In New Zealand the first invasive species were the dogs and rats brought by Polynesian settlers around 1300. Cats, brought later by Europeans, have had a devastating effect upon the native birdlife, particularly as many New Zealand birds are flightless. Rabbits, introduced as a food source by sailors in the 1800s, have become a severe nuisance to farmers, notably in the South Island. Common gorse, originally a hedge plant native to Western Europe, was introduced to New Zealand for the same purpose but grows aggressively and threatens to obliterate native plants in much of the country and is hence routinely eradicated. The native forests are heavily impacted by several species of deer from North America and Europe and by the Australian brushtail possum. These exotic species have all thrived in the New Zealand environment.