Migratory herds of wildebeests and zebras indirectly affect calf survival of giraffes

Giraffe calves can benefit from a migration they do not make. When herds of wildebeest and zebra move through their landscape, lions gain many alternative animals to hunt. That could spare resident giraffe calves—or attract more predators and make life harder. The two possibilities make opposite predictions about calf survival.

Derek Lee, Bernard Kissui, Yustina Kiwango and Monica Bond compared five areas of Tanzania's Tarangire ecosystem across three years and three seasons per year. Photographs tracked 449 calves and 860 adult females. The team combined estimated calf survival and numbers of young calves per female with local lion densities and counts of migratory prey. The decisive comparison was lions relative to available prey, not either count alone.

Calf survival was lower where lions were more numerous relative to wildebeest and zebra. The pattern supported a short-term protective effect of migratory herds, consistent with lions switching prey or having ample food. Individual kills were not tracked, and survival immediately after birth was inferred from calf numbers rather than observed directly. Even with those limits, the study exposes a connection easily missed by studying giraffes alone: losing another species' migration could also make growing up harder for giraffes.