Underwater call sequences of Weddell seals (Leptonychotes weddellii) at the Vestfold Hills, Antarctica

摘要

Repeated sequences of different call types have been reported in some recordings of underwater calls of Weddell seals (Leptonychotes weddellii) but not others. Recordings made during the breeding seasons of 1990 (1 site, n = 1,136 calls), 1991 and 1992 at three and seven sites, respectively (n < 210 calls per study site) at the Vestfold Hills, Antarctica, were examined. Calls were classified into 16 types, and series of calls were examined for two data sets (1990) and for all years. The low number of seals at these breeding sites resulted in a long series of calls with no overlap, thus facilitating the opportunity for sequence analyses. At most, but not all, study sites there was a three-call-sequence that occurred above chance levels. Thirty-five of 43 three-call-sequences were only detected in one year at one recording location; the other eight were heard at up to four study sites in the same year. Five sets of three-call-sequences occurred in the reverse order of other sequences. Pairs of calls were common, and most occurred in one order and not the reverse. During 3 h of observations of a male-female pair of Weddell seals lying quietly in a pool, there were no sequences of calls or dueting (n = 241 calls). Our findings support the hypothesis that some Weddell seals make nonrandom series of calls, but the functional significance of these patterns is uncertain. Because similar sequences occurred at several study sites, however, it is not likely that call sequences could be used as a natural acoustic tag to identify individual seals.