Bluebird and Small Cavity Nester Conservation
Sialis - Bluebirds and other small cavity nesters
 
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Nestbox Specifications

One excellent way to help native cavity-nesting birds survive and thrive is to put up a nestbox(es). If are going to make or purchase a nestbox, you can select one specifically designed for the species of bird you want to attract. Different size birds with different habits have different preferences when it comes to entrance holes, interior volume, dimensions, mounting, etc. Note that many bluebirders find that boxes with 1.25" or 1 1/8" hole restrictors on them before an egg is laid are not utilized even by smaller birds like titmice and chickadees.

Here are some commonly accepted birdhouse specifications (some sources disagree, so there may be multiple listings. Also, I do not know how reliable the information is - sometimes misinformation gets propagated). I expect birds are most likely to use a man-made nestbox that approximates natural cavity choices. Note that there are many nestbox styles, each of which have their own pros and cons. There are also many choices of material (wood, PVC, other) and types of predator protection.

If House Sparrows are common in your area, avoid a box with a perch, as it gives House Sparrows an unfair advantage. You should also monitor and maintain the nestbox.

Also see Nestbox Plans, Nestbox Styles - Pros and Cons, Bluebirding Basics, and Top Tips and Tricks for Attracting Bluebirds.

Species
Click on bird name for more info
House
Floor
(Inches)
House
Depth
(Inches)
Hole
Above
Floor
Minimum
Diameter
of Hole
(Inches)
Height
Above
Ground
Bluebird-Eastern
5 x 5"
9"
8-12"?
7"
6-10"?
1.5"-1 & 9/16"
or 1.375" x 2.250" oval
3-6'
4-10'?
6-10'?

Bluebird-Mountain
6 x 6"
5 x 5"?
9"
7"
6-10"?
1 & 9/16"* or 1.375" x 2.250" oval
4-10'
Bluebird-Western
5.5 x 5.5"
9"
8-12"?
7"
6-10"
1 9/16" or 1.375" x 2.250" oval
4-10'
6-10'
Ash-throated Flycatcher
6 x 6"
12"
8-12"?
8"
6-10"
1.75"
1.5"?
3-20'
5-15'?
4-10'?
Barn Owl - box plans (no porch/perch!)
18 x 20"
10 x 18"?
15-18"
4"
elliptical 3" high x 4" wide
8-10'
20-25'
(12-18'?)
Barred Owl
14 x 14"
13 x 15"
26-28"
16"
21-23"?
4"?
6-8"
8"?
15-30'
12-18'?
Bewick's Wren
4 x 4"
6-8"
4-6" or 7"?
1.25 to 1.5"
1"?
6-10'
5-10"?
Black-capped Chickadee
4 x 4"
8"
8-10"?
6"
6-8"?
1&3/8"? 1&1/8?
? BCCH is larger than CACH
4 -10'
4-8'?
6-15'?
4-15'?
Brown-headed Nuthatch
prefer large?
4.5-8"
1.25"
5-20'
3-13'
Bufflehead
7 x 7"?
10 x 10"
6 x 8"?
18-20"
10-15"?
16"?
16-18"
14"?
9-13"?
2.5-3"
2&7/8"?
5-15'
10-20'
Carolina Chickadee
4x4
8"
6"
1&1/8-1.5"
? CACH is smaller than BCCH
5-6' P
10'?
Carolina Wren
4 x 4"
6 to 8"
4 to 6"
1.5"
1&1/8"?
5 -15'
6 to 10'?
Chestnut Backed Chickadee
1&1/8"
5-15'
Common (and Barrow's?) Goldeneye
10 x 12"
25"
20-23"
3" high x 4" wide
4x5 oval?
20-30'
10 minimum?
Downy Woodpecker (roosting)
4 x 4"
9-12"
6-8"
1.25-1.5"
1.2-1.4"?
6-20'
8-50'?
Flicker, Northern
7 x 7" or
6 x 8"
16-18"
13"
(14 to 16")
2.5 -3"
6-20'
12-20 best
Great Crested Flycatcher
6 x 6"
8-10"
6-8"
1.5-2.5"
2"? 1&3/4? pref over 1 9/16"?
8-20'
4-10'?
Hairy Woodpecker
6 x 6"
12-15"
9-12"
1.5-2.75"
1.5"?
1.6-1.8"
12-20'
8-20'?
15-45, esp. 35'?
Hooded (and common?) Merganser
9 x 10"
10 x 12"?
25"
18"
20-23"?
3.5 x 4"
4x5" oval
3-20'
10' minimum
House Finch          
House Wren
4 x 4"
6-8"
4-6" or 7"?
6"?
1-1.5"
(1&1/8"?)
1.25"?
6-10'
will nest at 5'
5-10'?
Kestrel, American

