What’s in the box? A peek inside bird nesting boxes, where to find them, and why they matter

WRITTEN BY AISLINN SARNACKI

Each spring, I visit the bird nesting boxes that are posted throughout the meadows at Fields Pond Audubon Center in Holden. Standing at a distance, I wait for bluebirds to carry caterpillars to their hatchlings. Their azure feathers shine in the warm sunlight. I could spend hours watching them tend their nest.

For me, this is a rite of spring, something to look forward to. While most bird nests are tucked away in trees or shrubbery, bird nesting boxes — also called birdhouses — are out in the open, offering people the opportunity to view wild birds as they pair up and care for their young.

Yet I recently realized that while I enjoyed visiting nesting boxes, I actually knew little about them. And I’m not alone.

“It’s so misunderstood why we put them out,” said Doug Hitchcox, staff naturalist at the Maine Audubon.

Here’s the long story short: Many bird species nest in tree cavities, Hitchcox explained. These cavities are often formed from holes drilled by woodpeckers in dead or dying trees, which become scarce in well-developed areas.

“One thing humans are really good at removing from the landscape are dead trees,” Hitchcox said. “They worry about them falling on their houses or cars.”

Fewer rotting trees means fewer tree cavities for birds to nest in. Nesting boxes serve as an alternative.

BIRD HOUSING 101

In Maine, the bird species that most often use nesting boxes include eastern bluebirds, tree swallows, house wrens, black-capped chickadees, titmice, and nuthatches. In addition, certain ducks such as the wood ducks, common golden-eyes, and hooded mergansers will use larger nesting boxes that are placed near water. Owls and woodpeckers will also take up residence in birdhouses on occasion, if they are the correct size.

Hitchcox said that putting out a nesting box on your property is a great way to observe some of your resident birds while providing them suitable places to nest.

“Right up there with putting out bird feeders, I think it’s a great thing that people can do locally that will at least increase their appreciation of the birds,” he said, adding that a birdhouse might even be more beneficial to the birds than a feeder because birds often have plenty of natural food on the landscape.

Simple in design, nesting boxes are just what their name implies — wooden boxes that birds can enter through a hole to build their nest inside. These types of birdhouses often have a wall that can open for easy cleaning, plus drainage in the floor.

“Just drilling a few holes in the bottom corners allows moisture to get out,” Hitchcox said. “That often seems to be an oversight, and unfortunately, rain can get in sometimes.”

The roof is usually slanted to allow water to roll off of it, and the boxes are often placed on posts to hold them above the ground and out of the reach of predators.

The entrance hole of a bird nesting box is sized to fit a specific species. So, if placing one on a property, you can select a box for a species that you’ve already seen in the area. Or you select a box for a species you hope to attract to that area. Or you could simply erect a bluebird nesting box, Hitchcox said. That seems to be suitable for many cavity-nesting species.

Shops and online retailers sell premade nesting boxes, or you can build your own. It’s an entry-level craft, with detailed instructions available online. The Cornell Lab of Ornithology website, birds.cornell.edu, is a great place to learn more about constructing your own and finding a good place to put it.

THE SECRET LIFE OF BIRDS

Nesting boxes can come with a bit of drama. House wrens, for example, often will claim multiple boxes and won’t allow other birds to move in.

“They build all these dummy nests,” Hitchcox said. “The male will just shove sticks in every cavity he can find.”

House wrens are native to Maine. But nesting boxes can also attract a non-native, invasive species, such as the house sparrow, which Hitchcox said is fairly aggressive. He suggests people cover up their nesting box entrances if that species tries to move in.

Hitchcox also advises that people keep house cats away from nesting boxes and feeders. Otherwise, your nesting birds may not survive.

Natural predators such as racoons and squirrels will sometimes raid nests, he warned. Predator guards are devices that can help prevent this from happening to your nesting box, but it’s a personal choice whether or not you want to invest in that.

“When you put out a nesting box, you’re inviting nature to happen in your backyard,” Hitchcox said. “And nature isn’t always kind.”

WHERE TO OBSERVE NESTING BOXES

If looking for bird nesting boxes to visit in Maine, you don’t have to travel far. Many parks and preserves erect nesting boxes to attract different species and make them easier to view.

Maine Audubon, for example, has placed dozens of nesting boxes at its nature centers at Field Pond in Holden and Gilsland Farm in Falmouth. Trail networks at both preserves allow you to walk close to the boxes for easy observation.

The fields at Hirundo Wildlife Refuge in Alton are peppered with nesting boxes as well. In fact, the name “Hirundo” is Latin for swallow — a nod to the birds who use the boxes.

Bird nesting boxes are often placed in fields and along the edges of marshes. So if you know of a preserve or park with these habitats, keep your eyes peeled. For example, nesting boxes can be found in the fields of Curtis Farm Preserve in Harpswell and Law Farm in Dover-Foxcroft.

Nesting boxes can also be found along the Downeast Audubon Bluebird Trail, which was started in 2008 by Lynn Havsall. The most recent numbers, posted in 2022, show the trail at 443 birdhouses in 129 locations throughout Hancock County.

Sites of the trail include Blue Hill Mountain in Blue Hill, Great Pond Mountain Wildlands in Orland, Cooper Farm in Sedgwick, Jordan Homestead Preserve in Ellsworth, Furth Field in Surry, and many more. For more information, visit downeastaudubon.org.