• This male eastern bluebird is perched at the entrance to Box 21 and clearly has a nest full of chicks that are hungrily waiting for food. For the Recorder/Bill Danielson

For the Recorder
Published: 6/13/2021 3:00:11 PM

Ever since I rented my first house in 1992, I have made sure that I put out nest boxes. My primary focus has always been bluebirds, but I quickly learned that there are other species of birds that will show tremendous interest in such a valuable resource. Tree swallows, house wrens and even black-capped chickadees will all use nest boxes if they are available. This is because all of the species that I have mentioned are dedicated cavity nesters.

Natural cavities are usually the result of the decay of wood that allows woodpeckers to excavate nest holes, or the “natural” decay of wood at the site of a broken branch. Chickadees are little excavators and will often make their own cavities, but the bluebirds, swallows and wrens must rely on “found” cavities. Wrens may show a little flexibility and will nest in stone walls and even piles of firewood, but the bluebirds and swallows really are at the mercy of the random availability of cavities that they do not need to make.

For the last 16 years, I have been in the same house that sits on 6 acres of land and contains a mixture of lawns, trees, a wet meadow and genuine forest. The area adjacent to my house is mowed weekly and, to the west, there is a large treeless patch of grasses that I mow once every three or four weeks. It is there, right at the very center of this “field” that I planted a nest box that I identify as “Box 21.”

Why number 21? Well, I had some old tree tags leftover from my graduate research and the first series that I could start with a number one was 21. So, each of the boxes that I have put out had a circular aluminum tag (similar to a dog license tag) with a number stamped into it. The grassy field was the most obvious place to put my first nest box, so Box 21 was “planted” there and there has been a box in that spot ever since. After 16 years, however, I am currently on the third version of Box 21; the others needing replacement after a while. What is really interesting about this box is the variety of different species that have used it over the years.

I am currently reading a wonderful book by Bernd Heinrich called “White Feathers: The Nesting Lives of Tree Swallows.” In this book, Heinrich follows the annual arrival of tree swallows in an open clearing in the woods of Maine and he definitely observed tremendous site tenacity from the tree swallows that nested there. Year after year, the same pair returned to his land and nested in the same box; this despite the fact that there were a large number of boxes to choose from.

While I have not made observations at the same level of detail as Heinrich has (a level that one reviewer lovingly described as fanatical) I do have year-to-year records of who has lived in each of the nest boxes that I have put out around my house. Of particular interest to me is the fact that, unlike Heinrich’s boxes, which have the same tenants year after year, I have had a constantly rotating clientele.

Consider just the past five years. In 2017, a pair of bluebirds nested in Box 21. In 2018, it was a pair of tree swallows that claimed it. Then in 2019 and 2020, I had house wrens. I have to admit that, although house wrens are delightful birds, I was a little disappointed that they had moved in. Box 21 is in prime bluebird habitat and the wrens could easily have lived somewhere else. There were plenty of other boxes for them, but that might be a story for another day.

This year, there was some question about who would successfully claim and defend Box 21, but in the end, it was a pair of bluebirds again. Last week, when I walked over to check the status of the nest, I encountered the female bluebird perched atop the post with a beak full of food. When I peeked into the nest, I discovered five extremely healthy-looking chicks with eyes open and an “uh-oh” look on their faces. I quickly closed the box and retreated so as not to disturb them and I am determined to set up shop in front of the box with my camera so I can capture more photos like the one I have provided for this column. The variety of insect prey that is delivered to the chicks is what interests me the most.

So, now I am left with this really interesting question: why have different birds used the same box in different years? If I had this question in my mind 16 years ago, I might have devised an observation and data collection plan that might have made such a question easier to answer. What I do have access to is a large collection of random observations that I did manage to compulsively record by date. There are years of raw data there, complete with complementary meteorological data. All I have to do is try to make sense of it. That, by the way, is the far-less glamorous part of ecological research — the desk work.

Well, it appears as though I have run out of room long before I have run out of material. I have to end this particular column having only scratched the surface of this wonderfully engaging topic, but I don’t have to stop writing about it. Next week and the week thereafter can provide room for an extended series. After all, each year has its own story to tell and there is also more than one nest box to think about. So, let’s end with this question: If several species are vying for it, then who wins and why? I have a feeling that the weather may play an important role.

Bill Danielson has been a professional writer and nature photographer for 24 years. He has worked for the National Park Service, the U.S. Forest Service and Massachusetts State Parks and currently teaches high school biology and physics. Visit for more information, or go to Speaking of Nature on Facebook.


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