Classifying humpback whale individuals from their nocturnal feeding-related calls

Abstract

A large number of humpback whale vocalizations, comprising of both songs and non-song calls, were passively recorded on a high-resolution towed horizontal receiver array during a field experiment in the Gulf of Maine near Georges Bank in the immediate vicinity of the Atlantic herring spawning ground from September to October 2006. The non-song calls were highly nocturnal and dominated by trains of “meows,” which are downsweep chirps lasting roughly 1.4 s in the 300 to 600 Hz frequency range, related to night-time foraging activity. Statistical temporal-spectral analysis of the downsweep chirps from a localized whale group indicate that these “meows”can be classified into six or seven distinct types that occur repeatedly over the nighttime observation interval. These meows may be characteristic of different humpback individuals, similar to human vocalizations. Since the “meows” are feeding-related calls for night-time communication or prey echolocation, they may originate from both adults and juveniles of any gender; whereas songs are uttered primarily by adult males. The meows may then provide an approach for passive detection, localization and classification of humpback whale individuals regardless of sex and maturity, and be especially useful for night-time and/or long range monitoring and enumeration of this species.