Isabelle Charrier

Vocal signature recognition of mothers by fur seal pups

Abstract Subantarctic fur seals, Arctocephalus tropicalis , come ashore to breed in dense colonies and lactating females have to alternate foraging trips at sea with periods ashore during which they suckle their pups. The effectiveness of vocal recognition between mothers and pups, has been shown experimentally. To see whether the recognition abilities of females differ from those of their offspring, we investigated how pups recognize their mothers calls. We used artificially modified signals in playback experiments to determine which acoustic parameters support the recognition process. Pups used both the energy spectrum and the ascending frequency modulation occurring at the beginning of each call. However, they seemed to rely mainly on spectral analyses. The vocal identification process at a perceptual level is therefore asymmetrical, as mothers mainly use temporal structures to recognize their pups calls. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Potential for individual recognition in acoustic signals: a comparative study of two gulls with different nesting patterns

We test relationships between structure of acoustic signal used for individual recognition and nesting ecology among two gulls: the black-headed gull (Larus ridibundus), in which chicks remain in the nest, and the slender-billed gull (L. genei), in which chicks leave the nest after hatching to form crèches. A striking difference between both species is the presence of two fundamental frequencies in the slender-billed gulls call and only one in the black-headed gulls call. Our study shows that the potential for individuality coding is more important in the species where the offspring experiment the greatest constraints--due to their nesting pattern--to identify their parents.

Vocal recognition of mothers by Australian sea lion pups: individual signature and environmental constraints

As in all otariids, Australian sea lion, Neophoca cinerea, females alternate foraging trips at sea with suckling periods ashore, and each time they return, mothers and pups have to find each other among individuals at the colony. The need for a finely tuned mechanism of individual recognition is exacerbated by their habit of changing the suckling location. Using playback experiments with modified calls, we investigated the acoustic parameters involved in the discrimination of the mother by pups. The signature efficiency was also tested in the three environments in which reunions at the study site occur by performing propagation tests. Pups paid great attention to both amplitude and frequency modulations, and to the exact frequency values of the call to identify their mother. When severe modifications of AM and FM patterns were made to mothers’ calls pups no longer responded to them. This may have arisen because the calls fell outside the natural species range. The energy spectrum, even though highly individualized, was not important for individual recognition. Propagation tests revealed that one particular environment was extremely harsh and did not allow accurate transfer of the individual signature components whatever the distance. In two other environments, AM was only reliable to a distance of 16 m, but both FM and frequency spectrum could be transmitted with limited degradation over 32 m. The different environments greatly influenced the efficiency of the individual identification process. Accordingly, the area in which mother–pup reunions occur is an important factor in the success of individual recognition.

INDIVIDUAL VOCAL IDENTITY IN MOTHER AND PUP AUSTRALIAN SEA LIONS (NEOPHOCA CINEREA)

Abstract Individual vocal recognition between mothers and pups has been widely observed in pinnipeds, especially otariids. Otariids are colonial breeders; mothers suckle only their own offspring, aggressively attacking nonrelated young. Mothers alternate foraging trips with periods ashore, and at each return to the colony, mothers and pups must find each other among all the individuals of the colony. In the Australian sea lion (Neophoca cinerea), the need for a finely tuned mechanism of recognition is exacerbated by their habit of changing the nursing location over the course of lactation. We investigated potential acoustic parameters used in mother–pup recognition in Australian sea lions. We measured 11 acoustic parameters on calls of mothers and pups and found that several parameters (fundamental frequency, energy spectrum, amplitude, and frequency modulation) were highly individually specific. Discriminant analysis correctly assigned calls to individual mothers or pups with an average classification rate of 65% and 77%, respectively. Spectral features and frequency modulation were the most important features distinguishing individuals. Lastly, principal component analysis showed that calls of pups and mothers were easily distinguishable using energy spectrum and frequency modulation. Comparison with other pinniped species suggests that individual vocal identity is likely to be selected through ecological constraints such as density of the colony, degree of polygyny, likelihood of allosuckling or fostering, and degree of maternal absence during lactation.

Social olfaction in marine mammals: wild female Australian sea lions can identify their pup's scent

Historically, anatomical evidence has suggested that marine mammals are anosmic or at best microsmatic, i.e. absent or reduced olfactory capabilities. However, these neuroanatomical considerations may not be appropriate predictors for the use of olfaction in social interactions. Observations suggest that pinnipeds may use olfaction in mother–pup interactions, accepting or rejecting pups after naso-nasal contact. Such maternal–offspring recognition is a favourable area for investigating the involvement of odours in social recognition and selectivity, as females are evolutionarily constrained to direct resources to filial young. However, there is no experimental, morphological or chemical evidence to date for the use of olfaction in social contexts and for individual odour recognition abilities in pinnipeds. Here, we report unequivocal evidence that Australian sea lion (Neophoca cinerea) females can differentiate between the odour of their own pup and that of another, in the absence of any other distinguishing cues. This study demonstrates individual olfactory recognition in a free-ranging wild mammal and is clear evidence of the social function of olfaction in a marine mammal.

