The vocal behaviour of the grey seal (Halichoerus grypus)

Abstract

This thesis is an observational and experimental study of the vocal behaviour in the grey seal (Halichoerus grypus). It provides the first comprehensive description of in-air and underwater vocalisations for the eastern Atlantic population of grey seals and compares it to the western Atlantic population. Two out of 6 in-air call types were very similar to underwater vocalisations and of the 10 eastern Atlantic underwater vocalisations 5 were comparable to the western Atlantic repertoire described earlier. Most calls were found to occur on their own, while some were preferentially associated in time with other call types. In addition, the number of particular types of underwater vocalisation did not display any diurnal variation, but did vary' across the breeding season. Experimental studies were also carried out on the role of pup vocalisations in mother-pup vocal recognition at two reproductively isolated colonies: the Isle of May, Scotland and Sable Island, Nova Scotia, Canada. Pup vocalisations were found to be both stereotyped and individually distinctive, features normally associated with a system of individual recognition. Allo-suckling was observed to be widespread on the Isle of May but was absent on Sable Island. Playback experiments revealed that mothers on the Isle of May did not respond more to vocalisations of their own pup than to those of non-filial pups. In contrast, on Sable Island, mothers were able to discriminate between their own and other pup calls. This suggests that different selective pressures may be affecting the two colonies, and possible reasons are discussed.