As the days continue to lengthen and the birds outside start ramping up their activities for the breeding season it is time for some of our resident species to start house hunting. A large number of the species that we see at our wintertime feeders will actually be looking for dead, or dying trees that have just the right properties to be attractive as homes. For some, this will mean just the right amount of damage and decay, for others this will mean a reliance upon other species.

The most obvious group of birds to start with is the avian family “Picidae,” otherwise known as the woodpeckers. Here in our area we can expect to find as many as six different species and they range in size from the very small (the downy woodpecker is about 7 inches long) to the very large (the pileated woodpecker is up to 19 inches long; about the size of a crow). All rely on a standing stock of trees that have been outcompeted by nearby trees, or damaged by disease or physical injury.

We humans are compulsive cleaners and we spend a great deal of time, effort and resources grooming our yards. Dead trees are seen as unsightly and downed wood is quickly cleaned up and removed. For woodpeckers, however, standing dead wood is an essential resource. Woodpeckers feed on and around dead portions of trees and they will excavate homes inside other dead portions of trees. Downy woodpeckers can nest in rather small trees, but pileated woodpeckers are going to require much larger trees. The hairy and red-bellied woodpeckers, northern flickers and yellow-bellied sapsuckers will require trees of intermediate size.

If you have been outside at all this past week, then you may have heard the non-vocal territorial drumming performed by downy and hairy woodpeckers. For this, the birds need to find a particular dead branch that is properly cured to be dry, firm and resonant. The birds tap very rapidly and send out their drumming claim across the landscape. Dead wood doesn’t last forever, which means that a fairly constant supply of dead branches is required and the positions of acceptable drumming sites will shift over time.

Housing requires a different type of dead wood. A dead tree, or branch will need to be firm enough to be stable and offer protection, yet decayed just enough to allow for excavation. The birds will typically drill horizontally into the dead wood and then make a 90-degree turn downward to a sufficient depth that will protect the eggs and chicks from predators that might try to reach in and grab them. The larger the species, the deeper the nest cavity must be and (generally) the larger the diameter of the nest tree.

Then, of course, there is foraging. Woodpeckers need a different sort of tree for food; the sort of tree that is decayed and full of insects and insect larvae. With trees like this the birds aren’t necessarily trying to drill holes as much as they are simply trying to uncover food and the larger species have the ability to simply disassemble the trees in question. They simply hack the trees to pieces and often leave large quantities of wood chips on the ground; a sure sign that they have been hard at work searching for food to give to their chicks.

So where do all of these dead trees come from? Well, that last storm back in March was a prime example. Heavy, wet snow piles up on branches and freezes in place. Then high winds put so much stress on the trees that something is bound to give. Sometimes a small branch snaps off a tree and might become a drumming post. Sometimes a large branch breaks off of a large tree and exposes the wood of the inner trunk to infection by various fungi. Perhaps a trunk snaps cleanly, leaving what looks like a telephone pole standing in the forest. Each of these situations eventually offers an opportunity to someone. It’s just a matter of time.

And I haven’t even had the chance to discuss the secondary housing market. Woodpeckers rarely use the same cavity for a second nest, but the abandoned cavities will persist for a time and birds like the eastern bluebird, the tree swallow, the bufflehead, the hooded merganser, the wood duck and the eastern screech owl will happily move in. Sometimes the cavities are used for winter shelter and other times the cavities are used as nesting sites.

The important part to remember here is the fact that once a tree, or a major limb dies, the clock starts ticking. It will have some sort of value to one species or another, but the resource will not last forever. Thus, a constant supply of imperfections must constantly be available and severe winter storms are a great source of damage that can replenish the supply; sort of a stimulus for cavity nesters if you will. If there is a damaged tree in your yard and it isn’t posing any threat to property, consider letting it stand for a while. Someone might find it the thing that they were searching for.

Bill Danielson has been a professional writer and nature photographer for 25 years. He has worked for the National Park Service, the U.S. Forest Service, the Nature Conservancy and the Massachusetts State Parks and he currently teaches high school biology and physics. For more in formation visit his website at www.speakingofnature.com, or head over to Speaking of Nature on Facebook.

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