Impacts of large mammals on bird diversity and abundance in an African savanna

Large native mammals are declining dramatically in abundance across Africa, with strong impacts on both plant and animal community dynamics.  For example, the biomasses of herbivorous small mammals, insects, carnivorous snakes, lizards, and grasses increase where native large mammals are excluded.  Yet the net effects of this large-scale loss in megafaunal diversity are poorly understood because responses by several ecologically important groups have not been assessed.  We used a large-scale, replicated exclusion experiment in Kenya to investigate the impacts of different guilds of native and domestic large mammalian herbivores on diversity and abundance of birds over a two-year period. The exclusion of large herbivorous wild mammals, including zebras (Equus burchelli), giraffes (Giraffa camelopardalis), elephants (Loxodonta africana), and buffalos (Syncerus caffer), increased the diversity of birds by 30%. Most of this effect was attributable to the absence of elephants and giraffes; these megaherbivores reduced both the canopy area of woody vegetation and the biomass of ground-dwelling arthropods and both of these factors were good predictors of the diversity of birds. The canopy area of trees was positively correlated with the abundance and diversity of birds regardless of whether they were foliage gleaners, bark gleaners, or ground foragers. The biomass of ground-dwelling arthropods was positively correlated with the abundance and diversity of insectivorous birds.  Our results suggest that most native large herbivores are compatible with an abundant and diverse bird fauna, as are cattle if they are at a relatively low stocking rate. Although megaherbivores reduced local bird diversity, our results suggest that landscapes composed of areas with a range of elephant densities would support higher regional bird diversity than would landscapes devoid of elephants.