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Do Woodpeckers Hurt Trees?

Grantus4504/Wikimedia Commons
Hairy Woodpecker

Springtime woodpecker worries are the focus of this week’s Wildlife Matters, as the Masked Biologist tackles another Curious North question from one of our listeners.

I get questions or concerns pretty frequently about woodpeckers hurting or killing trees, so when I saw this Curious North question, I thought I would try to address Jane Trotter’s concerns. She asks “A Hairy Woodpecker is busily working on a Hemlock tree right outside our bedroom window. The Hemlock appears to be alive and well....so far. Will Hairy’s morning percussions hurt the tree?”

In a word, no, the hammering from that hairy woodpecker shouldn’t do any damage. However, I have a little bit of a grin on my face when I say that, because while it is true, it isn’t the whole truth. You see, woodpeckers rarely do any damage…unless there is already damage going on. Woodpeckers do not eat trees, obviously. They eat wood-boring insects and insect larvae. So, if they are hammering away on a tree, especially in the winter, there is a good chance that the tree is already infested below the bark with some kind of insect. I had a pileated woodpecker tearing into the ancient oak tree in my yard this past winter, and now I can tell you the tree is swarming with carpenter ants, the pileated woodpecker’s food of choice. When you see woodpeckers flaking the bark off of ash trees in winter, it is a reliable reliable indication of emerald ash borer (EAB) infesting an ash.  Community foresters and DNR parks managers use woodpecker as an early warning system to prioritize ash trees for removal before they can fall on someone. Woodpeckers are one of the most important biological control methods of EAB in North America and the most important native predator. They have been observed to remove up to 95% of EAB larvae in some trees. This is helpful as it lowers the number of adult pests that will emerge from these trees, or any infested trees, in the spring to mate and lay the next generation of eggs.

That being said, in my mind, there is one other possibility. This question was submitted during the peak of bird breeding and nesting season. It is possible that this was a male woodpecker who was advertising for a mate, or warning other males to stay clear, and had nothing to do with insects at all. It happens frequently in spring that woodpeckers choose a loud spot to send their advertisements, including metal roofs and flashing on cabins or cottages. If this bird is choosing a hemlock for a “song post” if you will, it might be because it is centrally located, or near its nest cavity, or the largest or tallest tree in the area. Or it may be hollow or have a wood defect that gives it the sound that Mr. Hairy likes.

Time will tell, Jane, whether your tree has parasites. But if it does, the woodpecker is trying to help it, not hurt it, by eating as many insects or larvae as it can. If you are really concerned, you might want to consider calling a tree service or arborist and asking them to come out and evaluate the health of this tree so you can take measures to protect its health. If it was just a lonely woodpecker looking for love, you will probably see the percussion slow and stop from now until early next spring.

So, woodpeckers are truly friends of the forest, not fiends. They serve an important ecological function, and there is room for them in a healthy forested landscape.

Here in the Northwoods, we have a good number of woodpecker species. Two species of special concern, the red-headed and black-backed woodpeckers, are few in number. We have a good number of downy, hairy, and pileated woodpeckers here. We also have Northern flickers and yellow-bellied sapsuckers, which are woodpecker relatives as well.

Striving to make new things familiar and familiar things new, this is the Masked Biologist coming to you from the heart of Wisconsin’s great Northwoods.

The photo above is from Wikimedia Commons, Grantus4504, and can be found online here.

Do you have a question for the Masked Biologist? Submit it below to our Curious North series and it could be featured in an upcoming commentary.


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The Masked Biologist is a weekly commentator on WXPR talking about natural resources and wildlife in the Northwoods. He is anonymous so that he can separate his professional life as a biologist from his personal feelings about the natural world.
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