the migratory herd exhibits a wavy front, and this suggests that some degree of local decision-making is taking place. Numerous documentaries feature wildebeest crossing rivers, with many being eaten by crocodiles or drowning in the attempt. While having the appearance of a frenzy, recent research has shown a herd of wildebeest possesses what is known as a "swarm intelligence", whereby the animals systematically explore and overcome the obstacle as one. Ecology Predators Major predators that feed on wildebeest include the lion, hyena, African wild dog, cheetah, leopard, and crocodile, which seem to favour the wildebeest over other prey. Wildebeest, however, are very strong, and can inflict considerable injury even to a lion. Wildebeest have a maximum running speed of around . The primary defensive tactic is herding, where the young animals are protected by the older, larger ones, while the herd runs as a group. Typically, the predators attempt to isolate a young or ill animal and attack without having to worry about the herd. Wildebeest have developed additional sophisticated cooperative behaviours, such as animals taking turns sleeping while others stand guard against a night attack by invading predators. Wildebeest migrations are closely followed by vultures, as wildebeest carcasses are an important source of food for these scavengers. The vultures consume about 70% of the wildebeest carcasses available. Decreases in the number of migrating wildebeest have also had a negative effect on the vultures. In the Serengeti ecosystem, Tanzania, wildebeest may help facilitate the migration of other, smaller-bodied grazers, such as Thomson's gazelles (Eudorcas thomsonii), which eat the new-growth grasses stimulated by wildebeest foraging. Interactions with nonpredators Zebras and wildebeest group together in open savannah environments with high chances of predation. This grouping strategy reduces predation risk because larger groups decrease each individual's chance of being hunted, and predators are more easily seen in open areas. The seasonal presence of thousands of migratory wildebeests reduces local lion predation on giraffe calves, resulting in greater survival of giraffes. Wildebeest can also listen in on the alarm calls of other species, and by doing so, can reduce their risk of predation. One study showed, along with other ungulates, wildebeests responded more strongly to the baboon alarm calls compared to the baboon contest calls, though both types of calls had similar patterns, amplitudes, and durations. The alarm calls were a response of the baboons to lions, and the contest calls were recorded when