Effects of Single- and Mixed-Species Group Composition on the Flight Initiation Distances of Plains and Grevy's Zebras

Zebras, as prey species, attend to the behavior of nearby conspecifics and heterospecifics when making decisions to flee from predators. Plains zebras (Equus quagga) and Grevy's zebras (E. grevyi) frequently form mixed-species groups in zones where their ranges overlap in Kenya. Although anecdotal observations suggest that Plains zebras are more flighty around humans than Grevy's zebras are, this has not been empirically confirmed, and relatively little is known about how they may influence each other's flight behavior. We addressed these questions by examining the flight initiation distances (FIDs) of Plains and Grevy's zebras in single-species and mixed-species groups from an approaching human. One target individual per group was approached steadily on foot, with start distance, alert distance, and FID recorded from this target. Using start distance and alert distance separately as covariates, 22 Plains zebras in single-species groups exhibited a significantly longer mean FID than 15 Grevy's zebras in single-species groups. The FIDs of 7 Plains zebras and 5 Grevy's zebras tested in mixed-species groups were virtually equivalent and intermediate to those of Plains and Grevy's zebras in single-species groups, suggesting a bidirectional moderating influence of heterospecifics on risk assessment. This effect was most pronounced for Plains zebras in mixed-species groups that exhibited an FID that was significantly shorter than that of Plains zebras in single-species groups. Our findings underscore the importance of recognizing that related equids may be differently impacted by anthropogenic stress