax and compositionality and argue that, with one important exception (Japanese tit ABC-D sequences), they currently remain ambiguous: there are reasonable alternatives on which each call is a separate utterance and is interpreted as such ('trivial compositionality'). More generally, we propose that future studies should argue for animal syntax and compositionality by explicitly pitting the target theory against two deflationary analyses: the 'only one expression' hypothesis posits that there is no combination in the first place, for example just a simplex ABCD call; while the 'separate utterances' hypothesis posits that there are separate expressions (e.g. ABC and D), but that they form separate utterances and are neither syntactically nor semantically combined.

Cerebral Activity in Female Baboons (Papio anubis) During the Perception of Conspecific and Heterospecific Agonistic Vocalizations: a Functional Near Infrared Spectroscopy Study

The “voice areas” in the superior temporal cortex have been identified in both humans and non-human primates as selective to conspecific vocalizations only (i.e., expressed by members of our own species), suggesting its old evolutionary roots across the primate lineage. With respect to non-human primate species, it remains unclear whether the listening of vocal emotions from conspecifics leads to similar or different cerebral activations when compared to heterospecific calls (i.e., expressed by another primate species) triggered by the same emotion. Using a neuroimaging technique rarely employed in monkeys so far, functional Near Infrared Spectroscopy, the present study investigated in three lightly anesthetized female baboons (Papio anubis), temporal cortex activities during exposure to agonistic vocalizations from conspecifics and from other primates (chimpanzees—Pan troglodytes), and energy matched white noises in order to control for this low-level acoustic feature. Permutation test analyses on the extracted OxyHemoglobin signal revealed great inter-individual differences on how conspecific and heterospecific vocal stimuli were processed in baboon brains with a cortical response recorded either in the right or the left temporal cortex. No difference was found between emotional vocalizations and their energy-matched white noises. Despite the phylogenetic gap between Homo sapiens and African monkeys, modern humans and baboons both showed a highly heterogeneous brain process for the perception of vocal and emotional stimuli. The results of this study do not exclude that old evolutionary mechanisms for vocal emotional processing may be shared and inherited from our common ancestor.

How great tits respond to urgency‐based information in allopatric Southern house wren mobbing calls

AbstractMany species of birds use alarm calls to signal information about predators, including the level of threat. Previous playback experiments suggest that the urgency response towards heterospecific calls is phylogenetically conserved, notably in the Paridae family. Using playback experiments conducted on European great tits (Parus major), we tested whether this species perceives information about urgency in mobbing calls produced by an allopatric non‐Paridae species, the Southern house wren (Troglodytes aedon bonariae), by broadcasting calls with high‐calling rate (high threat) and calls with low‐calling rate (low threat). We found that great tits tend to approach the loudspeaker during playbacks of calls with high‐calling rate more often than during playbacks of calls with low‐calling rate. Female great tits gave more calls during playbacks of calls with high‐calling rate than during playbacks of calls with low‐calling rate, whereas there was no significant difference in the number of calls given by males between playbacks of calls with high‐ and low‐calling rates. Thus, our results suggested that great tits perceived the urgency message encoded in calls given by an allopatric non‐Paridae species.

Is the urgency message encoded in heterospecific alarm calls perceived by domestic chickens?

AbstractVertebrate alarm calls can signal danger, and often encode information about predator proximity. Some species of birds alter the number of notes of their alarm calls to reflect urgency, with high‐urgency alarm calls having more notes than low‐urgency calls. Not only do individuals perceive the urgency message encoded in the alarm calls of conspecifics, but also in the alarm calls given by heterospecifics (sympatric and allopatric species). Yet, although well studied in wild species, the capacity to use heterospecific graded alarm call systems has not been investigated in domestic animals. Domestication may have altered the perceptual and communicative abilities of domestic species because they are less threatened by predators. Using playbacks conducted on domestic naked neck chickens (Gallus gallus domesticus) in France, we tested whether this species is able to decode information about urgency in alarm calls produced by a sympatric species; the common chaffinch (Fringilla coelebs), and by an allopatric species; the Australian magpie (Cracticus tibicen). We found the latency to resume foraging behaviour was higher after the high‐urgency call playbacks than the low‐urgency call playbacks, suggesting that the urgency encoded in heterospecific calls was perceived by chickens. However, results seem to indicate that the chickens are not able to discriminate between alarm and control (songs) sounds, but simply respond to specific sound characteristics of each playback stimulus. Our results raise some questions about how animals perceive and attend to information provided by heterospecific alarms. We hope this study will encourage future work with domesticated and nondomesticated animals.

