The forests (and wooded suburbs) are home to a variety of invertebrate and vertebrate animal species. The state has an abundance of white-tailed deer, and there have been concerns about deer overpopulation because many of the deer's natural predators, such as wolves, have historically been hunted to extinction within Massachusetts. However, coyotes have been moving into Massachusetts to fill the ecological niche formerly occupied by wolves. Bears, wild turkey, and even moose have returned from northern refuges. In 1846 Thoreau traveled to Northern Maine to observe and write about moose, which he thought were well on the way to extinction. If he were alive today, he might find them almost within walking distance of Walden Pond.