When it comes to providing nesting boxes for eastern bluebirds, choosing the right size is important for the birds’ comfort and success in raising young. Here are some quick answers on recommended nest box dimensions for this species:
What are the standard nest box dimensions for eastern bluebirds?
The recommended interior dimensions for an eastern bluebird nest box are:
- Floor: 4 x 4 inches minimum (5 x 5 inches is better)
- Depth: 8-12 inches
- Height: 8-12 inches
- Entrance Hole: 1.5 inches diameter located 5-6 inches above floor
Why are these nest box dimensions recommended?
These nest box dimensions are well-suited for eastern bluebirds for the following reasons:
- The 4×4 inch floor gives ample room for the nest cup and clutch of 4-5 eggs. The 5×5 inch floor provides even more room.
- The 8-12 inch depth and height allows the adult birds adequate space to brood the chicks.
- The 1.5 inch entrance hole is ideal for eastern bluebirds. It’s large enough for adults to pass through but small enough to exclude larger cavity nesters.
- Locating the entrance hole 5-6 inches above the floor helps deter predators.
How much interior space do eastern bluebirds need?
Eastern bluebirds do not require a lot of interior space. Here are the key considerations:
- The female builds a nest cup about 2.5 inches tall and 4 inches in diameter.
- A clutch is usually 4-5 pale blue eggs about 0.8 inches long.
- The chicks are quite small after hatching, starting out weighing just 0.6 ounces.
- As the chicks grow, the female sits in the nest much of the time, so adequate overhead space is key.
Given the small size of the chicks, a 4×4 inch floor and 8 inch interior height provides sufficient room. The extra space of a 5×5 floor and 12 inch height gives the chicks more room to move as they grow.
What are the ideal exterior dimensions?
For the exterior nest box dimensions, wider and deeper is better. Here are some guidelines:
- Width: 8-12 inches
- Depth: 12-14 inches deep
- Height: 14-18 inches tall
- Overhang roof: 2-4 inches overhang on front
The wider dimensions give insulation from temperature extremes. The overhang roof protects the entrance from wind-driven rain.
What are the recommended construction materials?
Eastern bluebirds will nest in boxes made from a variety of materials. Some suitable options include:
- Untreated pine, cedar or fir lumber – at least 3/4 inch thick
- Marine plywood – at least 1/2 inch thick
- Cedar shingles
- PVC plastic
- Composite lumber made for outdoors use
The key is to choose decay-resistant materials that will hold up through years of exposure to weather. Also, avoid materials like pressure treated lumber that could leach chemicals.
Where should I mount the nest box?
To attract nesting eastern bluebirds, mount the box in the right location:
- Place boxes 5-10 feet off the ground facing away from prevailing winds and intense afternoon sun.
- Choose an open area with sparse vegetation and perches such as fence posts nearby.
- Eastern bluebirds favor habitats like meadows, pastures, and open woodland edges.
- Space multiple boxes 30-100 yards apart to provide adequate foraging area.
When is the ideal time to put up nest boxes for eastern bluebirds?
To prepare for the breeding season, erect nest boxes from late fall through winter. This timing allows eastern bluebirds to select their nest sites in early spring. Some tips include:
- Late fall or winter – Decide on locations and mount nest boxes.
- January/February – Prior to breeding season, clean out old nests from boxes.
- March/April – Bluebirds arrive and begin checking out nest sites.
- May – Females build nests and lays eggs.
- June/July – Nestlings hatch and fledge.
Having nest boxes up 4-6 months prior to breeding season allows bluebirds sufficient time to find and select their preferred cavity.
How can I discourage house sparrows from using the nest box?
To prevent invasive house sparrows from occupying eastern bluebird boxes, some deterrents include:
- Ensure the entrance hole is no larger than 1.5 inches in diameter.
- Use a box design with the entrance hole on the front side rather than the top.
- Line the bottom edges inside the box with wire mesh 1/4 inch hardware cloth.
- Coat the inside of the box with vegetable oil to prevent nest attachment.
- Place plastic PVC tubes over entrance holes during the off-season.
It also helps to clean out old nests after each season. House sparrows are less likely to use boxes that don’t contain old nest material.
Conclusion
In summary, well-constructed eastern bluebird nest boxes with dimensions around 5x5x12 inches placed in appropriate open habitat provides critical breeding opportunities for this beautiful songbird. Following research-based recommendations on design, placement and seasonal timing will help attract bluebird pairs successfully raise healthy clutches year after year.
