Influence of variation in nutritional content and distribution of wild and crop species on crop raiding by Mountain Gorillas in Bwindi Impenetrable National Park, Uganda

Abstract

Crop raiding by wild animals is a concern for protected area managers and neighbouring communities. Mountain gorillas normally prioritise energy and sodium in their diet; a mineral that is deficient in their natural diet, leading to crop raiding. The study examined the influence of nutritional differences of wild and crop plant species on crop raiding by Mountain Gorillas in Bwindi Impenetrable National Park, Uganda. The study aimed at contributing to a better understanding of the nutritional motivation for Mountain Gorillas exiting the National Park and raiding crops. Data was collected for period of six months from August 2012 to January 2013. Focal follows on one habituated gorilla group were used to collect data on the wild plant species eaten by Mountain gorillas. Plant samples were further collected and analysed for nutritional composition using Near Infra-red Spectroscopy while distribution of food plant species was determined along established transects using Principal component Analysis. Twenty-five wild plant species which the gorillas fed on were recorded inside the park. Nineteen species were recorded outside the park while fourteen wild plant species were recorded both inside the park and on community land. Leaves were the major plant part of wild foods eaten by gorillas. Only Eucalyptus grandis and Musa spp were observed to have been raided. There were no significant differences in the proportions of Total Non-structural Carbohydrates (TNC), proteins, fat and Neutral Detergent Fibre (NDF) between the crops which were raided and those which were not raided. There was no significant difference in the proportion of NDF and protein between crops and forest foods eaten by gorillas, while crops which were raided had more sugar than forest foods. There was no significant difference in the composition of mineral elements between the eaten crops and those which were not eaten. However, E. grandis had the highest concentration of sodium while Musa spp pith had a higher concentration of potassium. The palatable food plant species were distributed far from the park boundary ( ≥ 500 metres) while non-palatable crop foods species were found close (< 500 metres) to the park. The presence of preferred wild and crop foods rich in sugar may possibly explain the main reason for gorillas venturing outside the park. Therefore, growth of unpalatable crops such as Coffea robusta, Camellia sinensis and Cymbopogon spp should be promoted in areas near the park while crops palatable to gorillas should be grown far (≥ 500 metres) from the park boundary.