Birdwatchers can find the greatest numbers and diversity of birds in sanctuaries where there are few or no pests. You need a Department of Conservation permit to visit closed sanctuaries such as Kāpiti Island, whereas open sanctuaries can be visited more freely. Fenced sanctuaries – Zealandia, Maungatautari and others – exclude mammalian predators from hundreds or thousands of hectares. The birds can breed safely, although they are still free to fly in and out. Mainland islands are large unfenced areas within National Parks or other reserves where pests are well controlled. Most fenced sanctuaries and mainland islands are open to the public, and there are many ways to become involved as a volunteer.