The family Picidae consists of over 200 species that are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar, and the polar regions. Since they have over two hundred species in the family–they make up about half the total number of species in the order Piciformes.
The Picidae family consists of woodpeckers, flickers, sapsuckers, wrynecks, and piculets.
The wyrnecks are found in Eurasia and Africa, the piculets are found in Asia, Central & South America in addition to Hispaniola. The woodpeckers, flickers, and sapsuckers have a more widespread distribution.
Each species has their own individual range, and some species ranges overlap, while others are restricted.
In terms of their habitat, for the most part they are found in forests (including tropical rain forests), but also woodlands, savannas, scrub-lands, deserts, city parks, plantations, and basically any place where there are trees and/or cacti.
While they mostly eat insects and other invertebrates (such as spiders), they will also eat nuts, fruits, sap (main food source for the sapsuckers), and insects on the ground as well (such as the wyrnecks). The diet varies depending on the species, location, and individual preference of the bird.
Since the woodpeckers go after insects and grubs on the trees by pecking holes into the bark, their beak consists of three layers: an outer sheath comprised of kertain proteisn (alled the rhamphotheca), an inner layer which has both a large cavity and mineralized collagen fibers, and a middle layer of porous bone that connects the inner and outer layers.
The main thing that makes woodpeckers unique is that their tongue-bone actually winds around the skull and cushions the brain against the constant vibration of them pecking at the bark. This allows for the beak to absorb the mechanical stress of pecking holes into the bark.
So within the United States, Canada, and Mexico the following species are the ones that you are most likely to see:
Some interesting little tidbits about woodpeckers found in the US, Canada & Mexico:
The ivory-billed woodpecker was once thought to be extinct, but is now listed as critically endangered after being spotted in 2004 & 2005 in a small area in Arkansas.
The Gila woodpecker actually makes use of cacti instead of trees for nesting sites, as they are found in the deserts of the southwest US and northwest Mexico.
Lewis’s woodpecker actually goes after flying insects (such as flies and nosquitoes) instead of hunting for insects on trees.
In terms of being in danger of extinction–there are three species (worldwide) that are listed as critically endangered: the ivory-billed, imperial, and Okinawa woodpeckers a a result of the loss of old growth forests. Four other woodpeckers (again worldwide) are listed as vulnerable: the red-cockaded, Arabian, helmeted, and Sulu woodpeckers again due to habitat loss. There are also numerous wyrneck and picoulet species that are also listed as vulnerable or low risk–again due to habitat loss.
The constant expansion of cities and towns into wooded areas is the one main driving force against these birds. Unlike other birds that eat seed (yes, woodpeckers do visit suet and seed feeders)–these birds need old trees for both foraging and nesting. Protection of forests is needed to keep these birds from sliding into extinction.
References: https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/woodpeckers-wrynecks-and-piculets-picidae & https://en.wikipedia.org/wiki/woodpecker