All backyard birders understand the importance of birdhouses for providing birds with suitable nesting sites. After nesting season ends, however, roosting boxes—which are different than birdhouses—can be even more critical for birds’ survival. Depending on the bird species and size of the flock, a dozen birds or more may take advantage of a single roosting box to share body heat through cold winter nights. This communal roosting in a sheltered spot greatly improves the birds' chances of surviving harsh weather and sudden freezes.
Birds that frequently use roost boxes include downy woodpeckers, bluebirds, titmice, nuthatches, chickadees, and wrens. Other species, typically smaller birds or other species that use birdhouses, may also take advantage of roosting boxes.
What Is a Roosting Box?
A roosting box is similar to a birdhouse in that it provides shelter for birds. However, unlike birdhouses, roosting boxes are not intended for building nests or raising hatchlings. Instead, a roosting box provides shelter from predators, low temperatures, and poor weather for multiple cavity-nesting birds at once.
Roosting Boxes vs. Birdhouses
At first glance, a roosting box looks very similar to a birdhouse. In fact, many birds will use empty birdhouses for roosting, even though they aren’t ideal. To encourage birds to roost, a well-designed roosting box will have:
- Fewer ventilation and drainage holes to conserve more heat
- An entrance hole near the bottom instead of the top to prevent rising heat loss
- Interior perches to accommodate greater numbers of birds without smothering
- Scored walls or interior mesh to help birds cling and climb safely
- A hinged side, bottom, or top for easy cleaning
- A metal guard around the entrance hole to deter predators
- Larger than typical dimensions to accommodate more birds
- Thicker walls for better insulation in winter
Birders can convert birdhouses into winter roosting boxes by making simple changes to nesting shelters. For example, a birdhouse may be able to have its front panel flipped to move the entrance hole location. Additionally, using sturdy tape to block some of the ventilation and drainage holes can keep the house warmer, and adding wood shavings to the bottom of the house improves insulation for cold weather as well.
Roosting Box Placement
Ideally, roosting boxes should be placed in a sheltered area that's protected from prevailing winter winds. Place it in a south-facing location that gets sunlight during the day, particularly in the late afternoon, which will cause the box to retain the heat for a time and be more attractive to birds. The ideal height for a roost box varies for different bird species, but the box should be mounted on a pole or tree trunk between 6 to 15 feet from the ground. If you mount the box on a pole, use baffles to deter predators and keep unwanted wildlife out of the box.
Encouraging Birds to Roost
There are certain things you can do to make your roost box as attractive and safe as possible for the birds.
- Add a second entrance hole to large roost boxes to help birds exit quickly when they are ready to feed or if they feel threatened.
- Spread a layer of moss or small wood chips to the bottom of the box for better insulation and to make it more comfortable. This will also make cleaning easier.
- Paint the box with non-toxic paint in a dark color to help it retain more solar heat. The interior of the box should not be painted.
- Choose a roost box with an entrance hole appropriately sized for your backyard birds. A hole with a 1 1/2- to 2-inch diameter is perfect for most small birds, while larger holes could encourage starlings to roost, forcing smaller birds to go without shelter.
- Add tape or caulk to the seams of the box to eliminate cracks that will lead to drafts and heat loss. Birds can lower their body temperatures 10 to 15 degrees to conserve energy during winter nights, and even a small draft can become fatal during a cold snap.
- Clean the roost box periodically, removing any buildup of feces, shed feathers, or other debris. Only clean the box when it is not in use, and be sure it is thoroughly dry and ready for birds to use again at night.