Conservancy Times: Acorn woodpeckers common on Catalina, but uncommon in lifestyle
The Acorn woodpecker (Melanerpes formicivorus) is a very common bird on Catalina. Unlike so many of the Island’s birds that do their best to blend in, the acorn woodpecker’s unmistakable coloring makes it easy to see and identify. It has a black head, chest, back and wings; a white forehead, throat, belly, and rump, and a bright red cap on top of its head. These woodpeckers are hard to ignore with their loud and varied calls and continuous hammering on all things wood.
As its name suggests, the acorn woodpecker has an affinity for acorns, which come from oaks, which are abundant on Catalina Island. But it eats much more than just acorns, with insects, fruit, sap, seeds, lizards and even eggs from their own species on the menu.
Thousands of trees on Catalina as well as utility poles, fence posts, roof eaves – just about anything that’s wood – have had tens of thousands of marble-sized holes pecked into them. Take a closer look and you’ll see that there’s more to these holes than meets the eye: They’re actually acorn stashes or granaries for the woodpeckers.
Often times, a granary can be in an acorn woodpecker family for multiple generations and may have as many as 50,000 holes. Woodpeckers work tirelessly to protect their stores of acorns. They’ll meticulously check each nut to make sure it fits snugly into its allotted hole.
If it doesn’t fit, the bird will pound it in deeper or move it to find a better storage place. This limits the take of their stock by other animals. Woodpeckers will band together and aggressively fight off any animal with the nerve to raid their stores.
Acorn woodpeckers are also unusual in their communal approach to breeding, nesting and rearing young. Instead of the typical one male/one female scenario, a female acorn woodpecker will breed with one to seven males. When the eggs hatch, the father could be any or all the males.
Since all the males share an affinity for the female and a connection to the nest, they generally all participate in the gathering of food and feeding of the young. Cousins and uncles will join in as well, bringing food to the nest, tending to its structure and upkeep, finding and storing acorns in their granaries and warding off predators.
Family units can be as large as 15 birds, which is another reason they’re easy to see. Sometimes a group of males will breed with more than one female, and the females will both lay their eggs in the same nest.
In order for this multiple-female scenario to work, the eggs need to be laid at almost the same time so the young will be at a similar developmental stage. An egg laid earlier than the other eggs will be set aside.
The family group will keep setting individual eggs aside until all the eggs are laid in rapid succession. Only then will they leave the eggs in the nest for the female, or females, to incubate.
The eggs they take from the nest aren’t just knocked out or thrown away. They’re typically set aside as a source of protein for the group. Nothing is wasted.
Very few bird species behave even a little bit like this. So, while acorn woodpeckers may be easy to spot on Catalina, they’re anything but common.
Alexa Johnson is the Outreach and Naturalist Training specialist for the Catalina Island Conservancy.