Preferential Begging Responses of Shiny Cowbirds to the Conspecific Chatter Call

Avian brood parasites lay their eggs into the nests of other species, which incubate them and raise the chicks until their independence. Despite living their early weeks of life surrounded by heterospecifics, young brood parasites have the ability to recognize and associate to conspecifics after independence. It has been proposed that the initial conspecific recognition develops when a young parasite encounters a unique species-specific signal that triggers the learning of other aspects of the producer of the signal. For cowbirds (Molothrus spp.), this species-specific signal is hypothesized to be the chatter call. Young birds also could express auditory biases, which in some cases lead to discrimination in favor of conspecific songs. Therefore, the perceptual selectivity for chatters might be also present in nestlings. Our aim was to assess if nestlings of the shiny cowbird (M. bonariensis) present a preferential begging response to conspecific chatter calls. We evaluated if they respond more to the parasitic vocalization than host chicks and if they respond more to the chatter than to heterospecific nonhost calls. We tested shiny cowbird chicks reared by chalk-browed mockingbirds (Mimus saturninus) or house wrens (Troglodytes aedon) and host chicks, as control species. We randomly presented to 6-day-old chicks the following playback treatments: (1) conspecific chatter calls, (2) host calls, used as positive controls, and (3) nonhost calls, used as negative control. We measured if chicks begged during the playback treatments and the begging intensity. When responding to the playback of chatter calls, shiny cowbird chicks begged at a higher frequency and more intensively than host chicks. Shiny cowbird chicks reared by mockingbirds begged more intensively to playbacks of conspecific chatter calls than to host calls, while those reared by wrens begged with a similar intensity to playbacks of conspecific chatter and host calls. On the contrary, wren nestlings begged more intensively to playbacks of the wren call than to chatter calls. Mockingbird nestlings did not beg during any treatment. None of the three species begged during the playback of nonhost calls. Our results show that the chatter call produced a preferential begging response in cowbird nestlings, which may be the beginning of a process of conspecific recognition.

Parent-offspring and inter-offspring responses to conspecific versus heterospecific distress calls in 2 sympatric birds.

Distress calls, as a type of alarm call, play important roles in expressing bodily condition and conveying information concerning predation threats. In this study, we examined the communication via distress calls in parent-offspring and inter-offspring interactions. First, we used playback of chick distress calls of 2 sympatric breeders, the vinous-throated parrotbill Sinosuthora webbiana and the oriental reed warbler Acrocephalus orientalis, to the adults/chicks of these 2 species, respectively, and measured the responses of conspecifics or heterospecifics. The playback-to-chicks experiment showed that both species of chicks reduced the number of begging calls and begging duration time as a response to conspecific/heterospecific distress calls compared with natural begging and background noise controls. However, reed warbler chicks also reduced beak opening frequency in the response to conspecific distress calls compared with other playback stimuli. Second, the results of the playback-to-adults experiment showed that reed warbler adults could eavesdrop on distress calls of conspecific neighbors and sympatric heterospecifics. Furthermore, the nest-leaving behavior of reed warblers did not differ significantly when they heard the distress calls of conspecifics or parrotbills. Finally, reed warbler adults responded to heterospecific distress calls more quickly than to conspecific distress calls, and parrotbill adults presented the same response. Our results supported the warn-kin hypothesis and show that chick distress calls play an important role in conveying risk and the condition of chicks to enhance individual fitness. In addition, we also found that eavesdropping on distress calls is a congenital behavior that begins in the chick stage.

Response to heterospecific calls in non‐passerine species: can two Rallidae species recognise each other based on their vocalisations?

