We have been isolated by the ocean since before mammals spread globally. We have two native species of bat, these are our only native mammals. There are also fur seals and see lions but people don't seem to count them. When the Maori arrived about 800 years ago they brought rats with them. When the Captain Cook arrived he released goats and pigs. Since then a few game animals were released in the early 1900s, red, whitetail, fallow, sika, and rusa deer, wapiti, chamois and tahr.