Nonlinear phenomena in pinnipeds: a preliminary investigation in the contact calls of northern elephant seal pups.

As acoustic markers of emotional state, nonlinear phenomena (NLP) are commonly found in the calls that young mammals produce to solicit attention from their parents. However, data are lacking to assess the ontogeny of these NLP during early development, including the extent to which these acoustic cues vary with the age and sex of the emitter. In the present study, we evaluated the occurrence of NLP in the contact calls that northern elephant seal (Mirounga angustirostris) pups emit to solicit maternal care during the three-week period of maternal dependence. We found that five types of NLP are present at an early age. The relative occurrence of these NLP types varies with pup age, with more biphonation, chaos and subharmonics as pups get older, and fewer vibrato-like frequency-modulated components varying with both age and sex. Our results suggest that developmental changes-including body growth-facilitate increased flexibility in the vocal apparatus, which subsequently impacts the production of certain types of NLP. The production of nonlinear components within the calls of rapidly growing elephant seal pups is likely linked to their arousal state, which in turn is related to their high demand for maternal care. This can fluctuate throughout the lactation period and vary between male and female pups.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.