When it comes to building or buying a birdhouse, one of the most common questions is “Can a birdhouse be too big?”. The short answer is yes, a birdhouse can absolutely be too large for the types of birds you are trying to attract. However, there are a few factors to consider when determining the ideal size for a birdhouse.
In the opening paragraphs, it’s important to cover the basics of birdhouse sizing and explain why size matters when it comes to birdhouses. The main points to touch on are:
- Different bird species prefer different birdhouse dimensions based on their body size and nesting behaviors.
- Birdhouses that are too large may be avoided by small birds or taken over by larger, more aggressive species.
- Oversized birdhouses are more difficult for small birds to keep warm and defend.
- Ideal birdhouse dimensions leave just enough room for the nest while providing protection, shelter, and temperature regulation.
By covering these key facts upfront, the reader will have context for why a birdhouse that is too big can be problematic. It also sets up the discussion for ideal birdhouse sizing.
Ideal Birdhouse Dimensions for Common Backyard Birds
When building or buying a birdhouse, it’s important to match the size to the specific species of birds you want to attract. Here are some common backyard birds and their ideal birdhouse dimensions:
Chickadees
- Floor of base: 4 x 4 inches
- Depth of base: 8 – 10 inches
- Diameter of entrance hole: 1 1/8 inches
- Height above floor to hole: 6 – 8 inches
Nuthatches
- Floor of base: 4 x 4 inches
- Depth of base: 8 – 10 inches
- Diameter of entrance hole: 1 1/4 inches
- Height above floor to hole: 6 – 8 inches
Bluebirds
- Floor of base: 5 x 5 inches
- Depth of base: 8 – 12 inches
- Diameter of entrance hole: 1 1/2 inches
- Height above floor to hole: 6 – 10 inches
Wrens
- Floor of base: 4 x 4 inches
- Depth of base: 6 – 8 inches
- Diameter of entrance hole: 1 – 1 1/4 inches
- Height above floor to hole: 5 – 6 inches
As you can see, these common backyard birds have relatively small ideal birdhouse dimensions. A birdhouse that is much larger than these requirements may discourage these species from nesting.
When is a Birdhouse Too Big?
Now that we’ve covered ideal birdhouse dimensions, let’s discuss at what point a birdhouse becomes too large. Here are a few rules of thumb:
- The floor is over 6×6 inches – This may be too big for many common backyard birds besides bluebirds.
- The depth is over 12 inches – This makes it difficult for smaller birds to keep the interior warm and protect the nest.
- The entrance hole is over 1 1/2 inches – Larger holes allow bigger, more aggressive bird species to take over.
- The height above the floor is over 10 inches – Harder for smaller birds to get in and reach nests/young.
Of course, these numbers may vary slightly depending on the exact species. But in most cases, a birdhouse that exceeds these dimensions will be too large for chickadees, nuthatches, wrens, and other birds of that size.
Here is a table summarizing the maximum recommended dimensions for small birdhouses:
| Feature | Maximum Dimensions for Small Birds |
|---|---|
| Floor of Base | 6 x 6 inches |
| Depth of Base | 12 inches |
| Diameter of Entrance Hole | 1 1/2 inches |
| Height above Floor to Hole | 10 inches |
Birdhouses that significantly exceed these dimensions may be avoided by the target smaller bird species.
Problems with Oversized Birdhouses
Now that we’ve looked at when a birdhouse is considered too large, let’s examine some of the specific issues oversized birdhouses can cause:
Difficulty Regulating Temperature
A birdhouse with a large, cavernous interior is harder for small birds to keep warm. Bird eggs and nestlings are very sensitive to drops in temperature. If the nest area is too large, the adult birds may struggle to keep the interior warm, especially on cold nights.
Increased Predation
Larger birdhouse holes and openings make it easier for predators like squirrels, snakes, and raccoons to access the nest. Smaller dimensions keep out unwanted nest visitors.
Takeovers by Larger Birds
Bigger bird species may claim an oversized birdhouse first, preventing the desired smaller species from using it. Larger birds are often more aggressive and territorial.
Difficulty Defending from Competitors
A diminutive chickadee or wren may have trouble fending off competitive nesting species if the interior space and entrance hole are too big. A tight fit makes the birdhouse easier to defend.
