Monday, March 14, 2022

Adorable Acorn Adorners

While my musings about nature generally focus on southeastern Canada and the northeastern United States, there are times when a subject is far too juicy to ignore even if it’s out of this world, like Japanese satellites made from trees. Back home on our little planet, we have a blind, rainbow-hued marine worm which slices fish in half for the joy of it. This “Bobbitt” worm grows to ten feet long and can paralyze a human with its venom.

Also cool but way less terrifying, a rainforest tree on the island of New Caledonia oozes more nickel than the richest mines are able to yield. Vertebrates are great fun, too. In high school Biology we were taught that the pangolin, an armor-plated, dragon-like beast living in Asia and Africa, was born from an implausible and rather scandalous affair between an armadillo and a globe artichoke. As well we learned about Australians and their platypus, which of course resulted when a duck mated with a muskrat, a practice which is now illegal in
that country. Or at least that’s what I remember from class.

My wife recently called my attention to a bizarre North American woodpecker that glued 38,000 pennies to a Cadillac in 2014. Wait – sorry – that was a family from Indiana who likely got tired of waiting for the cable guy to connect their service. Our bird in question does roughly the same thing, but uses acorns to adorn, top-to-bottom, utility poles, wood siding, fence posts, dead trees and such-like. It ensconces each nut into a hole it drills for that purpose. In fact, a researcher once counted 50,000 such acorns “planted” in a single trunk.

There were a few more nuts than that, but I assume 50,000 was the point at which the scientist either fainted from boredom or their grant ran out. Native to northwest Oregon south along the California coast through much of Mexico and parts of Belize, Guatemala, Nicaragua, Panama and Colombia, the acorn woodpecker (Melanerpes formicivorus) eats a great deal of insects, sap, and nectar. Yet it depends on acorns to such an extent that it breeds in autumn in many areas to take advantage of the high-protein food source.

The peculiar habits of this medium-sized (8.3 inches long and 3.0 ounces on average) bird extend to its social life. For one thing, their mating strategy makes polyamorous folk look downright prudish by comparison. The parental unit, if one can call it that, most often consists of three males and two females. In some cases it can grow to as many as three females and seven males, all mating and raising young in a single large cavity. To further complicate matters, offspring typically remain with parents for several years in the communal nest, helping the parents care for hatchlings and younger youngsters.

The general term for a breeding collective like this is a coalition. Not surprisingly, coalitions are rare in the animal kingdom. Aside from acorn woodpeckers, a few hippie communes back in the late 1960s and early 70s were said to have achieved a measure of collective-family success in the short term. I suspect that the subtle balance of intention, dedication, and ganja which held them together was easily upset when hungry hatchlings came on the scene.

Even community-minded acorn woodpeckers go through an adjustment period at the start of each nesting season. For a time, breeding females will destroy one another’s eggs by turns. Once the moms all begin to lay at the same time, domestic life calms down, although as many as a third of the total eggs are reportedly lost in this way. Maybe the reason this multigenerational love-in works is that each family group, which by the way is aptly termed a bushel of acorn woodpeckers, is too distracted to fight much.

They spend the bulk of their time and energy fetching acorns and artfully affixing them to vertical wooden objects. Individuals take turns guarding the family’s hoard, called a granary, giving an alarm call when pilferers like Steller’s jays and western scrub jays come near. As acorns dry and shrink, they are moved to smaller niches, and thus family members are kept endlessly busy maintaining their granaries. Acorn woodpeckers are also a long-lived species, known to survive up to seventeen years in the wild. In light of that, having moms, dads, Junior, Junior Jr., Junior III and Junior IV all on the nest together makes a little sense. Possibly.

So far I have not found evidence that acorn woodpeckers help plant oak trees but it seems likely, as the birds lose track of their nuts even more so than squirrels do. Studies show that grey squirrels (including the black melanistic subgroup) overlook as many as 10% of the hickory nuts, acorns and walnuts they cache. That’s nothing. The Cornell Lab of Ornithology reports that a family of acorn woodpeckers in Arizona kept depositing acorns into an empty wooden water tank from which they could not retrieve them.

In all, they lost nearly 500 pounds. With such a complex social structure, you’d think someone would have been assigned to inventory control. Given that these fascinating birds live much closer than pangolins or platypuses, seeing them has been added to my bucket list, or in this case a bushel list. I’ll try to have it full of acorns when I arrive.

Paul Hetzler is a former Cornell Cooperative Extension Educator who is grateful to his awesome wife Marie-Line for this topic. And for a bunch of other things too.

Photo at top:  “Acorn Woodpecker with Hoard by Johnath – Own work,” Credit: Wikimedia Commons. 

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Paul Hetzler

Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.

You can read more of his work at PaulHetzlerNature.org or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World




2 Responses

  1. Smitty says:

    Thanks Paul. We saw a lot of these birds in the area south and east of Yosemite last summer. The acorns affixed to trees were inyrresting but I had no idea of those other aspects of their behavior.

  2. Bill Ott says:

    I tried reading some lines to my wife but I was laughing so hard while trying to read that she could not understand me. She thinks I am a nut.

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