P.J.B. Slater

Context-specific use suggests that bottlenose dolphin signature whistles are cohesion calls ☆

Studies on captive bottlenose dolphins, Tursiops truncatus, have shown that each individual produces a stereotyped, individually specific signature whistle; however, no study has demonstrated clear context-dependent usage of these whistles. Thus, the hypothesis that signature whistles are used to maintain group cohesion remains untested. To investigate whether signature whistles are used only in contexts that would require a mechanism to maintain group cohesion, we examined whistle type usage in a group of four captive bottlenose dolphins in two contexts. Individuals were recorded while they were separate from the group and while they all swam in the same pool. Separations occurred spontaneously when one animal swam into another pool. No partitions were used and no aggressive interactions between dolphins preceded separations. Calling animals were identified by an amplitude comparison of the same sound recorded in the two pools. Each dolphin primarily produced one stereotyped signature whistle when it was separated from the group. Similarly the remaining group in the other pool also used primarily their signature whistles if one animal was in a separate pool. If all animals swam in the same pool almost only nonsignature whistles were used. Signature whistle copying was rare and did not initiate reunions or specific vocal responses. The results strongly support the hypothesis that signature whistles are used to maintain group cohesion. Copyright 1998 The Association for the Study of Animal Behaviour.

The different roles of social learning in vocal communication

While vocal learning has been studied extensively in birds and mammals, little effort has been made to define what exactly constitutes vocal learning and to classify the forms that it may take. We present such a theoretical framework for the study of social learning in vocal communication. We define different forms of social learning that affect communication and discuss the required methodology to show each one. We distinguish between contextual and production learning in animal communication. Contextual learning affects the behavioural context or serial position of a signal. It can affect both usage and comprehension. Production learning refers to instances where the signals themselves are modified in form as a result of experience with those of other individuals. Vocal learning is defined as production learning in the vocal domain. It can affect one or more of three systems: the respiratory, phonatory and filter systems. Each involves a different level of control over the sound production apparatus. We hypothesize that contextual learning and respiratory production learning preceded the evolution of phonatory and filter production learning. Each form of learning potentially increases the complexity of a communication system. We also found that unexpected genetic or environmental factors can have considerable effects on vocal behaviour in birds and mammals and are often more likely to cause changes or differences in vocalizations than investigators may assume. Finally, we discuss how production learning is used in innovation and invention, and present important future research questions. Copyright 2000 The Association for the Study of Animal Behaviour.

Song Learning in Zebra Finches (Taeniopygia guttata): Progress and Prospects

Publisher Summary This chapter discusses on the recent findings in song learning in zebra finches and brings them together with earlier studies of song learning in this species, as well as recent physiological work on this species that is relevant to song development. Zebra finch song also affords excellent prospects for further advances in our understanding of principles of behavioral development; the review concludes by considering some of these remaining questions. The chapter summarizes briefly on what is known of the way of life of the zebra finch in the wild, where it occurs in Australia and the Lesser Sunda islands. It is an intensely sociable species, occurring in large flocks and breeding colonially in response to the rainfall, which is essential if there is to be sufficient food for feeding chicks. Zebra finch song seems largely to act as a signal between the sexes, although it is simple in structure and does not therefore fit easily into the scheme of song function. Rather than being concerned primarily with mate attraction or rival repulsion, its major role may be in stimulating ovarian development, including ovulation, a function song is known to possess in other species. This chapter describes what is known about the song-learning system in zebra finches and suggest ways in which the timing, accuracy, and selectivity of learning is affected by the environment that the young bird experiences during its development.

Bird song learning: causes and consequences

This article starts with a brief description of the phenomenon of song learning in birds, and then outlines various consequences that it has for the individuals that show it and the groups to which they belong. Among these are the following features, each of which has been described in at least some species: the sharing of song between kin and between neighbours; changes in song with time; changes with distance, including the phenomenon of dialects. The final section is a discussion of which of these consequences may have functional significance and so be likely to be an advantage of song learning. It is suggested that cultural evolution, geographical variation and dialect boundaries, being features of populations rather than individuals, are epiphenomena without functional significance in themselves. However, song learning may confer advantages stemming from the copying process itself, in interactions with neighbours and in matching song to habitat. The evidence that learnt dialects have a role in assort...

Selective habituation shapes acoustic predator recognition in harbour seals

Predation is a major force in shaping the behaviour of animals, so that precise identification of predators will confer substantial selective advantages on animals that serve as food to others. Because experience with a predator can be lethal, early researchers studying birds suggested that predator recognition does not require learning. However, a predator image that can be modified by learning and experience will be advantageous in situations where cues associated with the predator are highly variable or change over time. In this study, we investigated the response of harbour seals (Phoca vitulina) to the underwater calls of different populations of killer whales (Orcinus orca). We found that the seals responded strongly to the calls of mammal-eating killer whales and unfamiliar fish-eating killer whales but not to the familiar calls of the local fish-eating population. This demonstrates that wild harbour seals are capable of complex acoustic discrimination and that they modify their predator image by selectively habituating to the calls of harmless killer whales. Fear in these animals is therefore focused on local threats by learning and experience.

