The Acorn Woodpecker (Malanerpes formicivorus) is a highly social and colorful character. The red-crown, white forehead and bold black and white patterning on this woodpecker give it a clown-like appearance. Its name is derived from the close association with oak and pine-oak woodlands in which they nest, roost and store food.
While acorns make up a major portion of their diet, this species also feeds on sap, catkins, fruits, seeds and insects. They are a common sight in urban and suburban parks where oak trees are available. They have a unique method of storing acorns in storage trees and man-made structures referred to as “granaries”. Highly social, they live year-round in cohesive social units. In California, Acorn Woodpeckers can live in family groups of up to a dozen or more individuals. Birds living in social units store acorns communally and cooperatively raise young.
Acorn Woodpeckers are well-known for their specialized food storage methods. Insects captured are often stored in crevices. Acorns are stored in oak trees and man-made structures. These storage areas are referred to as “granaries”. An individual granary tree may contain only a few of or as many as 50,000 holes, each of which is typically filled with an acorn in autumn. (Koenig, 1995) Acorn Woodpeckers may have one or more storage trees and will aggressively defend them against acorn-eating competitors such as squirrels, nuthatches and jays. Holes are drilled in the dead limbs and thick bark without penetrating the layers associated with sap production. Consequently, storage holes do not compromise living trees. (Koenig, 1995)
In California, Acorn Woodpeckers breed from April – June. An Acorn Woodpecker group may consist of 1-7 male breeders that compete to mate with 1-3 females. The nest is excavated in a large tree, which may also be a granary tree. Tree cavities are created in both dead and living trees and snags and nest holes are reused for many years. Females typically lay 5 eggs that are incubated for 11 days. Male and females incubate and tend to their young. Non-breeding helpers (young from previous years) often help with incubation and other parental duties. The young leave the nest and take their first flight at approximately 30-32 days after hatching and return to the nest to be fed for several weeks.
Living with Acorn Woodpeckers
Acorn Woodpeckers like many other species are threatened by habitat loss and degradation. Competition for nest cavities by non-native species is an ongoing threat in urbanized areas. Conservation of this species is dependent on the maintenance of functional ecosystems that provide the full range of resources upon which the species depends. These include mature forests with oaks capable of producing large mast crops and places for the woodpeckers to nest, roost, and store mast. (Koenig, 1996)
Because of their social nature, Acorn Woodpeckers rely on a series of vocalizations and “drumming” to communicate with the group. Drumming consists of 2-20 evenly spaced taps and is often executed on specific drumming posts, typically dead limbs with good resonance. Drumming is associated with intra-specific territorial encounters and as a method to attract mates. Drumming is done by both sexes and may occur at any time of the year but is most common in spring. (Koening, 1996) Drumming is also done on telephone poles, buildings and other man-made structures that provide good resonance. (…Often to the dismay of their human neighbors!)
How can I help Acorn Woodpeckers?
- Acorn Woodpeckers would greatly benefit from the preservation of mature oak and pine-oak forest in your own back yard!
- Provide dead limbs and snags for nesting, roosting and granary sites
- Plant an oak tree!
Acorn Woodpeckers are drilling holes in my house. What can I do?
There are several non-lethal ways to deter woodpeckers from using your house as a granary site. We spoke with the experts and here is what they suggest…
- Install black netting secured with 1x firring along the perimeter of the structure the woodpeckers are drilling. The netting should be secured tightly so that when the woodpeckers land on it they bounce off. The surface of the net will make it uncomfortable for the birds to reach the wall to insert acorns and the netting holes are small enough to prevent the woodpeckers from reaching their heads through to drill. (Netting sold at birdbarrier.com)
- Hang battery-powered spiders on your house. These spiders are sound activated and drop down by a string and then climb back up when sound is detected. This movement will frighten off the woodpeckers.
- Place sheet metal over the drilling area. The woodpeckers will not be able to penetrate the metal. (Please note that the resonance produced by the metal may become a favorable drumming post.)
- Place a superficial layer of brick or concrete over the drilling area.
- Provide dead limbs and snags in your yard that can be utilized for nesting and granary sites.
Koenig, Walter D., Peter B. Stacey, Mark T. Stanback and Ronald L. Mumme. 1995. Acorn Woodpecker (Melanerpes formicivorus), The Birds of North America Online. Vol 194 (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology