BIOACOUSTICS OF DOMESTICATION: ALARM AND COURTSHIP CALLS OF WILD AND DOMESTIC CAVIES

ABSTRACT

Comparisons of wild (Cavia aperea) and domestic (C. porcellus) cavies promote an understanding of the physiological and behavioral effects of domestication. The richness and peculiarities of Cavia acoustic repertoires encourage the use of this model for testing how domestication alters repertoires and the physical structure of calls. We present a comparison between alarm and courtship calls of domestic and two populations of wild cavies from different geographic regions, one of them with a short-term captivity history of 25 generations. We found significant differences between domestic and wild cavies in both calls, particularly in temporal parameters, and only spectral differences between two wild populations in alarm calls. There were also differences in the frequency of emission of calls: alarm calls were more frequent in the wild and courtship calls were more frequent in the domestic species. Our results suggest that domestication has influenced the temporal parameters of both alarm and courtship calls of C. porcellus, but not the spectral parameters that, instead, may be influenced by environment or population factors.     

Male blue monkeys alarm call in response to danger experienced by others

Male blue monkeys (Cercopithecus mitis stuhlmanni) of Budongo Forest, Uganda, produce two acoustically distinct alarm calls: hacks to crowned eagles (Stephanoaetus coronatus) and pyows to leopards (Panthera pardus) and a range of other disturbances. In playback experiments, males responded to leopard growls exclusively with a series of pyows and to eagle shrieks predominantly with hacks. Responses to playbacks of these alarm call series matched the responses to the corresponding predators, suggesting that the calls conveyed something about the nature of the threat. When responding to a series of hacks, indicating an eagle, males responded predominately with hacks, but produced significantly more calls if their group members were close to the playback stimulus than far away, regardless of their own position. When responding to a series of pyows, indicating a range of disturbances, males responded with pyows, but call rates were independent of the distance of other group members. The results suggest that males took into account the degree of danger experienced by other group members.     

No evidence of eavesdropping on heterospecific alarm calls by captive zebra finches recently descended from wild birds

Alarm calls are vocalisations animals give in response to predators which mainly function to alert conspecifics of danger. Studies show that numerous species eavesdrop on heterospecific calls to gain information about predator presence. Responding to heterospecific calls may be a learned or innate response, determined by whether the response occurs with or without prior exposure to the call. In this study, we investigated the presence of eavesdropping behaviour in zebra finches Taeniopygia guttata. This species is not known to possess a distinct alarm call to warn adult conspecifics of a threat, and could be relying on alarm calls of nearby heterospecifics for predator information. We used a playback experiment to expose captive zebra finches to three heterospecific sounds: an unfamiliar alarm call (from the chestnut‐rumped thornbill Acanthiza uropygialis), a familiar alarm call, and a familiar control (both from the noisy miner Manorina melanocephala). These calls were chosen to test if the birds had learnt to distinguish between the function of the two familiar calls, and if the acoustic properties of the unfamiliar alarm indicated presence of a threat to the finches. Our results showed that in response to the thornbill alarm, the birds reduced the rate of production of short calls. However, this decrease was also seen when considering both short and distance calls in response to the control sound. An increase in latency to call was also seen after the control stimulus when compared to the miner alarm. The time spent scanning increased in response to all three stimuli, but this did not differ between stimuli. There were no significant differences when considering the stimulus by time interaction for any of the three vigilance measures. Overall, no strong evidence was found to indicate that the captive zebra finches were responding to the heterospecific alarm stimuli with anti‐predator behaviour.     

