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NABS Nestbox Specifications
NABS
operates a nestbox approval program which lends its seal to commercial
nestbox manufacturers as having incorporated the minimum specifications
listed below. For manufacturers or retailers interested in having
their nestbox reviewed, please click here.
Materials
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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
Entry
Holes
-
Eastern
Bluebirds use 1-1/2 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
the ranges of the 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
Floor
Sizes
-
Eastern
Bluebirds: floors in wooden boxes should be approximately 4 x 4 inches
or 5 x 5 inches (Peterson style boxes are somewhat 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 5-1/2 x
5-1/2 inches to accommodate larger clutch sizes
Access
-
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
Colors
-
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
Water-Resistance/Drainage
-
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
Heat/Cold
Protection
-
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 sun, rain, or snow entering
the box
Predator
deterrence
-
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
-
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, un-greased pipes, PVC pipes are readily climbed by nest
predators such as raccoons
Mounting
-
Boxes
should be designed so that they may readily and securely be mounted on
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
Inner
Walls
Parasite
Control
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