Serengeti birds maintain forests by inhibiting seed predators.

Of fundamental interest in conservation ecology are the regulatory mechanisms that maintain communities. We document a mechanism that maintains forests in the Serengeti ecosystem, Tanzania, and the destabilization when disturbance opens forest canopy. Forest birds, by consuming seeds, protected them from beetle attack. Consumption increased the germination rate and the density of seedlings and recruits, which was sufficient to maintain the forest. Opening of the canopy resulted in loss of birds, increased beetle attack, and loss of germination. Thus, frugivorous birds are necessary for the maintenance of forests. Their absence could have resulted in the observed forest decline since 1966.