Can long-finned pilot whale social structure be accessed by their calls?

Abstract

The pulsed calls of long-finned pilot whales, Globicephala melas, are still poorly studied acoustic signals, they have complex structures and functions not yet understood, and these signals seem to be associated with a group's own language which makes them even more instigating. In this study, we investigated and compared the parameters of two groups of long-finned pilot whales that were recorded on two occasions during cetacean surveys of the Federal University of Rio Grande in partnership with the Aqualie Institute, aboard the R / V Atlântico Sul on the coast of Brazil, from the region of Chuí to Cabo Frio. The first acoustic recording occurred in May 26th, 2013 at 33º18'S – 50º16'W, while the second acoustic recording occurred in May 12th, 2014 at 33º27'S – 50º35'W. The acoustic recording system was composed by a 250m long towed array with three omnidirectional elements (-40 dB, - 161 dB re: 1V / μPa, Auset®), distant five meters apart and arranged five meters from the end of the cable. The array was connected to a digital recording system composed by a Fostex® FR-2 LE digital recorder (with sampling frequency of 96 kHz/ 24 bits and 48 kHz/ 24 bits, respectively and configured with a high pass filter of 1952 Hz). Spectral parameters of the fundamental component of each call such as initial frequency, final frequency, total duration, maximum frequency, minimum frequency variation were extracted using Raven Pro software 1.5. In order to validate whether the calls belonged to different groups, we used a Vector Support Machine (SVM), implemented in the program R. The result of discriminant analysis (SVM) was positive, where we obtained the separation of the calls in two groups (clans) with an error rate of 18.81%. In order to investigate possible social units within each clan found, a k-means analysis was used, and the results of this analysis pointed out possible social units from calls subsets indicating for the first time a possible complex social structure of the species Globicephala melas for the Western South Atlantic Ocean.