Love, Acorns, and Drama: The Wild Romances of Riverside’s Favorite Woodpecker
This Valentine’s Day, take a closer look at the Acorn Woodpecker—Riverside’s most social (and scandalous) bird, where love, family, and survival are all part of the story.
With Valentine’s Day just around the corner, love is in the air. Literally, in particular, Riverside’s favorite woodpecker is out and about collecting acorns in anticipation of the mating season. And mating arrangements for Acorn Woodpeckers are the stuff of soap operas. It takes a little background to appreciate the romances of Acorn Woodpeckers and how unusual they are…
Which one is the Acorn Woodpecker?
While it is possible to see up to eight species of woodpeckers in Riverside, the Acorn Woodpecker (Melanerpes formicivorus = “the ant-eating black creeper”) is the most common and obvious. You can see them in any “woodland” situation, provided that oaks are part of the landscape. In Riverside, these range from woody wildlands (e.g., the Santa Ana River Bikeway) to parks (Fairmont Park, Andulka Park, Martha McLean-Anza Narrows Park, Citrus State Historic Park, etc.) to neighborhoods (Wood Streets, Eastside, and other leafy zones) to downtown Riverside (check out the tall palms near the Courthouse).
Acorn Woodpeckers are visually unmistakable. These boldly patterned black birds are often seen creeping on or flying among palm trees and utility poles. Bright white patches on their wings and rump flash as they fly with a characteristic undulating flight of flap-flap-flap-descending glide-flap-flap-flap-descending glide, and so on. Close up (or with binoculars) you can see their clownish faces, black beak and throat, white face, and crazed yellow eyes. Both males and females have a red beanie; females have a black headband around the cap.
Likewise, no other bird sounds like an Acorn Woodpecker. In fact, you are just as likely to first hear Acorn Woodpeckers as to see them. It’s hard to ignore the calls, “Whacka, whacka, whacka!” or “r, r, r, whacka!”. Better yet, listen to the calls on this link: Acorn Woodpecker Sounds, All About Birds, Cornell Lab of Ornithology. The call is so loud and unmistakable that it inspired Walter Lantz to give his cartoon character, “Woody the Woodpecker” a similar voice. (check out Woody Woodpecker laugh) But Walter drew Woody to look more like a Pileated Woodpecker, and that’s another story.
What makes Acorn Woodpeckers special?
Just as Woody is an unconventional woodpecker, so is M. formicivorus. As its Latin name describes, this woodpecker is fond of insects when they are available. And, in accordance with its English name, Acorn Woodpeckers adore, well, acorns. It’s what they do with acorns that set the Acorn Woodpeckers apart from other woodpeckers and all but a handful of bird species. They store surplus acorns so as to have a supply when food is otherwise short. They drill acorn-sized holes in living and dead trees and other available lumber from utility poles and fence posts to, rarely, wooden siding on homes. And we aren’t talking about a few random holes. Acorn Woodpecker “granaries” can consist of thousands or tens of thousands of holes, typically spaced by an inch or so from each other. Even a granary of 50,000 holes is not unusual. I am not aware of any other bird species that stores food for the future in such a dense and organized fashion.
Right now, Riverside’s oak trees are producing acorns by the zillion. The woodpeckers are busy. You might say that a granary represents a lot of work, and you would be right. Creating, maintaining, and filling thousands of holes could be a daunting task. Add to that the effort of defending a cache of goodies against the depredations of squirrels or other birds seeking a snack (e.g., California Scrub Jays). Sounds exhausting for Mom and Pop woodpeckers.
That brings us to the second thing that sets Acorn Woodpeckers apart. It takes a village to get the job done. More frequently than not, Acorn Woodpeckers live in colonies of up to 15 individuals per nest. The little village provides enough bird-power to build, stock, and defend a sizable granary. The vast majority of bird species nest as pairs; complex social structure is the exception.
The specific social structure of the villages is the third way that Acorn Woodpeckers are exceptional. Acorn woodpeckers are cooperative breeders. The typical colony is composed of breeding birds and non-reproductive “helpers”. Genetic studies have revealed that colonies are not random assemblages. The breeding birds associated with a single nest are multiple males (up to 5) who are brothers and fewer females (up to 3) who are sisters but unrelated to the males. Each brother mates with one or more of the sisters; each sister mates with one or more of the brothers. Scientists have a special term for this kind of romantic antics, “polygynandry”. In addition to the breeders, the helpers are the breeder’s children who end up being siblings and cousins. The village is more or less the same as the family.
All members of the group participate in the village’s needs. They build and maintain the single nest, feed the nestlings, working on the family granaries (larger groups maintain more than one granary), and defending their territory from acorn robbers and members of other family groups.
As you enjoy Valentine’s Day on Friday, remember the Acorn Woodpecker’s love life, a life in which food, fraternization, and family ties are intertwined.
Dunne, P. 2006. Pete Dunne’s Essential Field Guide Companion. Houghton Mifflin Company, Boston.
Ehrlich, P. R. et al. 1988. The Birder’s Handbook. Simon & Schuster, New York.
Garrett, K. L. et al. 2012. Birds of Southern California. R. W. Morse Company. Olympia, Washington.
Haydock, J. et al. 2001. Shared parentage and incest avoidance in the cooperatively breeding acorn woodpecker. Molecular Ecology 10:1515-1525.
Koenig, W. D. and R. L. Mumme. 1987. Population Ecology of the Cooperatively Breeding Acorn Woodpecker. Princeton University Press. Princeton, N.j.
McRoberts, M. H. and B. R. McRoberts. 1976. Social Organization and Behavior of the Acorn Woodpecker in Central Coastal California. Ornithological Monographs 21:1-115.
Norm Ellstrand is an emeritus Distinguished Professor of Genetics and former Director of the California Agriculture and Food Enterprise at the University of California Riverside.
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