Dealing with Summer HEAT  
in Nest Boxes
(from Nature Society News July 2012 Column by Steve Garr)

            Much of the southern United States is reporting record heat and the heat is affecting our
bluebirds. With nesting season in full swing bluebirds are either incubating eggs or raising young. Our
Eastern bluebirds took advantage of the mild winter and starting nesting early. With two broods of
bluebirds fledged,  the third nest is now underway. The excessive heat they are experiencing now can
sterilize the eggs or kill the young inside the nest box. Sometimes you can locate the nest box where
there is afternoon shade, and that will help, but when temperatures reach above 100 degrees even that
may not be enough. Trees act like air conditioners cooling the surrounding area so the closer you position
the nest box to the tree the cooler it will be.

Even with a well designed bluebird box with extra roof overhang and good ventilation you still have to
worry when the temperatures exceed 100 degrees. The inside of the nest box is often 5 to 10 degrees
warmer than the outside temperature. There are a few things you might add or change on your nest box
to help keep the inside cooler. Consider adding a second and larger roof with a gap for air ventilation
between the two roofs. Since it is hotter in the afternoon with the sun baking the side of the nest box
also look at adding a second wall on the west side of the nest box as well.
            Another option is changing the color of the nest box. As your nest box gets weathered it does
not reflect the heat as well and tends to absorb the suns heat instead of reflecting it. Unpainted natural
nest boxes will get hotter as they age and during the summer absorb more heat. Even if it is only a few
degrees difference between a new box and an older weathered nest box that few degrees may be critical
to the eggs or nestlings inside the box. Test have shown that the best colors to reflect the sun’s rays
and heat are white and aluminum. You could paint the roof and the western facing side or renew the
entire nest box. Just the outside of the nest box is all that would need to be painted and a latex paint is
your safest option for the birds. Even a light coat of paint will seal some of the cracks and help reflect the
sun’s rays keeping the nest box cooler. An added benefit will be the life of the nest box. You will probably
have that nest box several more years before it needs to be replaced. Another solution is aluminum
flashing cut to cover the roof and the sides. Most hardware stores sell aluminum flashing and are often
available by the foot. You can easily cut the flashing to the size you need and tack it to the side and top
of the nest box. If you separate the aluminum flashing from the roof and sides with spacers will allow an
air gap for ventilation, the air gap will act as added protection from the heat.
           The last option- one that is not usually available on the bluebird trail but is possibly an option in
your yard- is a misting system. One misting nozzle positioned a few feet above the nest box spraying into
the air will lower the temperature. The finer the mist the more effective it will be for evaporation and
lowering the temperature without getting everything saturated. Misting nozzles similar to those used in
outdoor restaurants in the South West work extremely well, but any type of misting system will work.
Please, consider adding extra roof overhang to keep the inside of the nest box dry. Be aware that a lot of
the misting systems used in landscaping are designed for saturating an area and do not evaporate as well
as those used by restaurants. Some of the bird misters that are available spray a finer mist than the
landscaping misters.
           One danger of the heat and drought that we must also consider is predation. During droughts
raccoons and snakes are more determined and motivated to defeat baffles that have always worked. The
smell from nest boxes stained with droppings or old nest that were not removed intensifies with the heat.
A thorough cleaning will help eliminate the odor and help protect the new eggs and hatchlings. Effectively
cleaning the nest box with the proper products can also kill mites and parasites. Some of the new natural
enzyme sprays target these problems and are safe for you and the birds. Old remedies of a saturated
solution of bleach and water do not target all of the problems found inside the nest box.  Addressing the
issues of increased parasites inside the box can often be overlooked because sometimes it just is not as
obvious to us. Particularly during times of extreme heat, however, it is important to be just as concerned
about the invasion of parasites that can happen inside the box, as we are about the predators that attack
from the outside of the box.   

Taken from Steve Garr's July 2012 Column in the Nature Society News
Left: A Tree Swallow
nestling watches
from inside the box
as Steve Garr reads
the temperature
inside a nest box on
his trail in July.
has installed a reflective
shield of aluminum on the
"sun-side" of the nest box
to help deal with the
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Steve installs an extra roof (with
spacers) on box 201 on his city
nest box trail in Jefferson City, MO
The Bluebird Pair from Box 201 wait
patiently as Steve makes adaptations
to their box to help reduce heat inside
Left: it doesn't take long before
the Bluebirds are carrying insects
to the newly remodeled nest box
to feed their five nestlings inside.

Right: The male Bluebird finds the
Aluminum flashing heat reflectors
Steve installed a handy perch to
feed nestlings inside the box!