The hairy woodpecker (Leuconotopicus villosus) measures from 18–26 cm (7.1–10.2 in) in length, 33–43 cm (13–17 in) in wingspan and 40–95 g (1.4–3.4 oz) in weight. It is virtually identical in plumage to the smaller downy woodpecker. The downy has a shorter bill relative to the size of its head, which is, other than size and voice, the best way to distinguish them in the field. These two species are not closely related, however, and are likely to be separated in different genera. Another way to tell the two species apart is the lack of spots on its white tail feathers (present in the downy). Their outward similarity is a spectacular example of convergent evolution. As to the reason for this convergence, only tentative hypotheses have been advanced; in any case, because of the considerable size difference, ecological competition between the two species is slight.