Female harbor seal (Phoca vitulina) behavioral response to playbacks of underwater male acoustic advertisement displays.

Leanna P Matthews,Susan E Parks,Brittany Blades

doi:10.7717/peerj.4547

Abstract

During the breeding season, male harbor seals (Phoca vitulina) make underwater acoustic displays using vocalizations known as roars. These roars have been shown to function in territory establishment in some breeding areas and have been hypothesized to be important for female choice, but the function of these sounds remains unresolved. This study consisted of a series of playback experiments in which captive female harbor seals were exposed to recordings of male roars to determine if females respond to recordings of male vocalizations and whether or not they respond differently to roars from categories with different acoustic characteristics. The categories included roars with characteristics of dominant males (longest duration, lowest frequency), subordinate males (shortest duration, highest frequency), combinations of call parameters from dominant and subordinate males (long duration, high frequency and short duration, low frequency), and control playbacks of water noise and water noise with tonal signals in the same frequency range as male signals. Results indicate that overall females have a significantly higher level of response to playbacks that imitate male vocalizations when compared to control playbacks of water noise. Specifically, there was a higher level of response to playbacks representing dominant male vocalization when compared to the control playbacks. For most individuals, there was a greater response to playbacks representing dominant male vocalizations compared to playbacks representing subordinate male vocalizations; however, there was no statistical difference between those two playback types. Additionally, there was no difference between the playbacks of call parameter combinations and the controls. Investigating female preference for male harbor seal vocalizations is a critical step in understanding the harbor seal mating system and further studies expanding on this captive study will help shed light on this important issue.

Highlights

Acoustic communication is a critical component for reproductive success in a wide range of species: males can use reproductive signals to attract females or defend territories against other males
Female harbor seals approached the playback speaker significantly more during the LL playback when compared to the control (W) (p = 0.021)
For the second year of playbacks, there was no difference in the number of approaches to the speaker for any of the stimuli (SL, LH, W, and with the tonal signals (WT)), with overall low numbers of approaches to all stimuli, including controls

Summary

Introduction

Acoustic communication is a critical component for reproductive success in a wide range of species: males can use reproductive signals to attract females or defend territories against other males (for reviews, see Searcy & Andersson, 1986; Andersson, 1994). Females of some species have been shown to prefer signal traits that reflect honest indicators of male size, dominance status, or energetic reserves. Female red deer (Cervus elaphus) prefer calls with a lower frequency, which correspond to males of larger size (Charlton, Reby & McComb, 2007). Female tungara frogs (Physalaemus pustulosus) prefer calls with a lower frequency, indicating a preference for larger males (Ryan, 1980). Female Hermann’s tortoises (Testudo hermanni) prefer fast-rate acoustic displays, which are related to hematocrit levels in males and represent high quality mates (Galeotti et al, 2005)

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Conclusion