The active space of sperm whale codas: inter-click information for intra-unit communication
Description
Publication abstract: Sperm whales (Physeter macrocephalus) are social mega-predators who form stable matrilineal units that often associate within a larger vocal clan. Clan membership is defined by sharing a repertoire of coda types consisting of specific temporal spacings of multi-pulsed clicks. It has been hypothesized that codas communicate membership across socially segregated sympatric clans, while others propose that codas are primarily used for behavioral coordination and social cohesion within a closely spaced social unit. Here, we test these hypotheses by combining measures of ambient noise levels and coda click source levels with models of sound propagation to estimate the active space of coda communication. Coda clicks were localized off the island of Dominica with a four- or five-element 80-meter vertical hydrophone array, allowing us to calculate the median RMS source levels of 1598 clicks from 444 codas to be 161 dB re 1μPa (IQR 153-167), placing codas among the most powerful communication sounds in toothed whales. However, together with measured ambient noise levels, these source levels lead to a median active space of coda communication of about 4 km, reflecting the maximum footprint of a single foraging sperm whale unit. We conclude that while sperm whale codas may contain information about clan affiliation, their moderate active space shows that codas are not used for long range acoustic communication between units and clans, but likely serve to mediate social cohesion and behavioral transitions in intra-unit communication. Data available: The files beginning with "mergedwav" are synched, multi-track acoustic recordings from deployment 1 of our 80 m hydrophone array. The other four deployments used in the above publication are also available upon request, but not included here due to data storage limitations. Recordings were used to calculate the active space of sperm whale codas. The files beginning with "sw" are matlab files containing the tag data from 23 tag deployments on 16 individual sperm whales from the same population. Tag data was used to determine coda production and dive depths.