Acorn Woodpecker
Melanerpes formicivorus

By Rajiv Jauhari
Featured Photo by Jim Akers/Audubon Photography Awards, downloaded from audubon.netx.net

If you happen to be hiking in a region of California that has oak trees, see if you can spot a granary. I don’t mean a building in which grains are stored by humans. I mean a tree in which Acorn Woodpeckers have created hundreds of holes, and then pushed acorns into the holes. A single granary tree can contain as many as 50,000 holes, each of which is typically filled with an acorn in autumn. Holes are drilled mainly in the winter and are made in dead limbs and thick bark without penetrating the cambium and phloem layers associated with sap. As a result, the holes do not harm living trees. Holes are reused annually. Large granaries are the product of dozens of generations of woodpeckers working in small groups – it has been estimated that a 50,000 hole granary could have taken as many as 100 years to construct.

Acorn Woodpecker, Atascadero, California. Photo by Rick Derevan/Audubon Photography Awards, downloaded from audubon.netx.net.

Almost any dead or living tree with deep dry bark may be used as a granary. Besides trees, Acorn Woodpeckers are also willing to store their food in utility poles, fence posts, wood-sided buildings, undersides of roof tiles and even the occasional automobile radiator. After a group has filled its available granary facility (typically one or two trees per group), it may start filling larger cavities such as abandoned nests and roost holes. In addition to being flexible about where they store food, they are also flexible about the kind of food that they store. Although most of the holes are used for oak acorns, some can be used for almonds, walnuts, hazelnuts, pecans or seeds of pinyon pines.

The ability of Acorn Woodpeckers to store large quantities of food has been confirmed by examples in which the birds used a structure which later collapsed, making the food un-retrievable by the birds, but allowing scientists to count the food items. 62,264 acorns were counted in the door and window casings of an unused house, and 485 pounds of unused acorns apparently stored in a single season were retrieved from a wooden water tank.

In addition to their remarkable food storage methods, Acorn Woodpeckers are also famous for their complicated social system. Family groups hold territories, and young birds stay with their parents for several years and help the parents raise more young. Several individuals of each sex may breed within one family, with up to seven breeding males and three breeding females per group. The oldest Acorn Woodpecker on record was more than 17 years old.

Acorn Woodpecker, adult and juvenile. Photo by Richard Mittleman/Audubon Photography Awards, downloaded from audubon.netx.net.

At least in parts of California, the population of Acorn Woodpeckers has been increasing over the last few decades; these birds are doing well. Their worldwide population has been estimated at 7,500,000. There should be plenty of them to see and admire if you travel to their range.

Although Acorn Woodpeckers are rarely seen in Travis County, there was one observed in Pace Bend Park in 2023. Acorn Woodpeckers can regularly be found in and around the Davis Mountains in Texas. Although Acorn Woodpeckers are rarely seen in Travis County, there was one observed in Pace Bend Park in 2023. In addition to California, Acorn Woodpeckers can regularly be found in and around the Davis Mountains in Texas, and also in parts of New Mexico, Arizona, Oregon, Mexico, Central America and Colombia.

References:
https://birdsoftheworld.org
http://allaboutbirds.org
https://pif.birdconservancy.org/ACAD/Database.aspx