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PhD Candidate, Macquarie University


The role of different sensory cues in the recognition process of sea lion pups by their mothers

Recognition plays an important role in communication systems in many animals. While it is known that a majority of recognition utilises multiple sensory modalities for conveying information, the understanding of the roles that different sensory cues play in the recognition process is poor. The ability of fur seal and sea lion females to locate and identify their own offspring on return to the colony after foraging trips is critical to pup survival. Acoustic, visual and olfactory cues are all used by females when searching for and identifying their pups, yet there is a dearth of information about the relative importance of these cues during mother-pup reunions. I conducted a series of experiments in a wild population of Australian sea lions (Neophoca cinerea) in which I aimed to 1) determine how simultaneous presentation of multiple cues influences the behavioural response of mothers, and 2) assess the relative importance of acoustic and olfactory cues. I found that presenting multiple cues resulted in an increase in the females’ investigatory behaviour, but not the number of produced calls. The identity (filial/non-filial) of the acoustic cues did not influence the number of investigations. However, a stronger vocal response occurred when filial acoustic cues were played, compared to treatments with non-filial acoustic cues. My results demonstrated a cross-modal effect of cues - the ability to prompt the behavioural response of a different sensory channel. I showed that despite each sensory cue accurately conveying similar information when presented in isolation, if combined, their function and relative influence on specific behavioural responses are different. The results of this study give new insight into the importance of multimodal studies and the underlying processes of multimodal recognition and will contribute to understanding how different communication systems evolved.


When were the weaners weaned? Identifying the onset of Australian sea lion nutritional independence

Abstract: Weaning in mammals is typically thought of as the transition from reliance on maternal milk to feeding independently. Current theory suggests a complex process involving mothers imparting enough resources to offspring as to ensure survival without compromising both prior and future reproductive efforts, and the demands of offspring whose primary concern is survival. Otariid seals are a suitable group to study this given the morphological and behavioral similarities across species of the primary care giver, adult females. At higher latitudes, the duration of maternal care is short and tightly linked to seasonal productivity of the marine environment, punctuated by a predictable migration of mothers away from breeding sites. In contrast, nonmigratory temperate latitude otariid species have a much wider range of lactation periods, with mothers prolonging maternal support in relation to seasonal unpredictability of food resource. Prolonging care into the subsequent reproductive effort will likely have profound effects on the survival of the younger offspring. The Australian sea lion Neophoca cinerea has broken the phylogenetic constraint of a 12-month breeding cycle, which may reflect an alternate strategy to reduce the fitness costs of prolonged support by providing up to 18 months nutritional support to offspring. We use stable isotope analysis of temporally matched whisker sections combined with telemetry data on nutritionally dependent Australian sea lion pups to determine the weaning process and characterize the transition to nutritional independence. Using changes in isotopic nitrogen (15N) over time, pups undergo a gradual transition to independent foraging during a 3- to 6-month period before the onset of the next reproductive effort. Telemetry data supported this conclusion, indicating benthic foraging of weaned pups in areas consistent with adult female foraging.

Pub.: 27 Sep '16, Pinned: 16 Jun '17

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

Abstract: 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.

Pub.: 01 Jul '08, Pinned: 16 Jun '17

Rapid onset of maternal vocal recognition in a colonially breeding mammal, the Australian sea lion.

Abstract: In many gregarious mammals, mothers and offspring have developed the abilities to recognise each other using acoustic signals. Such capacity may develop at different rates after birth/parturition, varying between species and between the participants, i.e., mothers and young. Differences in selective pressures between species, and between mothers and offspring, are likely to drive the timing of the onset of mother-young recognition. We tested the ability of Australian sea lion mothers to identify their offspring by vocalisation, and examined the onset of this behaviour in these females. We hypothesise that a rapid onset of recognition may reflect an adaptation to a colonial lifestyle.In a playback study maternal responses to own pup and non-filial vocalisations were compared at 12, 24 and every subsequent 24 hours until the females' first departure post-partum. Mothers showed a clear ability to recognise their pup's voice by 48 hours of age. At 24 hours mothers called more, at 48 hours they called sooner and at 72 hours they looked sooner in response to their own pup's vocalisations compared to those of non-filial pups.We demonstrate that Australian sea lion females can vocally identify offspring within two days of birth and before mothers leave to forage post-partum. We suggest that this rapid onset is a result of selection pressures imposed by a colonial lifestyle and may be seen in other colonial vertebrates. This is the first demonstration of the timing of the onset of maternal vocal recognition in a pinniped species.

Pub.: 24 Aug '10, Pinned: 16 Jun '17