Though it is primarily a full-time resident of northern and subalpine conifer forests, the red-breasted nuthatch regularly migrates irruptive, with both the number migrating and the wintering locations varying from year to year. They sometimes reach northern Mexico, where they are rare winter visitors to Nuevo León, Baja California Norte and south along the Pacific slope as far as Sinaloa. In the eastern United States, its range is expanding southwards.
Despite the other species’ common name, the brown-headed nuthatch is about the same size as the pygmy nuthatch and the two species are the world’s smallest nuthatches. In the brown-headed nuthatch, the total length is 9–11 cm (3.5–4.3 in), wingspan is 16–18 cm (6.3–7.1 in) and body mass is 10–12 g (0.35–0.42 oz)