Vocalizations of feeding humpback whales from southeast Alaska were analyzed to characterize quantitatively the predominant vocalization associated with feeding and assess variation among vocalizations. Whales uttered series of cries similar in acoustic structure to those described previously as stereotyped, rhythmic 'feeding calls'. Individual cries ranged in duration from 0.4 to 8.2 sec. (median = 2.6 sec). Cries typically had a short, strongly frequency modulated (FM) introductory and ending component (labeled Section A and C, respectively). Cries had relatively little FM over the main body of the call (labeled Section B) which ranged in fundamental frequency from 360 to 988 Hz (median = 553 Hz) and sometimes exhibited a frequency oscillation over a bandwidth of approximately 16 to 65 Hz. Principle components analysis indicated that most variation in the data-set (over 35%) could be attributed to measures of absolute frequency, however a substantial amount of variation was also due to other acoustic parameters such as duration, frequency oscillation and average slope of cry sections A and C. Within series, cries were stereotyped and varied little, whereas there was statistically significant variation in cries between series. Furthermore, overlapping cries, which are considered to represent the vocalizations of different individuals, varied significantly. These results suggest that whales may produce individually specific cries, and we propose two alternative hypotheses to account for our observations: 1) cries may carry individual signature information, and 2) simultaneously vocalizing animals may actively mismatch cries to maximize a herding elect on prey.
humpback whale, foraging, feeding vocalization, individual variation, multivariate