Summary
Underwater vocalization monitoring and surveys, both on ice and underwater were used to determine if Weddell seals( Leptonychotews eddellit)n ear Mawson Station, Antarctica, remain under the fast ice during winter within close range of breeding sites. Daytime and nighttime underwater calling rates were examined at seven breeding sites during austral winter and spring to identify seasonal and diel patterns. Seals rarely hauled out at any of the sites during winter, although all cohorts (adult males, females, and juveniles) were observed underwater and surfacing at breathing holes throughout winter (June-September) and spring (October-December). Seal vocalizations were recorded during each sampling session throughout the stUdy (n = 102 daytime at seven sites collectively, and n = 5 24-h samples at each of two sites). Mean daytime calling rate was low in mid-winter (July) (mean = 18.9 :i: 7.1 calls/min) but increased montWy, reaching a peak during the breeding season (November) (mean = 62.6:i: 15.7 calls/min). Mean nighttime calling rate was high throughout the winter and early spring (July-October) with mean noctUrnal calling rate in July (mean = 61.8 :i: 35.1 calls/min) nearly equal to mean daytime calling rate in November (during 24-h daylight). Reduced vocal behavior during winter daylight periods may result from animals utilizing the limited daylight hours for nonvocal activities, possibly feeding.