Further studies of the role of harbour seal (Phoca vitulina) pup vocalizations in preventing separation of mother–pup pairs

Abstract

Calls of harbour seal (Phoca vitulina) pups, propagated simultaneously in air and underwater while the pups' heads were above the surface of the water, were recorded to examine in detail the differences between them and to determine if both versions are individually distinct. Although the airborne and underwater versions of the calls were different from one another, they were distinct for each pup on the basis of several physical parameters, primarily the frequency of the major harmonic. Interactions between the mothers and pups at the time of calling were observed to assess the role of the cries in maintaining mother–pup contact. Analysis of the variations in vocalizations and contextual data supported the hypothesis that the mothers use these vocalizations for individual recognition of their offspring and for ensuring that contact with them is maintained. It is postulated that differences between the aerial and underwater versions of calls increase the accuracy with which the mothers can locate their pups.

Acoustic Structure and Individual Variation of Grey Seal (Halichoerus Grypus) Pup Calls

“…Individual differences appear for all the acoustic features we studied but a higher level of individuality is observed in fundamental frequency, the number of harmonics and the location of peak energy. In Phoca vitulina pup calls, Perry & Renouf (1988) stressed the importance of fundamental frequency as an individual characteristic, but our results do not indicate that one feature alone accounts for the major part of individual variation.…”

“…For some species (Mirounga angustirostris, Petrinovich, 1974; Arctocephalus galapagoensis and Zalophus californianus, Trillmich, 1981;Phoca vitulina, Renouf, 1985; Arctocephalus tropicalis, Roux & Jouventin, 1987), the mother's reaction to vocalizations of her own offspring was compared with the reaction to unknown pup calls through playback experiments and successful discrimination by females was confirmed. In Callorhinus ursinus (Takemura et al, 1983;Insley, 1992), Arctocephalus tropicalis (Roux & Jouventin, 1987), P. vitulina (Perry & Renouf, 1988) and M. angustirostris (Insley, 1992), variability in the acoustic structure of pup calls was considered to offer a sufficient basis for individual identification. The ability of a female to recognize her pup through vocalizations may be particularly important in species with long lactation periods during which mother-pup separation occurs regularly and in species that breed in dense aggregations (Bowen, 1991;Insley, 1992).…”

Mother–pup vocal recognition in harbour seals: influence of maternal behaviour, pup voice and habitat sound properties

“…no background noise, no overlap with vocalizations from other animals) were selected for use as playback stimuli during the subsequent capture of the pup. In natural contexts, harbour seal pup vocalizations differ according to the level of stress faced by the pup (Perry & Renouf, 1988). It is likely that calls from the present study were typical of stressed pups since they were recorded while animals were captured.…”

“…During each session, a stimulus was broadcast from the boat and the female's behavioural response was noted during the following 90 s. An additional 90 s interval allowed the female to return to her initial motivational state before the second stimulus was broadcast and the behavioural response noted for another 90 s. Treatment order (calls from own or nonfilial pup broadcast first) was randomized. Stimuli were broadcast simultaneously in air and underwater to mimic natural pup calling behaviour since calls produced when pups are at the water's surface propagate in both media (Perry & Renouf, 1988;Renouf, 1984;Sauv e et al, in press). Stimuli were broadcast using a MP3 player (Edirol R-09 WAVE/MP3 Recorder, Roland Corporation U.S., Los Angeles, CA, U.S.A.) connected to both a portable loudspeaker (frequency response: 70 Hz e 15 kHz; Permio 8, TAG, Saint Jean de V edas, France) held above the surface of the water (<50 cm) and an underwater speaker (frequency response: 200 Hz e 20 kHz; LL916, Lubell Labs, Columbus, OH, U.S.A.) placed at a minimum depth of 1 m. Amplitudes of playback stimuli were adjusted to 92e94 dB SPL (re.…”

“…Females therefore perceive and use individual vocal markers previously identified in harbour seal pup calls (Khan, Markowitz, & McCowan, 2006;Perry & Renouf, 1988;Renouf, 1984;Sauv e et al, in press) for individual vocal recognition.…”