Clear diel patterns in breeding calls of harbor seals (Phoca vitulina) at Hornby Island, British Columbia, Canada

Abstract

During the breeding season, male harbor seals (Phoca vitulina Linnaeus, 1758) produce underwater calls for sexual advertisement. The daily and seasonal timing of these calls is influenced by female availability (i.e., tidal haul-out patterns, foraging behavior, and oestrus cycle). Therefore, temporal patterns of male calling can provide clues about patterns of female behavior. We collected underwater recordings during the 2014 breeding season at Hornby Island, British Columbia, Canada, and examined the relationships of light level, progression of breeding season, and tide relative to call presence or absence and calling rate. Calls were 15 times more likely to occur at night than during the day. Nocturnal peaks in calling rate have been observed in other harbor seal populations and have been attributed to tidal haul-out patterns and nocturnal foraging of females. In this study, tide level did not have a significant effect on calling rate, and female foraging behavior was not monitored. One acoustic observation of mammal-eating killer whale (Orcinus orca (Linnaeus, 1758)) calls was followed by 48 h of decreased calling rate. We infer that predation risk influences the temporal pattern of male calling at this location and suggest further study to support this hypothesis.