8 x 8"
8 x 9.5"?
10 x 10"

 

16 to 18"
12-15"?
13 to 15
9-12"?"
3"
3.25"?
10-30'
15-20'?
20-30'?
10-35'?
Lewis's Woodpecker
7-7"
16-18"
14-16"
2.5"
12-20'
Mountain Chickadee
1.25"?
4-10'
(6-15' P)
Prothonotary Warbler
4 x 5.5"
8-10"
6-8"
1&1/8 to 1.25"
6-15'
Purple Martin
6 x 6"
6"
2"
2 to 2.5". Use Starling Resistant Entrance Holes
10-20'
(15-20')
Pygmy Nuthatch
4x4"
8-10"
6-18"
1.25"
5-15'
8-60?
Pygmy Owl
6x8"
10-15"
9-13"
2.5"
10-20'
Red-bellied Woodpecker
6 x 6"
14"
12-15"?
11"
10"?
2"
20'
10-20'?
33-72'?
Red-breasted Nuthatch
4 x 4"
8-10"
6-8"
6-18"?
1&1/8-1.5 "
1.25"?
12-20'
5-15'?
6-40'?
Red-cockaded Woodpecker (Picoides borealis)
Smear box with white paint and caulk to simulate dried sap.
slope hole upward about
5 degrees from outside to inside. Create sap wells above, beside and below with chainsaw.
15-18' on tall longleaf, loblolly, and pond pine with low understory
Red-headed Woodpecker
6 x 6"
12-15"
9-12"
1.75-2.75"
2"?
face S/W
12-20'
10-20'?
24-65?
Saw-whet Owl
6 x 6"? 7x7"?
6x8"?
10-12"
15"?
10-15"?
8-10"
9-13"?
2.5-4"
2.75"?
12-20'
Screech Owl
8 x 8"
12-15" 16"?
9-12"
13"?
2.5 to 4"
3"?
10-30'
12-40'?
10-30'?
Tufted Titmouse
4 x 4"
8-10"
6-8"
1&3/8-1.5"
6-15'
Tree Swallow
6 x 6"
5 x 5"?

5"
6"?
6-8"?

5"
4-6"?
1.25?-1.5"
Will nest in boxes 5-5' high
10-12'?
6-16'?
5-15'?
Violet-green Swallow
5 x 5"
6"
6-8"?
1 to 5"
4-6"?
1.25-1.5" round (prefer 1&3/8"?)
7/8 x 1.5" slot

10-12'
High preferred
5-15'?
4-5?
16-80 avg 43'?

White-breasted Nuthatch
4 x 4"
9-11"
6-8"?
8-10"?
7-9"
6-8"?
6-18" ?
1&1/8-1.5"
1.25"?
1&3/8"?
12-20'
5-15'?
at least 8'?
Wood Duck
10 x 18"
10 x 10"?
9 x 10"?
10-24"
25"?
12-16"
18"?
3"-4"
3.5 x 4"?
4"? Elliptical preferred?
10-20'
3-20'?

*Mountain Bluebird and Western Bluebird ranges overlap in some areas, and Mountain's need a 1 9/16" hole. Some Western's are larger than others. So the 1 9/16" hole is a safe bet, and will also exclude almost all starlings.

References and More Information:


Bluebirders need to think "inside the box."
-Doug Zimmerman


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