Tammar wallabies became extinct on mainland South Australia in the 1930's. Extinction has been caused by habitat destruction, hunting, and foxes. In 1998 a small population of South Australian wallabies was found living on Kawau Island near Auckland, in New Zealand. This group had been established by former South Australian governor, Sir George Grey in 1862 as part of his own private zoo. In New Zealand these wallabies were seen as a pest, and scientists have been studying ways to get rid of them. 85 wallabies were taken back to South Australia. After extensive fox controls at Innes National Park, 10 wallabies were released in November 2004. Another 36 were released in June 2005. These first releases were tracked with radio collars. Another group has been put into a captive breeding program at Monarto Zoo.