Recommended Nest Box Specifications – Bluebirds Across Nebraska

3/4 inch wooden boards or PVC pipe with attachable wooden roofs are commonly used for bluebird boxes. Peterson boxes often use 2 x 4 inch boards
Do not use pressure treated wood because they include toxic compounds
Paper milk carton style or corrugated cardboard boxes are unacceptable
Woods such as redwood and cedar are long-lasting even when left natural

Eastern Bluebirds use 1 ½ inch round holes, 1 3/8 x 2 1/4 inch vertical oval holes, or 1 1/8 inch horizontal slot entrances
Western and Mountain Bluebirds use 1 9/16 inch round openings
Where these species overlap use 1 9/16 inch round openings
Oval holes should only be used in eastern bluebird boxes with moderate to small dimensioned boxes to reduce the possibility of starling use

Eastern Bluebirds: floors in wooden boxes should be approximately 4 x 4 inches or 5 x 5 inches (Peterson style boxes are some what smaller), floors of circular boxes (such as PVC pipe) should be approximately 4 inches in diameter
Western or Mountain Bluebird boxes should be at least 5 x 5 inches or 5 ½ x 5 ½ inches to accommodate larger clutch sizes

It is imperative that all bluebird nest boxes open readily from the top, side, or front to facilitate box monitoring and cleaning
If box sides or front pivot to allow access to the box, they should do so at as high a point as possible to ensure that you can observe tall nests without the door obstructing your view
A screw or angled nail in a pre-drilled hole should be provided to ensure that mammalian predators can not readily open the nest box

Natural wood is acceptable
If painted or stained, use light colors to minimize having the box overheat during warm weather in areas where overheating is likely

Drainage holes must be provided ‘in the box bottom to allow any rain entering the box to drain from the box and to provide air circulation to keep nesting material dry
The box should be water-tight
The roof should provide sufficient overhang beyond box entrance or vent holes to minimize possibility of rain entering these openings
The roof should cover top edge of the box back unless other features eliminate any possibility of rain entering the joint between back and roof of box even if the wood warps

Vents providing cross ventilation should be present near the box peak. These openings should be protected from rain by having the box roof overhang a sufficient amount to minimize precipitation entering the box.
Dark colors should be avoided to minimize overheating
It should be possible to plug or cover vent holes during cold weather periods early in the nesting period
Long roof overhangs minimize the possibility of letting sun, rain, or snow entering the box

The box should be easy to mount on a predator-resistant post in areas with raccoons or cats
A 5 inch roof overhang above the entrance hole reduces the possibility of raccoon or cat predation
Wooden guards placed over the entry hole are not effective in eliminating raccoon predation
Very deep tunnel-like predator guards deter bluebird use
Boxes mounted on heavily greased pipes or on waxed metal electrical conduits will deter many climbing predators
Mounting boxes less than 5 feet from the ground increases the opportunities for climbing or jumping predators to raid the nest
Wooden posts, ungreased pipes, PVC pipes are readily climbed by nest predators such as raccoons

Boxes should be designed so that they may readily and securely be mounted to a support post such as water pipe or electrical conduit
Fence posts are acceptable mounts in areas where raccoons are rare
Having the back extend beyond the main box body below or above the box will allow you to attach the box with screws, nails, pipe clamps, wires, or u-bolts

Perches should never be used on any bluebird boxes because they are not needed by bluebirds and only facilitate harassment by non-native species such as House Sparrows

Interior walls should not be painted or stained
The front wall below the entrance hole should feature a rough surface to facilitate chicks climbing to the entry hole

Nest boxes with raised screen floors may reduce blowfly infestations but this has not been conclusively proven
Rotenone should never be applied to the interior of nest boxes as it is counter-productive in controlling blowflies

For further information/membership contact:

Bluebirds Across Nebraska
P. O. Box 67157
Lincoln, NE 68506-7157