The acoustic repertoire of hooded seals (Cystophora cristata)

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Abstract
Airborne and waterborne acoustic sounds of hooded seals (Cystophora cristata) were recorded during the breeding seasons of 1988 and 1989 in the Gulf of St. Lawrence, Canada. During 36 h of in-air focal-animal sampling and 9 h of ad libitum underwater sampling, 410 sounds, in total, were recorded and analyzed. In the field, the context of signals was noted whenever possible. This included the behaviour of the signaller and that of its nearest neighbour. Frequency and temporal variables, measured directly from sonograms, were analyzed using a combination of principal components analysis and cluster analysis. Three major classes of sounds containing 5 call types were suggested by the cluster analysis. Variation occurs in the structure of calls both within and between call classes. Sounds that were created using the hood and septum both under water and in air, as well as a variety of underwater clicks and knocks, were distinct from voiced, airborne calls. Not surprisingly, most acoustic signals were used in agonistic (79%) or sexual (12%) situations during the reproductive period.