Threats and degradationĪcorn woodpeckers, like many other species, are threatened by habitat loss and degradation. Once all the females start to lay, they stop removing eggs. A female usually destroys any eggs in the nest before she starts to lay. In groups with more than one breeding female, the females put their eggs into a single nest cavity. Inbreeding is rare, however, meaning that co-breeders of the opposite sex are almost never related. The males are often brothers, and the females are usually sisters. Interestingly, these breeding coalitions are typically closely related. Nesting groups can also contain up to ten offspring helpers. It is generally believed that limited territories drive cooperative breeding behavior in birds, and in the case of the acorn woodpecker, this limited territory is the acorn storage granary.Īs mentioned, adult acorn woodpeckers live together in "coalitions", which consist of up to seven co-breeding males and up to three joint-nesting females however, most nests are made up of only three males and two females. Additionally, adult offspring often stay in their parents' nest and help raise the next generation of woodpeckers. Coalitions of adult acorn woodpeckers nest together, localizing to storage granaries. With the acorn woodpecker, cooperative breeding occurs in two ways: coalitions and family groups. Cooperative breeding is defined as more than two birds taking care of nestlings in the nest. Breeding behaviorĪcorn woodpeckers practice cooperative breeding, which is a relatively rare evolutionary trait that is thought to occur in only nine percent of bird species. If the stores are eaten, the woodpecker will move to another area, even going from Arizona to Mexico to spend the winter. In parts of its range the acorn woodpecker does not construct a "granary tree", but instead stores acorns in natural holes and cracks in bark. Woodpeckers put 220 kg (490 lb) of acorns into a wooden water tank in Arizona. Occasionally the woodpecker will put acorns into places where it cannot get them out. The acorn woodpecker will use any human-made structures to store acorns, drilling holes into fence posts, utility poles, buildings, and even automobile radiators. Acorn woodpeckers can also be seen sallying from tree limbs to catch insects, eating fruit and seeds, and drilling holes to drink sap. Acorns are such an important resource to the California populations that acorn woodpeckers may nest in the fall to take advantage of the fall acorn crop, a rare behavior in birds. The acorns are visible, and the group defends the tree against potential cache robbers like Steller's jays and western scrub jays. They also feed on insects, sap, and fruit. As acorns dry out, they are moved to smaller holes and granary maintenance requires a significant amount of the bird's time. The woodpeckers then collect acorns and find a hole that is just the right size for the acorn. In some parts of their range (e.g., California), the woodpeckers create granaries or "acorn trees" by drilling holes in dead trees, dead branches, telephone poles, and wooden buildings. Food and homesĪcorn woodpeckers, as their name implies, depend heavily on acorns for food. Young from a single brood have been found with multiple paternity.
#Acorn woodpecker cornell plus#
A group of adults may participate in nesting activities: field studies have shown that breeding groups range from monogamous pairs to breeding collectives of seven males and three females, plus up to 10 nonbreeding helpers. The breeding pair excavate a nest in a large cavity in a dead tree or a dead part of a tree. 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. The breeding habitat is forested areas with oaks in the hills of coastal areas and foothills of California and the southwestern United States south to Colombia. Acorn woodpeckers have a call that is almost like they are laughing. White circles on their wings are visible when in flight. When flying, they take a few flaps of their wings and drop a foot or so. The white neck, throat, and forehead patches are distinctive identifiers. The adult male has a red cap starting at the forehead, whereas females have a black area between the forehead and the cap. There is a small part on the small of their backs where there are some green feathers. The adult acorn woodpecker has a brownish-black head, back, wings and tail, white forehead, throat, belly and rump.
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