Experimental study of alarm calls of the oriental tit (Parus minor) toward different predators and reactions they induce in nestlings

Anti-predatory strategies of birds are diverse and may include predator-specific alarm calls. For example, oriental tit (Parus minor) parents can distinguish snakes from other predators and produce snake-specific referential vocalizations ("jar" call) when a snake poses a threat to their nest. The “jar” call has a very specific function to induce fledging of nestlings close to fledging age. This reaction ensures nestlings' survival in natural encounters with snakes that are capable of entering nest cavities and kill entire broods. Sciurid rodents, like chipmunks, may pose a similar threat to cavity-nesting birds. We explored the hypothesis that parents use the fledging-inducing alarm vocalizations in this situation, because chipmunks, like snakes, can kill the brood upon entering the nest cavity. We compared alarm calls of parents toward two predators (chipmunk and snake) who pose a similar threat to the nestlings in a nest cavity, and toward an avian predator (Eurasian jay) who cannot enter nest cavities and poses no threat to the nestlings in a nest. Our results show that the vocal responses of oriental tits were different among the three predators. This suggests that the acoustic properties of vocal responses to predators are different between predators of a similar hunting strategy (nest-cavity entering). The playback of recorded vocal responses of parents to chipmunks did not trigger the fledging of old nestlings, whereas the vocalizations toward a snake did, as shown by earlier studies. Our study suggests that the vocal response of parents does not carry information about the ability of predators to enter the nest cavity and confirms the special status of alarm calls triggered by snakes.     

Psycholinguistic analyses of alarm calls of Japanese monkeys (Macaca fuscata fuscata)

Alarm and estrous calls emitted by Japanese macaques were recorded and analyzed in the Arashiyama West and East groups. Their responses to natural calls as well as to synthesized versions varying in the acoustic parameters that defined the vocalizations were studied. The response patterns shown by Arashiyama West group members, which were subject to a distinct change with only a slight difference of a single parameter, appeared to reflect strict underlying perceptual boundaries. This was analogous to the categorical perception that humans show with speech sounds. In contrast, continuous perception was exhibited by Arashiyama East group individuals. When several sounds were played back in combination to the former group, following stimuli were recognized by quite different cues from those by which the first sound was perceived. The groups' differences in vocal perception are discussed in terms of the ecological differences of the environments they inhabit.     

Flights of fear: a mechanical wing whistle sounds the alarm in a flocking bird

Animals often form groups to increase collective vigilance and allow early detection of predators, but this benefit of sociality relies on rapid transfer of information. Among birds, alarm calls are not present in all species, while other proposed mechanisms of information transfer are inefficient. We tested whether wing sounds can encode reliable information on danger. Individuals taking off in alarm fly more quickly or ascend more steeply, so may produce different sounds in alarmed than in routine flight, which then act as reliable cues of alarm, or honest ‘index’ signals in which a signal''s meaning is associated with its method of production. We show that crested pigeons, Ocyphaps lophotes, which have modified flight feathers, produce distinct wing ‘whistles’ in alarmed flight, and that individuals take off in alarm only after playback of alarmed whistles. Furthermore, amplitude-manipulated playbacks showed that response depends on whistle structure, such as tempo, not simply amplitude. We believe this is the first demonstration that flight noise can send information about alarm, and suggest that take-off noise could provide a cue of alarm in many flocking species, with feather modification evolving specifically to signal alarm in some. Similar reliable cues or index signals could occur in other animals.     

Fork-tailed drongos use deceptive mimicked alarm calls to steal food

Despite the prevalence of vocal mimicry in animals, few functions for this behaviour have been shown. I propose a novel hypothesis that false mimicked alarm calls could be used deceptively to scare other species and steal their food. Studies have previously suggested that animals use their own species-specific alarm calls to steal food. However none have shown conclusively that these false alarms are deceptive, or that mimicked alarm calls are used in this manner. Here, I show that wild fork-tailed drongos (Dicrurus adsimilis) make both drongo-specific and mimicked false alarm calls when watching target species handling food, in response to which targets flee to cover abandoning their food. The drongo-specific and mimicked calls made in false alarms were structurally indistinguishable from calls made during true alarms at predators by drongos and other species. Furthermore, I demonstrate by playback experiments that two of these species, meerkats (Suricata suricatta) and pied babblers (Turdoides bicolor), are deceived by both drongo-specific and mimicked false alarm calls. These results provide the first conclusive evidence that false alarm calls are deceptive and demonstrate a novel function for vocal mimicry. This work also provides valuable insight into the benefits of deploying variable mimetic signals in deceptive communication.