The nuthatches are a small family of birds, which share a distinctive mode of movement, running down trees or rock faces - headfirst; they rarely run back up though. Small dumpy birds they share a longish bill, strong legs and feet and a short tail (which isn't used for support) and most are similarly coloured with slate blue backs and pale underparts. They feed mostly on insects gleaned from crevices in the bark or the rocks. They are distributed throughout the northerm hemisphere and most are very sedentary, only moving a few kilometres in their lifetime. Most species are monogamous and territorial, but they will join mixed species flocks, particularly with tits during the non-breeding season.