Superbly adapted to the alpine environment of their original home in Nepal, thar have caused extensive damage to native alpine vegetation in the Southern Alps. Snow tussocks and other mountain grasses are particularly affected by thar browsing. Thar also graze on woody plants, including native broom, and mountain herbs such as the Mt Cook buttercup – one of the most renowned and most beautiful of New Zealand’s alpine plants.

Since their introduction, thar have colonised alpine areas in most of Canterbury and the West Coast, and a small part of Otago. Their range includes three national parks and other conservation lands that fall within the Te Wahipounamu World Heritage Area.

Today, under the National Himalayan Thar Control Plan (1993), thar are kept to low numbers through a combination of recreational and commercial hunting. The thar population is now around 7000–8000 animals. Left uncontrolled the population would rise to over 50,000 animals. Official culling operations may be carried out by the Department of Conservation when thar numbers rise above ‘intervention’ densities.

New Zealand Biodiversity Strategy (NZBS) funding has ensured that the thar plan is meeting its objectives of controlling thar numbers, preventing southward spread, and, monitoring the impacts of thar.

An important focus of the NZBS-funded thar control programme is to prevent the southward spread of thar, which currently range as far as Lake Hawea. A ‘Southern Exclusion Zone’ was established by the national plan, and thar control efforts are aimed at ensuring removal of all thar that enter the zone, which lies largely within Mount Aspiring National Park south of the Haast River, and west of the Makarora River and Lake Wanaka.

To keep thar from the zone, culling efforts are being concentrated over a 176,000-hectare area, which encompasses the Landsborough, Hunter and Dingle Burn valleys. Since 1994, the Otago conservancy has successfully used the so-called ‘Judas’ technique for locating thar herds by tracking individual thar fitted with radio-collars.

The Judas technique has been both successful and cost-effective in areas where thar numbers are very low. Over 70 per cent of thar seen with judas animals have been shot, and a recent review* showed that using the technique can halve control costs when compared with the traditional method of searching for the animals from the air.

In 2002/03, NZBS funded thar control will occur in Canterbury, Otago and the West Coast, and will include a programme to eradicate thar from Otago’s Thompson Mountains.

*Department of Conservation (2001). Use of Judas Thar in Otago – The First Five Years (1994–1999). Department of Conservation, Wellington.