AbstractCommunication is generally assumed to be the domain of conspecific signallers and receivers that produce reliable signals and respond adaptively. However, interactions between coexisting species can be surprisingly complex, suggesting that animals not only perceive but also selectively respond to signals produced by other species. Many species respond to the vocalisations of heterospecifics, but it is usually difficult to separate actual vocal recognition from the response resulting from misidentification. We controlled this bias in a playback experiment with two sympatric Rallidae species, the water rail (Rallus aquaticus) and little crake (Zapornia parva). Both focal species produced more calls and little crake additionally approached the speaker more often in response to calls of each other than to calls of closely related but non‐sympatric spotted crakes (Porzana porzana) or the sympatric but non‐competing little grebes (Tachybaptus ruficollis). By contrast, when responding to each other's calls water rails produced fewer loud calls than during the conspecific treatment suggesting that focal birds were merely announcing their presence, whereas little crakes produced mainly alarms suggesting that they communicated with the mated partner to warn it rather than with the heterospecific intruder. We conclude that focal Rallidae species could distinguish not only their calls from those of conspecifics, but also each other's calls from those of other sympatric and phylogenetically related species.

Diverse patterns of responsiveness to fine temporal features of acoustic signals in a temperate austral forest frog, Batrachyla leptopus (Batrachylidae)

ABSTRACT Phonotactic female and vocal male responses of frogs to advertisement calls have been shown to encompass broader ranges than those of variation of natural mate-attracting signals. Anuran aggressive calls contribute to expand the range of sound features significant for communication. Evoked vocal responses (EVRs) of males of Batrachyla leptopus to synthetic advertisement calls and variants with different temporal features altered parametrically were studied to assess their correspondence with features of natural signals. Frogs responded to stimuli differing in note rate with vocal patterns that depended on the design of the synthetic sounds: lower call rates were obtained with stimuli composed of notes with linear rise-fall times deviating from the average of this parameter for natural calls. However, opposite results were obtained with stimuli composed of sinusoidally amplitude-modulated notes. Calls of longer duration resembling aggressive calls were emitted in response to low note rate sinusoidal stimuli. Stimuli with note durations above and below the natural average, stimuli having low pulse rates and a continuous tone also elicited longer calls of aggressive type. These patterns relate the vocal responses recorded to recognition of conspecific and heterospecific advertisement and aggressive calls, as well as to novel signal features.

The signal value of vocalisations revealing auditory threat assessment in meadow pipit males (Anthus pratensis)

ABSTRACT If territorial males are able to assess the extent of threat posed by con- and heterospecific intruders in an area of sympatry, they could optimise the expression of territorial behaviour. I broadcast recorded vocalisation types of meadow and rock pipit males in the centre of territories to address the following questions: (1) do meadow pipit males respond to conspecific Soft calls, the (’contact’) call emitted by conspecific birds that do not represent a threat to territory or the resident male’s mate; (2) if so, how intensely do they respond to conspecific Soft calls compared with more provocative vocalisations emitted during territorial defence, including the Tsip call elicited by a watching male, or the species-specific part of song (Motif II) – associated with a serious territorial threat; (3) do they discriminate between the homologous Soft calls of meadow and rock pipits? Territorial males responded to conspecific Soft calls as often as to the other two vocalisation types broadcast in territories, but they did not approach the speaker as immediately or as often as to either Tsip or Motif II calls. The latter call elicits a more intense response compared with Tsip. Meadow pipit males discriminate conspecific from heterospecific Soft calls by showing enhanced response to conspecific relative to heterospecific Soft calls.

Simulated chorus attracts conspecific and heterospecific Amazonian explosive breeding frogs

AbstractIn tropical regions, some anuran species breed "explosively", reproducing in massive and highly diverse aggregations during a brief window of time. These aggregations can serve as acoustic beacons, attracting other anurans toward seasonal ponds. We hypothesize that conspecific and heterospecific calls play a role in navigation toward ponds and synchronization of reproduction among species. We simulated a chorus of two species (Trachycephalus coriaceus and Chiasmocleis shudikarensis) with contrasting call characteristics (low‐frequency vs. high‐frequency) and reproductive strategies (strict pond breeder vs. opportunistic) near known explosive breeding sites. We predicted that choruses of T. coriaceus are more attractive to heterospecifics than of C. shudikarensis because the first provides a more reliable indicator of a suitable breeding pond and a better long‐distance signal. We found that both choruses attracted conspecific frogs to the playback outside a natural breeding event. As predicted, heterospecifics were attracted only by low‐frequency calls of T. coriaceus that breeds exclusively in large ponds, but not by higher frequency calls of C. shudikarensis that also breeds in small pools not suitable for other species. Our study presents the first experimental evidence that tropical explosive breeding anurans are attracted to conspecific and heterospecific choruses. The contrasting effect of the playback of the two species on heterospecifics suggests that the attractive effect of a chorus depends on the reproductive strategy of both the sender and the receiver. Given the abundance and diversity of communities in tropical ecosystems, the use of heterospecific acoustic cues may prove widespread and requires further investigation.Abstract in Portuguese is available with online material.

