Diel patterns in underwater sounds by Weddell seals during two breeding seasons

Abstract

Automated underwater recordings of Weddell seal (Leptonychotes weddellii) vocalizations were made continuously once per hour for 2.5 min during the austral breeding season. Recordings were made during two breeding seasons: October 1976 through December 1976 and October 1977 through January 1978 at Hutton Cliffs, Antarctica. From radio‐telemetry studies this species is known to exhibit a diel pattern in haulout on the ice. From census studies of tagged seals it is known they exhibit seasonal fluctuations in the number of seals hauled out on the ice. We studied how variations in the rate of different underwater call types reflected the haulout pattern and the changes in the colony associated with territorial defense, underwater breeding, and dispersal from the colony. The 34‐call repertoire was evaluated for hourly, weekly, and annual variations in usage. The trill vocalization and the serial chug vocalization had the most significant variation for both the weekly and hourly analysis. The trill call type is thought to be important in mate attraction by underwater territorial males. The chug call is thought to be important in aggressive encounters between males. An increase rate of these call types might be a useful predictor of the onset of the mating period.