Acorn Woodpeckers of the Santa Cruz Sandhills

Photo credit: CALM Zoo, Bakersfield, CA

What do acorn woodpeckers and elephant seals have in common?

Both species live in highly social groups with similar behaviors! Imagine a TV miniseries with territorial inheritance and bitter relationships within the family unit. Succession, inheritance, and betrayal, oh my!

Acorn woodpeckers (Melanerpes formicivorus), is a species that lives in groups of up to 15 individuals (multiple generations) that cooperatively breed and raise young in a single shared nest cavity. It's called a polygynandrous breeding core, with non-breeding helpers of both sexes. Elephant seal behavior is similar, they are also highly territorial.

A group can have multiple males that are related to each other (some mix of brothers, fathers, sons, uncles, or nephews), all mating with multiple females that are related to each other (sisters, mothers, daughters, aunts, or nieces). Also similar to elephant seals, the males fight over the group’s females. Female breeders sometimes toss each other’s eggs out of the nest. (Oops, my bad!) 

Biologists think the young birds learn who their brothers and sisters are by remembering who is in the nest with them and identify their parents and adult siblings by noting who feeds them. Triadic awareness is thought to be a characteristic of ravens as well."  --Bay Nature article

​Let’s look at their habitat:

• A group’s territory includes one or more trees with holes for roosting and nesting.
• “Granaries” are the hollowed out holes for acorn storage (they eat the insects inside first).
• They store acorns as backup for those days when there are no insects. 
• Acorn woodpeckers acrobatically catch insects in the air. 
• As the acorns dry out and shrink, the woodpeckers move them to smaller holes so that other animals can’t steal them.

According to Bay Nature, "It takes 20 minutes for a woodpecker to make one granary hole, and a woodpecker group needs at least a thousand holes to survive." Many visitors to our parks will share a story of the woodpeckers long tongue that serves not only to place food in a tree hole, but also "cushions" or "protects" the brain.

A newer study challenges the bird's impact related to head banging.
"Contrary to popular belief, woodpeckers don’t protect their brains when head banging trees. Some hypothesized its spongy skull bone could act as an airbag, whereas others proposed its elongated tongue could be a seatbelt for the brain." Science Advisor / Current Biology (2022) and Audubon Society (2022)

The study shows adding shock absorption wouldn’t actually help protect the birds’ brains. If its head absorbed part of the impact, the bird couldn’t exert as large a force —meaning the woodpecker would peck less wood.  See the video below.

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Fun Facts for Kids

• They stash a lot of snacks! They gather delicious nuts from oak trees and store them in holes they chip out of trees. But they don’t only eat acorns; they also snack on insects, fruits, and other seeds! 
• They can also recognize individuals they live with and have their own unique calls.
• They communicate with each other using a variety of sounds, including laughs, chats, and drumming on trees!

Acorn Woodpecker drawing

Photo: F. Van Meter