Contact Calls Facilitate Group Contraction in Free-Ranging Goats (Capra aegagrus hircus)

Lisa R O'Bryan,Simon Garnier,Guy Cowlishaw,Shinnosuke Nakayama,Nicole Abaid,Daniel I Rubenstein,Andrew J King,Tanujit Dey

doi:10.3389/fevo.2019.00073

Abstract

Many social animal species produce vocalizations believed to facilitate group contraction when one or more group members have become distant. However, the mechanisms underlying this function remain unclear for many species. We examined this question with data on a semi-free ranging group of 16 adult domesticated goats (Capra aegagrus hircus) inhabiting Tsaobis Nature Park, Namibia. All goats wore dataloggers consisting of a GPS and audio recorder for 5-6 hours per day for 10 days, providing continuous data on their geolocations and vocal communication. We found that callers were farther from the group centroid than expected by chance and that call production was associated with the cessation of group expansion and subsequent group contraction. We did not find strong evidence for antiphonal call exchange between distant and core group members. Rather, we found that (i) call production by distant group members is associated with a significant reduction of group movement away from the caller, and (ii) call production by core group members is associated with greater, though not significantly greater, group movement towards the caller. These findings suggest that calls may be used by distant, and potentially core, group members to facilitate the contraction of group spread. Results from our study clarify the mechanisms through which social animals can regulate collective movement behavior and the specific role that vocalizations play in this process.

Highlights

Animals can gain many benefits from remaining cohesive with others, such as greater protection from predators, more opportunities for mating and access to social information on the locations of resources (van Schaik, 1983; Dehn, 1990)
We first tested whether these calls were associated with periods of wide group spread while gaining insight into the positions of group members producing these calls
We found evidence that these vocalizations were associated with contexts in which group spread was especially wide, with group members that were further from the centroid being more likely to produce the calls

Summary

Introduction

Animals can gain many benefits from remaining cohesive with others, such as greater protection from predators, more opportunities for mating and access to social information on the locations of resources (van Schaik, 1983; Dehn, 1990). One category of contact call includes loud calls which individuals produce primarily when they have become distant from some or all group members (Rendall et al, 2000; GrosLouis et al, 2008). This type of contact call is often termed a “lost call” and is believed to play a role in helping the caller(s) to regain contact with group members (Cheney et al, 1996; Fischer et al, 2001; Digweed et al, 2007). Despite numerous studies of loud contact calling behavior in a variety of species, how these calls facilitate the contraction of group spread (hereafter “group contraction”) remains poorly understood, largely due to the difficulty of monitoring the vocal and movement behaviors of multiple group members simultaneously and due to the typical subtlety of any behavioral changes (Cheney et al, 1996)

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