| Acorn Woodpecker | |
|---|---|
 | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Piciformes |
| Family: | Picidae |
| Genus: | Melanerpes |
| Species: | Melanerpes formicivorous |
The Acorn Woodpecker (Melanerpes formicivorous) is a bark-foraging bird in the family Picidae.
Description[]
Acorn Woodpeckers are mostly black above with a red cap. Medium-sized with straight bills like a spike are just these woodpeckers. Those stiff tails are what they use for clinging to tree trunks.
Behavior[]
Acorn Woodpeckers are very unusual woodpeckers that live in large groups, hoard acorns, and breed cooperatively. They have such complicated social behavior that they have given rise to one of the longest-running behavioral studies of birds. Group members gather acorns by the hundreds and wedge them into holes they’ve made in a tree trunk or telephone pole. Throughout the year, Acorn Woodpeckers collect acorns and wedge them tightly into holes they’ve made in tree bark. Acorn Woodpeckers fiercely defend these acorn granaries against other groups and any other species that might rob the stores. They also defend 15-acre territories around the granary. They occasionally wander outside the territory in pursuit of acorns and water.
Feeding[]
Acorn Woodpeckers eat acorns and insects (and other arthropods). They harvest acorns directly from oak trees and are famous for their habit of storing nuts—primarily acorns, but also almonds, walnuts, hazelnuts, pecans, and pinyon pine nuts—in individually drilled holes in one or more storage trees. These are known as granaries and can have upwards of 50,000 nuts stored in them. The birds drill the holes primarily in the winter, in the thick bark of dead limbs where the drilling does no harm to a living tree. Each year they reuse old holes and add some new ones. The acorns are wedged so tightly in their holes that they’re very difficult for other animals to remove. After they’ve been stored for a while, the fit becomes looser as the acorn dries out—group members periodically check their stored acorns and move the loose ones to smaller holes. Besides converting many kinds of live and dead trees into granaries, Acorn Woodpeckers often store acorns in structures like utility poles, fenceposts, and wood-sided buildings—a practice that has brought them into conflict with more than a few protective homeowners. Despite their association with acorns, Acorn Woodpeckers prefer to catch flying insects when those are available. They hunt for ants, beetles, and other insects by flying out from high perches. They may hunt insects at any time of year, often storing them in cracks or crevices. Besides nuts and insects, Acorn Woodpeckers also eat fruit, sap, oak catkins, and flower nectar, along with occasional grass seeds, lizards, and even eggs of their own species. In the spring they gather in groups to suck sap from small, shallow holes in tree bark, often using the same sets of sap holes for several years.
Breeding and Nesting[]
They live in family groups of up to a dozen or more individuals, and they cooperate in raising young and in gathering, storing, and guarding food. Even their approach to cooperative breeding is unusually complex. Some groups have multiple breeding males and females, and all of a group’s breeding females lay their eggs in a single nest. Each female destroys any eggs that are present before she begins laying, resulting in the demise of more than one-third of the total eggs laid in joint nests. Once all the females have started laying their own eggs, their destructive behavior stops and they remove the debris to a nearby tree. There each egg is gradually eaten by several individuals—often including the female who laid it. Birds that help at nests but don’t get to breed often go out looking for breeding vacancies in other groups, up to about 10 miles away.
Acorn Woodpeckers excavate multiple cavities, any one of which may be used for nesting (the rest are used for nocturnal roosting). They dig cavities in dead or living limbs, large or small, either in the granary (storage) tree or any other large tree. The woodpeckers reuse nest holes for many years. The cavity is usually about 6 inches in diameter, and it may be 8 inches to more than 2 feet deep. Acorn Woodpeckers do not build a nest within the cavity, but during the digging process a layer of fresh wood chips usually accumulates on the bottom. They replenish the chips throughout the nesting period by pecking away at the cavity walls. 3 to 6 eggs are laid, 1 to 2 broods are raised per year, incubation is done by both parents at first and then their helpers in the family group, and incubation period lasts around 11 to 14 days. Young are fed by both the parents and their helpers in the group, and they leave the nest at about 30 to 32 days.
Distribution and Habitat[]
Acorn Woodpeckers live year-round in oak and pine-oak woodlands of western Oregon, California, and the Southwest through Mexico and Central America. They also live in other habitats with oaks present or nearby, including streamside forests, Douglas-fir forests, redwood forests, tropical hardwood forests, suburban areas, and urban parks. Though found as low as sea level, they are more common in mountains, ranging up to the elevation limit of oak trees.