The woodpeckers have a mostly cosmopolitan distribution, although they are absent from Australasia, Madagascar and Antarctica. They are also absent from the world's oceanic islands, although many insular species are found on continental islands. The true woodpeckers, subfamily Picinae, are distributed across the entire range of the woodpeckers. The Picumninae piculets have a pantropical distribution, with species in Southeast Asia, Africa and the Neotropics, with South America holding the majority of piculet species. The second piculet subfamily, Nesoctitinae, has a single species, the Antillean Piculet, which is restricted to the Caribbean island of Hispaniola. The wrynecks (Jynginae) have an exclusively Old World distribution, with the two species occurring in Europe, Asia and Africa.
Overall the woodpeckers are arboreal birds of wooded habitats. They reach their greatest diversity in tropical rainforests, but occur in almost all suitable habitats including woodlands, savannahs, scrublands, bamboo forests. Even grasslands and deserts have been colonised by various species. These habitats are more easily occupied where a small number of trees exist, or, in the case of desert species like the Gila Woodpecker, tall cacti are available for nesting in. A number of species are adapted to spending a portion of their time feeding on the ground, and a very small minority of species have abandoned trees entirely and nest in holes in the ground. The Ground Woodpecker is one such species, inhabiting the rocky and grassy hills of South Africa.
Picidae species can either be sedentary or migratory. Many species are known to stay in the same area year-round while others travel great distances from their breeding grounds to their wintering grounds. For example, the Eurasian Wryneck breeds in Europe and west Asia and migrates to the Sahel in Africa in the winter.
The woodpeckers range from highly antisocial solitary species which are aggressive to other members of their species to group living species. Group living species tend to be communal group breeders. In addition to these species a number of species may join mixed-species feeding flocks with other insectivorous birds, although they tend to stay at the edges of these groups. Joining these flocks allows woodpeckers to decrease anti-predator vigilance and increase their feeding rate. Woodpeckers are diurnal, roosting at night inside holes. In most species the roost will become the nest during the breeding season.
Diet and feeding
The diet of woodpeckers consists mainly of insects and their grubs, and other arthropods, along with fruit, nuts and sap. The family is noted for its ability to acquire wood-boring grubs using their bills for hammering, but overall the family is characterised by its dietary flexibility, with many species being both highly omnivorous and opportunistic. The insect prey most commonly taken are insects found inside rotten wood and in crevices in bark on trees. These include beetles and their grubs, ants, termites, spiders,and caterpillars. These may be obtained either by gleaning or more famously by excavating wood. Having hammered a hole into the wood the prey is excavated by a long barbed tongue. The ability to excavate allows woodpeckers to obtain tree sap, an important source of food for some species. Most famously the sapsuckers, (genus Sphyrapicus ) feed in this fashion, but the technique is not restricted to these and others such as the Acorn Woodpecker also feed in this way. It was once thought that the technique was restricted to the New World, but Old World species such as the Arabian Woodpecker and Great Spotted Woodpecker also feed in this way.
All members of the family Picidae nest in cavities. Almost every species nests in tree cavities, although in deserts some species nest inside holes in cactus and a few species nest in holes dug into the earth. Woodpeckers and piculets will excavate their own nests, but wrynecks will not. The excavated nest is usually only lined from the wood chips produced as the hole was made. Many species of woodpeckers excavate one hole per breeding season, sometimes after multiple attempts. It takes around a month to finish the job. Abandoned holes are used by many other birds and mammals which are secondary cavity nesters.
Members of Picidae are typically monogamous, with a few species breeding cooperatively and some polygamy reported in a few species. Polyandry, where a female raises two broods with two separate males, has also been reported in the West Indian Woodpecker. A pair will work together to help build the nest, incubate the eggs and raise their altricial young. However, in most species the male does most of the nest excavation and takes the night shift while incubating the eggs. A nest will usually consist of 2-5 round white eggs. Since these birds are cavity nesters, their eggs do not need to be camouflaged and the white color helps the parents to see them in dim light. The eggs are incubated for about 11–14 days before the chicks are born. It takes about 18–30 days before the young are ready to leave the nest.
The phylogeny has been updated according to new knowledge about convergence patterns and evolutionary history. Most notably, the relationship of the picine genera has been largely clarified, and it was determined that the Antillean Piculet is a surviving offshoot of proto-woodpeckers.
The evolutionary history of this group is not well documented, but the known fossils allow some preliminary conclusions: the earliest known modern picids were piculet-like forms of the Late Oligocene, about 25 million years ago (mya). By that time, however, the group was already present in the Americas and Europe, and it is hypothesized that they actually evolved much earlier, maybe as early as the Early Eocene (50 mya). The modern subfamilies appear to be rather young by comparison; until the mid-Miocene (10-15 mya), all picids seem to have been small or mid-sized birds similar to a mixture between a piculet and a wryneck. On the other hand, there exists a feather enclosed in fossil amber from the Dominican Republic, dated to about 25 mya, which seems to indicate that the Nesoctitinae were already a distinct lineage by then.
Prehistoric representatives of the extant Picidae genera are treated in the genus articles. An enigmatic form based on a coracoid found in Pliocene deposits of New Providence, Bahamas, has been described as Bathoceleus hyphalus and probably also is a woodpecker.