Today we have a batch of lovely photos about acorn woodpeckers (and a few of their relatives) courtesy of UC Davis ecologist Susan Harrison. Susan’s captions are indented, and you can enlarge the photos by clicking on them.
Acorn Woodpeckers: One to three brides for up to seven brothers
Acorn Woodpeckers (Melanerpes formicivorus) have a rare social system called polygynandry in which multiple parents of both sexes rear offspring collectively. These co-breeders also cooperate to defend a group territory and the all-important granary in which they store acorns for the winter. An early ornithologist dubbed them “communists,” and long-term field and genetic studies more recently discovered the structure of their social groups. Up to seven males, often brothers, breed with one to three females that are often sisters and unrelated to the males. Offspring hang around and help at the nest, but when a breeding individual dies in a nearby territory, the erstwhile helpers form single-sex coalitions and initiate dramatic battles to fill the vacancy.
Recently I observed a battle or skirmish among about 15 Acorn Woodpeckers. The main tactics were chasing, swooping, and making a continual racket. While it may have been a territorial dispute, it had a slightly laid-back quality that made me wonder if it was simply the sorting out of who would mate with whom.
Acorn Woodpeckers chasing, swooping and yelling:
They also did a behavior called the “waka display” in which the bird perches vertically and spreads its wings while calling waka-waka-waka. This can be a greeting, assembly call, or display of dominance.
Doing the waka display:
Those studying Acorn Woodpeckers, led for many decades by Dr. Walter Koenig, have concluded that the granary is the key to the bird’s remarkable social adaptations. Trees with thousands of laboriously drilled acorn-shaped holes, which allow the birds to survive winters well fed, are a precious resource that takes a close-knit group to build and defend.
Eating the last of the acorn hoard in spring:
Here are some other birds of the woodpecker tribe that I saw in recent weeks.
Red-breasted Sapsucker (Sphyrapicus ruber), appearing to eat scale insects from the bark of a Madrone (Arbutus menziesii):
Pileated Woodpecker (Dryocopus pileatus), the crow-sized king of the forest:
Thanks for the wonderful photos. I love woodpeckers and am fortunate to have four species visit me regularly, plus on rare occasion, pileateds (an apparently bonded pair fed on my suet blocks and ate sunflower seed over the winter). The red-breated sapsuckers are gorgeous–I wish we had those in south central PA!
Thanks for this! A couple of decades ago when I visited the Big Sur region I was intrigued by the acorns stashed in the trees by those woodpeckers. (I thought it was cool.) At that time Sudden Oak Death (caused by Phytophthora ramorum) was impinging on the region, and the results there were sadly dramatic: entire hillsides of dead trees. I wondered about the fate of the woodpeckers under this circumstances.
What an interesting post! I wonder if acorns ever germinate from inside the holes.
They do. I saw about a dozen little trees sprouting from a fallen granary tree.
Nice informative post! Thanks!
Amazing photos!
Beautiful photos of Acorn Woodpeckers, their granary, and their polygynandrous lifestyle, all succinctly explained. Thank you very much.
Beautiful photos. I especially like the action photos. A pileated woodpecker visits me for a few days each spring on its way elsewhere. The sound it makes pounding on my fence is unmistakable.
Superb pictures; great information. Thanks!
Very interesting natural history information; how neat that the social structure is so closely connected to their unusual food storage habits.
Great photos and interesting commentary.
Awesome!
“Up To Three Brides For Up To Seven Brothers” – someone should make a movie about this! Fascinating!
Fabulous action shots!