Within-call repetition may be an anti-masking strategy in underwater calls of harp seals (Pagophilus groenlandicus)

Abstract

Underwater vocalizations of harp seals (Pagophilus groenlandicus) were recorded in the Gulf of St. Lawrence, Canada, during the breeding season in March of 1999 and 2000. At high calling rates (>95 calls/min) the background noise levels increase and individual calls may be masked. The purpose of the study was to determine if seals increase the number of elements per call in response to higher calling rates by conspecifics. Eight multi-element call types were analyzed. Six narrowband and one of two broadband multi-element call types showed a significant increase in the number of elements per call at higher calling rates. One broadband call type did not show a significant difference among the different calling rates. Our findings suggest that harp seals increase the number of elements per call in many call types to avoid having their calls masked by an increasing number of conspecific vocalizations.