Individual identity encoding and environmental constraints in vocal recognition of pups by Australian sea lion mothers

Colonial living imposes strong selection pressures on the communication systems of species with many animals communicating on the same sensory channels simultaneously. Colonial species often exhibit complex individual vocal signatures that encode a caller’s identity in their vocalizations. During lactation, Australian sea lion, Neophoca cinerea, mothers and pups are repeatedly separated when mothers leave the colony to forage. After maternal foraging trips, mothers and pups must reunite in the colony. Both mothers and pups produce individually distinctive vocalizations during reunions and can recognize their counterpart’s calls. Using playback experiments with modified calls, we investigated the acoustic parameters involved in the recognition of pup vocalizations by mothers. We also examined the efficiency of the vocal signature in three habitat types within the colony using propagation tests. We found that Australian sea lion females used a combination of temporal, amplitude and frequency parameters to recognize their pup’s vocalizations. Pup vocalizations were severely degraded in the herbaceous dune habitat type with no vocal signature components reliably propagating to any measured distance. By contrast, calls propagated comparatively well in the shrubby dune habitat of the colony, as the vegetation appeared to act as a windshield. This study shows that the vocal signatures of Australian sea lion pups are both shaped and constrained by their environment and ecology, and that these signatures are of a moderate level of complexity when compared to those of other colonial vertebrates.

Vocal identity and species recognition in male Australian sea lions, Neophoca cinerea

SUMMARY The acoustic channel is important for communication in otariids (fur seals and sea lions). Discrimination between species, sex or individuals is essential in communication; therefore insight into the role of vocalisations in recognition is vital to understanding otariid social interactions. We measured vocalisations and their use in discriminating sex and species in male Australian sea lions (Neophoca cinerea). Barking calls of mature males were recorded and analysed based on five acoustic parameters. A discriminant function analysis classified calls to the correct individual at a classification rate of 56%, suggesting that male barking calls are individually distinctive with the potential to facilitate individual vocal recognition. Playback experiments were used to assess the role of vocalisations in sex and species recognition both in and out of the breeding season. Males showed significantly stronger reactions to both conspecific and heterospecific males than they did to conspecific females and were most responsive during the breeding season. Australian sea lion males have the most depauperate vocal repertoire of any otariid. This simple repertoire may reflect the ecological circumstances in which these animals breed, with very low colony densities, asynchronous breeding and low levels of polygyny. Yet even in this simple system, males are able to discriminate between males and females of their own species, and distinguish the calls of conspecifics from other species. The barking calls of male Australian sea lions have sufficient information embedded to provide the potential for individual discrimination and this ability will be assessed in future studies.

What makes an Australian Sea Lion (Neophoca cinerea) male's bark threatening?

In mammals, vocal signals are produced in many social contexts and convey diverse information about the emitter (social rank, individual identity, body size-condition). To understand their biological function, the authors find it is not only important to estimate the information about the signaler encoded in the signal but also to determine if and how this information is perceived by the receiver. In male pinnipeds (phocids, otariids, and odobenids) vocal signaling plays an important role in the breeding season during the defense of territories, females, or both. In this article, the authors investigated 2 key acoustic features that Australian sea lion (Neophoca cinerea) males most likely rely on to assess the threat level posed by potential rivals, by manipulating bark rhythmicity and spectral characteristics. Bark series that show accelerated rhythmicity and higher formants elicited stronger responses.

Statistical Classification of Black-Capped (Poecile Atricapillus) and Mountain Chickadee (Poecile Gambeli) Call Notes

Both black-capped (Poecile atricapillus) and mountain chickadees (Poecile gambeli) produce a chick-a-dee call that consists of several distinct note types. In some regions, these 2 species live sympatrically, and it has been shown that 1 species will respond weakly to songs of the other. This suggests that chickadee song, and potentially other of their vocalizations, contains species-specific information. We tested the possibility that call notes were acoustically sufficient for species identification. Black-capped and mountain non-D notes were summarized as a set of 9 features and then analyzed by linear discriminant analysis. Linear discriminant analysis was able to use these notes to identify species with 100% accuracy. We repeated this approach, but with black-capped and mountain D notes that were summarized as a set of 4 features. Linear discriminant analysis was able to use these notes to identify species with 94% accuracy. This demonstrates that any of the note types in these chickadee calls possesses sufficient information for species classification.

Acoustic features involved in the neighbour-stranger vocal recognition process in male Australian fur seals

Many territorial species have the ability to recognise neighbours from stranger individuals. If the neighbouring individual is assumed to pose less of a threat, the territorial individual responds less and avoids unnecessary confrontations with familiar individuals at established boundaries, thus avoiding the costly energy expenditure associated with fighting. Territorial male Australian fur seals respond more to strangers than to neighbouring males. The present study evaluated which acoustic features were important in the neighbour-stranger recognition process in male Australian fur seals. The results reveal that there was an increase in response strength or intensity from males when they heard more bark units, indicating the importance of repetition to detect a caller. However, lengthening and shortening the inter-unit spaces, (i.e. changing the rhythm of the call) did not appear to significantly affect an animals response. In addition, the whole frequency spectrum was considered important to recognition with results suggesting that they may vary in their importance. A call containing the dominant and surrounding harmonics was considered important to a males ability to recognise its neighbour. Furthermore, recognition occurs even with a partial bark, but males need to hear between 25 and 75% of each bark unit from neighbouring seals. Our study highlights which acoustic features induce stronger or weaker responses from territorial males, decoding the important features in neighbour-stranger recognition.