Minimising Errors in Splitting Behaviour Into Bouts

Some problems in using log survivor functions to split behaviour into bouts are outlined. It is argued that it is usually best to choose that bout criterion which leads to the fewest within and between bout intervals being assigned to the wrong category. A way of doing this is illustrated and other possible criteria are considered. The influence of misassignment on data analysis is discussed and it is argued that where this is substantial analysis in terms of bouts may not be useful.

The vocal behaviour of mammal-eating killer whales: communicating with costly calls

The cost of vocal behaviour is usually expressed in energetic terms; however, many animals may pay additional costs when predators or potential prey eavesdrop on their vocal communication. The northeastern Pacific is home to two distinct ecotypes of killer whales, Orcinus orca, called residents and transients. Resident killer whales feed on fish, a prey with poor hearing abilities, whereas transient killer whales hunt marine mammals, which have sensitive underwater hearing within the frequency range of killer whale vocal communication. In this study, we investigated how the superior hearing ability of mammalian prey has shaped the vocal behaviour of the transient killer whale ecotype. We recorded pulsed calls and the associated behavioural context of groups of transient and resident killer whales in British Columbia and southeastern Alaska. Transient killer whales produced pulsed calls significantly less frequently than residents. Transient killer whales only showed significant amounts of vocal behaviour after a marine mammal kill or when the whales were displaying surface-active behaviour. Vocal activity of transients increased after a successful attack on a marine mammal. Since marine mammals are able to detect killer whale pulsed calls and respond with antipredator behaviour, the reduced vocal activity of transients is probably due to a greater cost for calling in this ecotype resulting from eavesdropping by potential prey. The increase in vocal behaviour after a successful attack may represent food calling (informing other animals in the area about the presence of food), but is more likely to reflect an increase in social interactions during feeding and/or the fact that the cost for vocal behaviour is comparatively low after a successful attack.

Hornbills can distinguish between primate alarm calls.

Some mammals distinguish between and respond appropriately to the alarm calls of other mammal and bird species. However, the ability of birds to distinguish between mammal alarm calls has not been investigated. Diana monkeys (Cercopithecus diana) produce different alarm calls to two predators: crowned eagles (Stephanoaetus coronatus) and leopards (Panthera pardus). Yellow–casqued hornbills (Ceratogymna elata) are vulnerable to predation by crowned eagles but are not preyed on by leopards and might therefore be expected to respond to the Diana monkey eagle alarm call but not to the leopard alarm call. We compared responses of hornbills to playback of eagle shrieks, leopard growls, Diana monkey eagle alarm calls and Diana monkey leopard alarm calls and found that they distinguished appropriately between the two predator vocalizations as well as between the two Diana monkey alarm calls. We discuss possible mechanisms leading to these responses.

Ambient noise, motor fatigue, and serial redundancy in chaffinch song

Many animal signals are performed in a highly redundant manner as in some bird species where males sing several renditions of one song type before switching to another. However, differences in signal redundancy between contexts and between individuals are only poorly understood. We found that chaffinches (Fringilla coelebs) in noisier areas (i.e., close to waterfalls and torrents) sang longer bouts of the same song type before switching to a new type, suggesting that they use increased serial redundancy to get the message across in noisy conditions. This is the first evidence of a noise-dependent adjustment of signal redundancy in a songbird. In addition, we found that song types with faster trills were sung in shorter bouts suggesting that the performance of highly redundant song series is probably limited by motor constraints. Thus, in noisy environments, serial redundancy in bird song may reflect a trade-off between successful signal transmission and preventing motor fatigue.

Cultural Evolution in Chaffinch Song

A detailed study has been made of the song types of male chaffinches in the Orkney Islands. Only about 50 pairs of chaffinches nest there and these are mainly concentrated in three woods, with isolated pairs in a number of other places. Recordings of 41 individuals showed that songs fell clearly into distinct types, 16 of which were discovered. Some song types were peculiar to a single individual, while others occurred in the repertoires of many birds. Most were markedly more common in one wood than in others. The most noticeable variation within a song type was in the number of repetitions of syllables in a phrase. This varied significantly between individuals, though not between different woods; variation within an individual was also great. Comparisons between song types suggested ways in which these had diverged during the course of cultural evolution. The main changes seem to have occurred by minor modification of syllables, by changes in the number of repetitions of syllables, by the addition or omission of sections and by the recombination of sections from different song types. Evidence from the variability and distribution of song types argues against song learning in this species having evolved because it enables individuals to transmit information about their identity or about the locality or kinship group to which they belong. Instead it is suggested that song learning arose as a means of achieving a complex vocal output and that the distribution of song types arises partly because mistakes are sometimes made in copying and partly because some individuals disperse more widely than others after song learning.