Dietary overlap between the burrowing bettong (Bettongia lesueur) and the European rabbit (Oryctolagus cuniculus) in semi-arid coastal Western Australia

The diets of burrowing bettongs and European rabbits were studied on Heirisson Prong at Shark Bay, Western Australia, over two winters (1996 and 1997) and two summers (1996/97 and 1997/98). This was during a period when the rabbit population was increasing to high levels and projected foliage cover was decreasing, presenting environmental conditions likely to exacerbate competition. The diets of bettongs and rabbits were significantly different in both winter and summer. The mean overlap in diets shifted from 43% in winter to 56% in summer. Bettongs were able to vary their diet in response to environmental conditions while rabbits perished in large numbers during the second summer. The winter diet of bettongs included hypogeal fungi (19-23%), fruit and forbs; their summer diet included seed, stem, and the foliage of shrubs. Grasses dominated the winter diet of rabbits; forbs, 'other shrub species', and browse from shrubs were included also. In summer, rabbits ate mainly roots (30-35%), browse and stems from shrub species. Bettongs ate food items that rabbits did not, and were better able to use common resources. The lack of significant dietary overlap between rabbits and bettongs suggests minimal competition at times of potentially limited food resources. These results suggest that rabbits alone are unlikely to have brought about the mainland extinction of bettongs.