Zebra reduce predation risk in mixed-species herds by eavesdropping on cues from giraffe

Giraffes may be more useful lookouts to zebras than other zebras. In mixed herds, zebras looked towards giraffes and spent less time scanning for danger themselves. The giraffes made no audible alarm calls during the observations, suggesting that any information was available through their behaviour rather than a shouted warning.

Melissa Schmitt, Keenan Stears and Adrian Shrader watched adult zebras in South Africa's Hluhluwe-iMfolozi and Kruger parks. They compared 77 zebras in 18 giraffe–zebra herds with 169 in 51 zebra-only herds. During three-minute observations, they recorded time spent alert and the direction and intensity of scans. A subset of observations examined whether zebras looked towards herd members or the surrounding landscape.

Zebras with giraffes spent about ten seconds alert per observation, versus 27 seconds in zebra-only herds. They also shifted attention towards herd members, particularly giraffes, instead of mainly scanning their surroundings. This observational comparison measured vigilance, not successful escapes or survival, and did not test which giraffe postures conveyed information. Even so, the pattern supports a role for giraffes as sources of threat information. Their height may provide an advantage that neighbouring animals can use without the giraffe deliberately warning them.