The Rothschild's giraffe as a potential biological controller of invasive native Acacia species in Lake Mburo National Park, Uganda

Abstract

Shrub and woody encroachment can have serious ecological impacts and is an increasingly common problem in many ecosystems, from the African savanna to the Arctic. Lake Mburo National Park in Uganda is experiencing severe woody encroachment of the native invasive Acacia species. In 2015, 15 Rothschild’s giraffes (Giraffa camelopardalis rothschildi) were translocated to Lake Mburo as both a conservation effort to expand the range of the endangered giraffe subspecies and as part of a long-term project to control the encroachment of Acacia in the park. I investigated if giraffes could potentially act as biological controllers of the invasive Acacia species in the park by studying diet preferences and spatial feeding area selection on three scales: landscape, patch, and fine scale. Over 80% of the giraffes total diet consisted of Acacia, implying that the small population of giraffes consume more than 200 kg of dry-weight Acacia biomass on a daily basis. Giraffes selected for Acacia on all scales. On the landscape scale, giraffes foraged in areas with high densities and abundances of Acacia. On the patch scale, giraffes fed in homogenous, open areas. On the fine scale, giraffes selected for Acacia, utilizing it three times more than its availability. The giraffes also preferred to feed on Acacia trees that were 4-5 m tall, selecting taller than average individuals to feed on. This foraging behavior implies the potential for giraffes to act as biological controllers of the native invading Acacia species in Lake Mburo.