Cross-species effect of separation calls: family dogs’ reactions to pup, baby, kitten and artificial sounds

During separation, infants of various species often produce a special call type, the separation cry, which elicits instant response from the caregiver. Ignoring this stimulus might be costly; hence, adults have evolved a sensitivity to infant cries. As the acoustic structure and function of these vocalizations are conserved across mammals, adults might react similarly to heterospecific and conspecific separation calls. The domestic dog, Canis familiaris, is an excellent model to study reactions to heterospecific vocalizations due to their special niche in the human social environment. Through domestication, they have become especially sensitive to human communicative signals, including baby cries. Furthermore, they can share their natural environment with other species such as other pets and livestock, which could also affect their responsiveness towards heterospecific calls. Taking advantage of this potential cross-species sensitivity, we aimed to examine dogs' reactions to infant separation calls of humans and domestic cats, Felis catus, compared to conspecific calls. To explore the effect of novelty and specific acoustic features we also used synthesized cries, which allowed us to look for general rules behind dogs' reactions to heterospecific calls and general acoustic effects functioning across species. After testing 100 dogs with pup cries in a previous study, here we tested another 118 dogs in three groups based on the presented sounds' origin. All stimuli were analysed acoustically; then we tested the effects of the species and acoustic features on the dogs’ behaviours. Dogs reacted to pup and artificial cries the fastest, and baby cries the slowest, while responses to kitten sounds were intermediate. We also found general acoustic effects: tonality-related parameters extensively affected the reactions. Higher noisiness caused faster speaker and owner orientation, but it seems that species-specific cues might overwrite the general acoustic rules that appear across mammal separation calls.

Female answer specificity to male drumming calls in three closely related species of the stonefly genus Zwicknia (Plecoptera: Capniidae).

This study examines the rate of female answers to conspecific versus heterospecific male vibratory calls in three, closely related stonefly species: Zwicknia bifrons, Z. acuta, and Z. rupprechti. In a previous study those three species were recognized on the basis of their distinct male drumming calls along with differences in genital morphology and genetic divergence. During this study no-choice playback experiments using original male call samples from each species were performed, and the answer rate of females to conspecific and heterospecific signal variants was measured. Mixed effect logistic regression models were used to test if male call species identity had a statistically significant effect on female answer probability. Females answered conspecific male calls with significantly higher probability than heterospecific calls in all the three examined species, suggesting that the divergence of vibrational communication can be an important component of the prezygotic isolation between them. Low, but well detectable responsiveness to heterospecific calls was observable between Z. bifrons and Z. acuta, the two species closest to each other regarding mitochondrial genetic divergence and male call pattern similarity. Thus, our results are most congruent with a tight, gradual coevolution of male calls and female preferences.

Mate Choice Behavior of Female Field Crickets Is Not Affected by Exposure to Heterospecific Calling Songs.

Many animals produce acoustic signals to mark territories and attract mates. When different species produce acoustic signals simultaneously, the signals create a noisy environment, with potential acoustic interference between species. Theoretical studies suggest that such reproductive interference may have strong effects on species interaction. For example, the inferior resource competitor can survive if its disadvantage is counterbalanced by superiority in reproductive interference. Two field cricket species, Teleogryllus occipitalis (Audinet-Serville) (Orthoptera: Gryllidae) and Loxoblemmus equestris Saussure (Orthoptera: Gryllidae), cooccur in the same habitat. A previous study has shown that L. equestris is an inferior species to T. occipitalis in terms of resource competition. Therefore, we predicted that mate location and choice behavior of female T. occipitalis would be negatively affected by the acoustic signals of L. equestris and tested this with a series of playback experiments. The mate choice behavior of female T. occipitalis was not significantly affected by the calling song of L. equestris. Our results suggest that the acoustic interference does not explain the cooccurrence of the two species in the same habitat.

