Time patterns of sperm whale codas recorded in the Mediterranean Sea 1985-1996

A distinctive vocalization of the sperm whale, Physeter macrocephalus (=P. catodon), is the coda: a short click sequence with a distinctive stereotype d time pattern [Watkins and Schevill, J. Acoust, Sec. Am. 62, 1485-1490 (19 77)]. Coda repertoires have been found to vary both geographically and with group affiliation [Weilgart and Whitehead, Behav. Ecol. Sociobiol. 40, 277 -285 (1997)]. In this work, the click timings and repetition patterns of sp erm whale codas recorded in the Mediterranean Sea are characterized statist ically, and the context in which the codas occurred are also taken into con sideration. A total of 138 codas were recorded in the central Mediterranean in the years 1985-1996 by several research groups using a number of differ ent detection instruments, including stationary and towed hydrophones, sono buoys and passive sonars. Nearly all (134) of the recorded codas share the same "3+1" (/// /) click pattern. Coda durations ranged from 456 to 1280 ms , with an average duration of 908 ms and a standard deviation of 176 ms. Mo st of the codas (a total of 117) belonged to 20 coda series. Each series wa s produced by an individual, in most cases by a mature male in a small grou p, and consisted of between 2 and 16 codas, emitted in one or more "bursts" of 1 to 13 codas spaced fairly regularly in time. The mean number of codas in a burst was 3,46, and the standard deviation was 2.65. The time interva l ratios within a coda are parameterized by the coda duration and by the fi rst two interclick intervals normalized by coda duration. These three param eters remained highly stable within each coda series, with coefficients of variation within the series averaging less than 5%, The interval ratios var ied somewhat across the data sets, but were highly stable over 8 of the 11 data sets, which span 11 years and widely dispersed geographic locations. S omewhat different interval ratios were observed in the other three data set s; in one of these data sets, the variant codas were produced by a young wh ale. Two sets of presumed sperm whale codas recorded in 1996 had 5- and 6-c lick patterns; the observation of these new patterns suggests that sperm wh ale codas in the Mediterranean may have more variations than previously bel ieved, (C) 2000 A coustical Society of America. [S0001-4966(00)02706-5].