Interspecific and seasonal dietary differences of Himalayan thar, chamois and brushtail possums in the central Southern Alps, New Zealand

Himalayan thar or tahr (Hemitragus jemlahicus), Alpine chamois (Rupicapra rupicapra) and brushtail possums (Trichosurus vulpecula) are native to the Himalaya, Europe and Australia, respectively, but are now sympatric in parts of the central Southern Alps, New Zealand. All three species are managed as pests by the Department of Conservation. We analysed the diets of 246 thar, 78 chamois and 113 possums collected in the central Southern Alps during 1988–1996. The diets of thar and chamois strongly overlapped, but thar ate more grasses and less herbs and woody plants than chamois. The diet of possums differed from the diets of thar and chamois, containing a different suite of herbs and almost no grasses. The diets of thar, chamois and possums varied seasonally. Contrary to expectation, the diets of adult male and female thar were similar during the period when they are spatially segregated (October–May). Chamois sampled outside the thar range ate more species than those sampled inside the thar range, suggesting that the presence of thar modifies the diet of chamois. If managers wish to protect the dominant Chionochloa snow tussocks then thar should be controlled; chamois should be controlled to protect herbs such as Ranunculus spp.; and possums should be controlled if Podocarpus nivalis or Muehlenbeckia axillaris need to be protected. However, managers need to be aware of the potential for chamois to increase in abundance, at least in some sites, if thar are controlled to low abundance, and that this could lead to different impacts on plant populations.