Sequential calls and associated behavior in captive bearded seals (Erignathus barbatus)

Bearded seals produce complex underwater sounds suggested to function as territorial and/or courtship signals. However, little is known about behavioral context of the vocalization, mainly because direct observation is difficult in the wild. In this study, we recorded underwater sounds and behaviors of three captive bearded seals (an adult male and two adult females) in Otaru aquarium, Japan, between March 2012 and April 2016, in order to identify the caller and to record association between vocalization and behaviors. The male continuously vocalized from December until April with a peak in March, equivalent to breeding season in the wild. In contrast, the females vocalized only 1-2 weeks in March or April. The male and the females produced 3 and 5 call types, respectively, sharing 2 call types. The 3 call types of the male occurred in a regularly ordered sequence that was stable during this study. The females responded to the male sequential calls by nuzzling against the throat of vocalizing male during the breeding season, when the females also actively vocalized. Our results suggest that underwater vocalization of bearded seals might be used as a courtship signal between male and female possibly to advertise their reproductive status.