[citation needed] It is found across Central America, as well as North into the western United States and South into parts of Colombia.

[1] The acorn woodpecker was formally described in 1827 by the English naturalist William Swainson under the binomial name Picus formicivorus from a specimen collected in Mexico.

[8] Seven subspecies are recognised:[7] The adult acorn woodpecker has a brownish-black head, back, wings and tail, white forehead, throat, belly and rump.

[10] This species may occur at low elevations in the north of its range, but rarely below 1,000 m (3,300 ft) in Central America, and it breeds up to the timberline.

However, reproductive vacancies—formed when all the breeders of one sex die—are filled by unrelated birds from elsewhere, so inbreeding is rare, despite the high degree of relatedness among most group members.

[19] Acorns are stored in small holes drilled especially for this purpose in "granaries" or "storage trees"—usually snags, dead branches, utility poles, or wooden buildings.

The following year, 1977, there was a significant increase in acorn production and a correlating decrease in non-breeding adults per unit.

They can be seen sallying from tree limbs to catch insects, eating fruit and seeds, and drilling holes to drink sap.

As acorns dry out, they are moved to smaller holes and granary maintenance requires a significant amount of the bird's time.

The acorns are visible, and a group defends its granary against potential cache robbers like Steller's jays and western scrub-jays.

If the acorn crop is poor and birds cannot find enough to store, the woodpeckers will move to other areas over the winter.