Repetition patterns in Weddell seal (Leptonychotes weddellii) underwater multiple element calls

Many vocalizations produced by Weddell seals (Leptonychotes weddellii) are made up of repeated individual distinct sounds (elements). Patterning of multiple element calls was examined during the breeding season at Casey and Davis, Antarctica. Element and interval durations were measured from 405 calls all > 3 elements in length. The duration of the calls (22+/-16.6 s) did not seem to vary with an increasing number of elements (F4,404=1.83,p = 0.122) because element and interval durations decreased as the number of elements within a call increased. Underwater vocalizations showed seven distinct timing patterns of increasing, decreasing, or constant element and interval durations throughout the calls. One call type occurred with six rhythm patterns, although the majority exhibited only two rhythms. Some call types also displayed steady frequency changes as they progressed. Weddell seal multiple element calls are rhythmically repeated and thus the durations of the elements and intervals within a call occur in a regular manner. Rhythmical repetition used during vocal communication likely enhances the probability of a call being detected and has important implications for the extent to which the seals can successfully transmit information over long distances and during times of high level background noise.