Love nests for native birds
How to provide cozy homes for native cavity-nesting songbirds
Native wren feeding young at nest in natural tree cavity. All photos by Carolyn Masson unless otherwise stated.
If you build it, they will come!
If you live in the city or the suburbs in North America, you can help native birds by customizing the entrance holes on your birdhouses. Decorative birdhouses are often made without native birds in mind, and cannot successfully be used by them. Native songbirds like violet-green swallows, tree swallows, chickadees, nuthatches, and some wren species are cavity-nesters, requiring tree cavities, or in their absence, birdhouses (nestboxes) to nest in. As breeding season begins, these birds struggle to find suitable nesting sites for raising their young, crucial to the survival of their species.
The competition
Without question the most deplorable event in the history of American ornithology was the introduction of the English Sparrow. —W.L. Dawson, The Birds of Ohio, 1903.
Invasive English house sparrow (male). Photo: Matt Brown.
Native songbirds face fierce competition for nesting cavities from two notorious invaders: English house sparrows (Passer domesticus) and European starlings (Sturnus vulgaris). Both species were introduced to North America in the 1800s. House sparrows are the little brown birds that take handouts at sidewalk cafes and descend upon your feeders in droves. You may think they’re cute, but house sparrows, along with starlings, have spread throughout the continent, out-competing and displacing native cavity-nesting birds. Unless you live in a natural area or have taken measures to deter house sparrows, they are likely nesting in your yard or under your eaves. They are now one of the most abundant songbirds on the continent, and the most widely dispersed in the world. Their effect on native songbird populations and biodiversity has been devastating.
How you can help
Many of the birdhouses that people have in their yards are dangerous for native songbirds because the entrance holes are big enough to allow house sparrows and starlings to get in, aggressively ousting native birds and even killing them on the nest. Here are two ways to customize the entrance holes to keep invaders out (you can also watch the video at the end of this article):
The simplest solution: the small round hole (1 and 1/8”):
Nestbox with round metal hole cover, available at Wild Birds Unlimited and Lee Valley.
Note position of nestbox under the eaves of a house to prevent predator access.
For small native songbirds, simply make sure that the round entrance hole is exactly 1 and 1/8 inches in diameter. This will allow chickadees, some nuthatches, Bewick’s wrens, and other small native cavity-nesters, but will exclude the bulkier invasive house sparrows and starlings. This solution, however, does not work for native swallows (see below).
If the existing entrance on your nestbox is bigger than 1 and 1/8 inches, you can retrofit it with a block of wood with the right size hole. The extra depth provided by a block over the entrance hole is beneficial, as it makes it harder for predators to reach inside. You can also buy 1 and 1/8 inch metal rings at some bird stores. Keep an eye on the entrance hole if it is made of wood. If house sparrows or squirrels widen the entrance, they will oust—and possibly kill—any native birds that have set up house there.
For keeners: the oval entrance hole for swallows:
Oval hole cover. Must be made out of hardwood, plastic wood, or metal to be effective.
If you would like to provide much-needed nesting habitat for native violet-green swallows (Tachycineta thalassina) and tree swallows (Tachycineta bicolor), you’ll need to work a little harder, but the results will be worth the effort. In response to the invasion of English house sparrows, innovators have come up with the oval entrance hole. Swallows can just manage to squeeze through, but house sparrows can’t. The oval must be exactly 7/8 inch high and at least 1.5 inches wide for violet-green swallows.
If you have tree swallows in your neighbourhood, make the oval slightly larger, at 15/16 inch high but no bigger, or house sparrows will get in.
Native violet-green swallow. Photo: Todd Carnahan.
For swallows, place the nestbox in an open area with clear access (with no trees or shrubs near entrance). Smaller native birds will appreciate these boxes too, so if you want to reserve them for swallows, block the entrance until you notice swallows returning from their spring migration, or offer more nestboxes.
For hole covers, use hardwood, plastic wood, or metal if possible. House sparrows will chip at the hole in an attempt to enlarge it. It happens quickly, so you'll need to be vigilant. You can use black paint or a permanent marker to blacken the edges of the hole. If the black disappears, you'll know that an invader has enlarged the entrance. Bonus: the dark edges make the hole more noticeable to potential native nesters, too.
Checklist for suitable nestboxes
➢ Entrance hole is size-specific for the kind of bird you’d like to attract (must be unsuitable for invasive house sparrows and starlings)
Swallow nestbox with oval entrance, overhanging roof, ventilation, 5.5 x 5.5” floor, and opening side panel for cleaning.
➢ No perch (native birds do not need them & perches make landing more difficult for them; also, perches allow invaders to harass birds or reach inside)
➢ Adequate floor area for the species you’re attracting (approximately 5”x 5.5” for swallows; 4”x 4” for smaller songbirds)
➢ Waterproof, with good ventilation and drainage, and an opening front or side panel for cleaning in the fall
➢ Sturdy, made of untreated, durable cedar or pine (do not paint the inside), with an entrance hole cover made of hardwood, plastic wood, or metal
➢ Extended roof to deter predators (or place nestbox directly under an overhanging roof of a building)
➢ Location inaccessible to predators, e.g., attached to your house, generally not on a tree or fence
It is better to provide no nestbox at all
than to provide one that breeds house sparrows.
Resources
Retrofitting an existing birdhouse with an oval entrance hole-cover:
➢Video instructions on making oval entrance hole-covers.
The Rodins may also do house visits and provide nestboxes: 250.812.6461; swallows@shaw.ca. See also this article.
➢Entrance hole protectors made of metal and wood (softwood, unfortunately) are available at Wild Birds Unlimited on Shelbourne Street in Victoria and at Lee Valley. You can use the softwood ones as templates to make hole covers out of hardwood or plastic wood.
➢Fraser Valley Birding article on oval entrance holes (but please use the measurements provided in my article)
Nestboxes & native birds:
➢Cornell University provides excellent resources, including tips on nestbox placement; bird identification; managing invasive species; dealing with predators
➢Infographic: features of a good birdhouse
➢Nestbox designs and tips at Nestbox Builder
Invasive English house sparrows and European starlings:
➢Bluebird site showing damage caused by house sparrows (warning: graphic images)
➢Cornell University page about managing invasive birds
Bring Back the Bluebirds project:
➢The Garry Oak Ecosystems Recovery Team (GOERT) and partners launched their five-year Bring Back the Bluebirds project in 2012 to re-introduce extirpated western bluebirds to the Salish Sea region. Since 2017, the Cowichan Valley Naturalists' Society (CVNS) has taken over the project lead and has transitioned to a mostly volunteer driven initiative. For more information on the project, visit www.cowichanbluebird.ca.
To report a western bluebird sighting or receive Bring Back the Bluebird Project updates, contact cowichanbluebird@gmail.com or call 250-710-5618. Find CVNS on Facebook at www.facebook.com/CowValleyNaturalists.
Please contact CVNS before providing bluebird boxes. They must be placed in natural areas where there are no house sparrows or cats and need to be monitored regularly.
Download a printable PDF version of this article.
© Carolyn Masson | Victoria, BC | CANADA | May 2019 | carolyn@carolynmasson.com
Carolyn Masson shares some tips on how to provide useful habitat for native birds with the right size hole for your birdhouses. Watch to the end to see a real chickadee nest!