Shared transcriptional responses to con- and heterospecific behavioral antagonists in a wild songbird

The recognition of and differential responses to salient stimuli are among the main drivers of behavioral plasticity, yet, how animals evolve and modulate functional responses to novel classes of antagonistic stimuli remain poorly understood. We studied free-living male red-winged blackbirds (Agelaius phoeniceus) to test whether gene expression responses in blood are distinct or shared between patterns of aggressive behavioral responses directed at simulated conspecific versus heterospecific intruders. In this species, males defend territories against conspecific males and respond aggressively to female brown-headed cowbirds (Molothrus ater), a brood parasite that commonly lays eggs in blackbird nests. Both conspecific songs and parasitic calls elicited aggressive responses from focal subjects and caused a downregulation in genes associated with immune system response, relative to control calls of a second, harmless heterospecific species. In turn, only the conspecific song treatment elicited an increase in singing behavior and an upregulation of genes associated with metabolic processes relative to the two heterospecific calls. Our results suggest that aspects of antagonistic behaviors to both conspecifics and brood parasites can be mediated by similar physiological responses, suggestive of shared molecular and behavioral pathways involved in the recognition and reaction to both evolutionarily old and new enemies.

Great tit responses to the calls of an unfamiliar species suggest conserved perception of call ordering

Many species of birds produce distinct calls when mobbing predators. These calls often recruit nearby conspecifics and heterospecifics to help drive the predators away. In some species, such as members of the family Paridae, mobbing calls are composed of multiple elements that seem to follow a characteristic order. Previous work in parids demonstrated that note ordering influences both the responses of conspecifics and some other co-occurring Paridae species. Cross-species sensitivity to note ordering could result from individuals’ learning to associate individual heterospecific calls with threats or, rather, because the typical note orderings are shared across species. Here, we test these hypotheses by assessing the responses of European great tits (Parus major) to the naturally and artificially ordered calls of black-capped chickadees (Poecile atricapillus), a North American species. In response to the naturally ordered mobbing calls of chickadees, we found that great tits exhibit vigilance and rapidly approach the sound source, behaviors that were indistinguishable to those expressed in response to conspecific calls. If learned associations are necessary for sensitivity to note ordering, then a key prediction is that great tit responses to naturally ordered and artificially reversed chickadee calls should be similar (and weak). In contrast to this prediction, we found that great tits were less vigilant, but approach the sound source in response to artificially reversed chickadee calls. These findings suggest that perception of note ordering patterns is conserved. However, they are also in agreement with a “perception bias” hypothesis: that the first notes of the call mask the notes that follow them, preventing the receiver from perceiving the second part of the call. Although we provide evidence against perception bias, further research is needed to convincingly disentangle these two hypotheses. How do animals decode other species’ vocal sequences? Great tit responses to chickadee sequences depend on the ordering of their notes. Great tits and chickadees never encounter one another in the wild, but their alarm call sequences have similar note orderings. Using a series of playback experiments, we demonstrate that great tits respond strongest to chickadee calls whose order matches their own. Thus, response to unfamiliar calls does not depend on learning, but, rather, shared call ordering across species.

Distress calls of nectarivorous bats (Glossophaga soricina) encode individual and species identity

ABSTRACT Distress calls are known from a variety of animals and are defined as vocalisations emitted during extreme physical stress. Even though distress calls have been studied for a long time, their precise advantage for callers or the significance for receivers is still unclear. In this study, we describe distress calls of the nectarivorous bat Glossophaga soricina (Phyllostomidae: Glossophaginae). Analysing 1925 distress call syllables from 15 individuals caught in the field, we defined six different syllable types. Distress calls were high-intensity, broadband sounds with a low frequency range and thus comparable to those of other taxa. We found statistical evidence for an individual signature in distress calls, but not for a sex-specific signature. Further, playback experiments revealed that group-housed bats responded to distress calls, whereas single-housed bats did not, suggesting that the bats’ response behaviour is influenced by group size. Bats responded significantly to normal and distorted conspecific distress calls but not to heterospecific distress calls. We found no sex-specific differences in the response to different playback stimuli. In conclusion, our results indicate that distress calls of bats encode important social information that can be used by receivers and that the response behaviour of receivers depends on the presence of conspecifics.