Vigilance behavior in plains zebra (Equus burchelli): An analysis of group size, synchrony and the implications of tourism

Abstract

The advantages of group living in ungulates are well studied. One such advantage is that as group size increases, vigilance levels decrease; therefore, animals are able to spend more time grazing while maintaining a low predation risk. The purpose of this paper is to determine the relationship between group size and vigilance behavior in plains zebra (Equus burchelli). We also investigate if and how the zebra synchronize their vigilance behavior. Using a remote control simulated predator, we tested zebras’ response to a simulated predator and non-predator. We found that individual vigilance levels decreased as a function of group size, resulting in an increase in the proportion of time zebra spent grazing, thereby supporting previous research on ungulates. In addition, protection from predation increased with group size. We also found that redundancy did not increase with group size suggesting that the zebra are not behaving independently of each other; yet, they are also not behaving antiphonally, which is the optimal form of synchronization. In conjunction with our findings that the average distance between two alert individuals increased with group size as well as the likelihood that two alert individuals were adjacent to each other was higher than expected, we suggest that the zebra attend and respond to the actions of their nearest neighbors. Furthermore, we propose a hypothesis that individuals may not always trust the vigilance of others, double-checking on what their neighbor responds to in order to confirm there is no threat. The zebra distinguished between a potential predation attack, a simulated lion, and a nonthreatening disturbance, a simulated zorilla and monkey. The zebra detected the lion earlier than both the zorilla and monkey and also ran earlier and further from the lion as compared to the zorilla and monkey. We found no difference in vigilance behavior between the east side of the conservancy, which is frequented by tourists, and the west side of the conservancy, where tourists rarely go. We propose that tourism does not have a negative impact on the animals, but future research on the impact of tourism should be done on a finer scale than ours.