A large variety of bird species can be found on Dartmoor including ones that have declined elsewhere in the UK, such as skylark and snipe, or are even rare nationally, such as the ring ouzel and the cuckoo. There are internationally important populations of meadow pipit and stonechat. Woodland birds include a number of migrant species, like the pied flycatcher, the wood warbler or the common redstart. Mammals found here include otters, hazel dormice and nearly all of the UK's 16 bat species. Three rare species, the barbastelle, and the greater and lesser horseshoe bats are of particular importance. The upper reaches of the rivers, are spawning grounds for Salmon and trout and Palmate newts, frogs and toads breed in the numerous small pools. Two shrimp species can be found on Dartmoor: fairy shrimp that can be found in temporary pools and in underground streams very rare cave shrimp. The world's largest land slug, the Ash black, is also found. Reptiles include common lizards and adders. The farmland in the wet valleys around the edge of the moors is the most important habitat for insects