Harder to Maintain Ideal Interior Temperature
As mentioned earlier, a large interior cavity causes issues with temperature regulation. Adult birds can’t keep a sprawling birdhouse warm and cozy for their chicks.
Nestlings Can Wander from Nest
In a giant birdhouse, nestling birds may accidentally wander out of the nest before they are ready to fledge. The close quarters of a properly sized birdhouse helps keep babies in the nest.
Higher Nestling Mortality
The combination of increased chances of hypothermia, predation, and accidently fledging prematurely adds up to higher mortality rates for nestlings in oversized birdhouses.
Difficulty Feeding and Monitoring Young
Parent birds have a harder time feeding nestlings and monitoring the nest if it is very deep or high up in the birdhouse. A compact interior makes parenting easier.
So in summary, excessively large birdhouses lead to issues with temperature regulation, habitat protection, nest defense, and feeding and monitoring young. That’s why an ideal snug fit is key.
Examples of Birds That Use Larger Birdhouses
For some larger bird species, bigger birdhouses are necessary to accommodate their needs:
Woodpeckers
Most woodpeckers nest in dead tree cavities, so they require deep birdhouse interiors to mimic their natural habitat. Floor dimensions of 6×6 inches up to 12×12 inches or more may be suitable, depending on the species.
Barn Owls
These cavity nesters appreciate birdhouses at least 24 inches deep, with entrance holes 5 to 6 inches across. Internal perches should also be provided.
American Kestrels
Kestrel houses need roomy interiors, usually at least 16×16 inches floor space and 16-24 inches high. Multiple nest boxes can be clustered together to form kestrel colonies.
Eastern Screech Owls
Screech owls nest in cavities at least 12 inches across and 14 inches deep. As nocturnal predators, large entry holes up to 6 inches may be acceptable to allow easy nighttime access.
Mallards
Duck houses for mallards measure about 24×24 inches floor space, with ramp access as they cannot use perches or entrance holes. At least 15-20 inches of interior height provides needed overhead space.
So for these larger species, bigger birdhouse proportions are appropriate. But for small songbirds, compact dimensions are ideal.
Tips for Getting the Birdhouse Size Right
Here are some useful tips for making sure your birdhouse is the perfect fit for the target species:
1. Research Appropriate Dimensions
Check multiple references on the ideal entrance hole size, depth, floor dimensions, etc for the species you want to attract. Photos of the bird on the nest also give a sense of fit.
2. Erring on the Small Side is Best
When in doubt, choose the smaller end of the recommended range for hole diameter and interior space. You can always enlarge later if needed.
3. Nest Boxes Can be Clustered
Rather than one large box, consider mounting several appropriate-sized nest boxes in the yard to accommodate more pairs.
4. Monitor and Tweak as Needed
Keep notes on which boxes get used and any issues. Make adjustments to size in future years if certain species don’t seem comfortable.
5. Use Restrictor Plates to Adjust Hole Size
Metal or plastic plates with different diameter holes can be used to easily adjust entrance hole sizes between seasons.
6. Ventilation is Key
Ensure adequate air flow through ventilation holes and gaps, which also assists with temperature regulation.
7. Add Woody Debris and Bedding
Provide small twigs, wood chips, and plant fibers inside to mimic natural nesting substrate. This can shrink an otherwise too-large cavity.
8. Stay Within the Typical Natural Cavity Size Range
Reference cavity dimensions of old woodpecker holes and natural tree hollows that birds would use in the wild.
9. Account for Nest Thickness
Factor in that nest materials will take up 1-4 inches of interior space on all sides.
Following these tips will help you choose and build a properly sized nesting box that backyard birds will actually use.
Conclusion
In summary, birdhouse dimensions truly matter when it comes to attracting cavity nesting birds to your yard. While large birdhouses seem welcoming to our human sensibilities, most smaller bird species strongly prefer snug, cozy spaces that are tailored to their body size. Following the ideal size guidelines for the target species in your region will lead to greater nestbox occupancy and breeding success. Just remember, when it comes to birdhouses, sometimes smaller really is better for your feathered friends.
