Invading House Sparrow Threatens Bluebird
For the past few years I have used this column to focus on several invasive plant and insect species that are having a negative impact on our forests and fields. These invaders thrive here, in part because they inhabit an environment free of natural predators found in the region where they originally evolved.
Take a summer walk in the woods or along a road and you’ll find insects native to lands far away devouring the leaves of our trees. You’ll also find fast-growing invasive plant species out-competing our native plants for sunlight and soil, choking them out and taking over the landscape.
When we think of invasive species we don’t usually think of birds, especially birds that have been in our country for more than a century and are seemingly part of the natural order of avian species inhabiting our lands. But there are two bird species in our region worthy of invader status – the European starling and the house sparrow.
Also known as the English sparrow, the house sparrow was introduced from Europe in 1851 because it was considered pretty and useful in controlling insects. Since then they have spread throughout most of North America and now inhabit every continent except Antarctica.
House sparrows typically build their nests in holes of buildings and other structures with openings such as streetlights, open roofs and sheds or even signs and overhanging fixtures that hold street lights. They are aggressive birds and will displace some birds who have already occupied a nest box, wreaking havoc on the lives of smaller birds nesting in tree cavities and man-made structures. In particular, they make it very difficult for bluebirds to successfully nest without frequent nest box monitoring by humans.
House sparrows are not usually found in forests or grassland habitats. But, due to their preference for nesting on human-made structures, they are easily found in cities, towns, suburbs and near farms with barns for livestock.
The house sparrow will visit bird feeders and eat wild foods such as ragweed and other grasses, as well as insects, which they also feed to their young. They catch insects in the air or by pouncing on them on the ground. In cities, they have adapted to thrive on the crumbs left behind by humans, including pizza crusts.
When occupying a tree cavity or nesting box, the house sparrow will fill it almost to the top with course, dried vegetation and then finer materials such as string, grass and feathers for lining the nest. If they find a bluebird already occupying a nest box, the house sparrow has been known to kill the young and even the nesting adult by pecking it. They then build their own nest on top of the dead bluebird’s nest.
There is nothing quite so disheartening as to see a house sparrow enter a nest box you know is already occupied by a bluebird pair. I have tried to keep this undaunted invader from taking over the bluebird nest boxes I keep in our backyard and, so far, have been mostly successful.
My bluebird nesting boxes are the older, traditional-style wood box with a 1.5-inch hole for the bluebird to enter and exit, a slanted roof and a box 9 inches tall by 4 inches wide. I make sure to clean them out in late winter and keep a watchful eye for when the bluebirds return, as well as for any house sparrows in the area. I have had success with bluebirds and most years a pair will have two and sometimes three broods.
The struggle between bluebirds and house sparrows can render gruesome results in which the bluebird always loses. Bluebird populations only recently seem to be rebounding from sharp declines, and one major reason is the nesting boxes placed by landowners; yet in these same nesting boxes the bluebirds become targets for house sparrows. There are ways to mitigate the impact of house sparrows on bluebirds, including disrupting the nest should sparrows take up residence in a box meant for bluebirds. If a house sparrow is causing concern for your native nesting birds, an online search will offer options for handling the problem.
Ingenuity may also provide a solution. Some of my bluebird nest boxes are getting a bit old and tattered, so I’ve been researching options. This coming nesting season, I plan to change the boxes out for styles designed specifically to deter house sparrows.
I found two designs online offered by Duncraft worth considering. One design uses a 1.5-inch slot at the top of the box instead of the traditional 1.5-inch hole. According to research done at the University of Kentucky, house sparrows don’t like a slotted entrance.
Another new design is for a slanted box, tapering to a narrow edge at the bottom. Again, this design is supposed to deter house sparrows who prefer a square area for their large nest instead of a restricted nesting area, which doesn’t seem to bother bluebirds.
Duncraft is easy to find online by going to https://www.duncraft.com and clicking on the Houses tab and Bluebird Houses. We’ll see how well these designs work for the bluebirds who frequent my property, as well how effective they are for deterring the invasive house sparrow.
We live in a beautiful region called The Last Green Valley, and, despite the environmental challenges of invasive plants, insects, and even the house sparrow, it remains a part of the world that holds my heart. I hope you’ll join me and others as we look to mitigate the effect of invasive species and help us care for, enjoy and pass on this place we call home.
Bill Reid is the chief ranger of The Last Green Valley National Heritage Corridor and has lived in the region for more than 35 years. He can be reached at
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