Bluebirds are one of the most admired birds in
North America. The popularity of bluebirds has
landed them in stories, poems and movies where
they symbolize love, happiness and renewed hope.
Individuals have increasingly become aware of the
joys of viewing bluebirds and providing them
artificial nesting sites.
Some of the earliest records of bluebird
conservation came from the journals of Henry
David Thoreau, naturalist and writer born in
1817. Thoreau's writings mention eastern
bluebirds returning to their boxes, giving
evidence that people were already providing nest
boxes in the early 1800's, possibly even in the
Eastern bluebirds seem to have been common at
this point in time and somewhat stable until the
introduction of two bird species from Europe the
house sparrow in 1850 and the starling in 1890.
Starlings and house sparrows use bluebird habitat
and compete fiercely, forcing birds out of usable
spaces or even killing them. Both the exotic
house sparrow and starling spread uncontrollably
and were widespread by the early 1900's. At this
time, the population of bluebirds began to fall
in response to both the presence of too many
house sparrows and starlings and the loss of
Individuals recognized the shrinking populations
of bluebirds and began creating bluebird
"trails"--series of nesting boxes
placed along roads, around the 1930's.
The continuation of this effort on a larger scale
from the early 1970's to the present time has
undoubtedly had a significant effect upon the
return of bluebird populations.
Bluebirds belong to the thrush family, Turidae,
whose members are known for their singing
ability. The Turidae family is comprised of 19
species including the popular American robin.
There are three distinct species of bluebirds;
the eastern, western and the mountain bluebird.
The coloration of the eastern bluebird differs
somewhat between adult male and female birds. The
male is dark blue on the head, back, wings and
tail. It is reddish brown from the chin down over
the breast. The belly is white. Females are a
lighter blueish-gray on the back, wings, head and
tail. They also have a lighter reddish color on
the breast and are white on the belly. Some
females appear almost all brown while others are
more similar to the adult male.
The adult male mountain bluebird is sky blue on
top of the head, back, wings, and tail. It is
lighter blue from the chin to the belly and
gray-white on the lower belly and under the tail.
The female is greyish on the head, back, throat,
breast and flanks. The wings and tail are sky
blue. Mountain bluebirds are slightly larger than
Eastern bluebirds. They measure about five inches
in length and have longer wings, which extend
about three-fourths the length of the tail when
Male Western Bluebirds have deep blue upperparts
and throat, with some rusty coloration on the
upper back. The breast and flanks are chestnut,
and the belly and undertail coverts are grayish
white. Females look similar, but less colorful:
brownish gray above, with breast and flanks
tinged with chestnut. The throat is pale gray,
and a prominent white eye ring is evident.
Bluebirds feed primarily on insects, crickets,
spiders and beetles in the spring and summer.
Perches such as fence posts, fence wires or
highlines are often utilized to view for
unsuspecting insects. If perches are sparce,
bluebirds will hover overhead much like a hawk in
search of prey. Bluebirds will utilize wild
fruits, berries and seeds during the fall to
prepare them for their migration south.
Once a female arrives on the territory, the male
will begin a variety of behaviors which will
attract a female and tend to call attention to
the various nest holes on the territory. For
example, the male may repeatedly poke his head in
and out of a nest hole or cling to the side of
the box and do a wing-wave display, flicking one
or bothg wings open at a moderate speed.
Once both birds go into the nest box several
times, they are generally considered paired and
will likely use that particular nesting site.
An accepting female will begin nest building
shortly after they have paired. At this point,
the male begins what is termed mate-feeding where
he collects food and feeds it to the female. They
keep in touch by calls and visual displays as
they fly about the territory.
The male follows the female closely as she
forages and builds the nest. The male is close by
both signaling her when it is safe to fly out of
the nest box and to prevent other males from
mating with her. Copulation can take place
anytime from the beginning of nest building until
the start of incubation. It generally takes place
close to the nest box and may occur on top of the
Bluebirds are cavity nesting birds meaning they
naturally nest in a hollowed-out area in a dead
or dying tree. This is different from other
songbirds such as robins and finches that build a
cup-shaped nest in the branches of trees or birds
like the meadowlark or horned lark that construct
nests on the ground.
They are further considered secondary cavity
nesters because they cannot excavate their own
cavities in tree trunks such as woodpeckers which
have heavy bills adapted for heavy pounding.
Today, one of the most utilized nesting locations
for bluebirds is the man-made boxes that mimic
the natural cavities provided by dead and dying
trees. This habitat has been limited throughout
the years by removal of old trees thought to be
of no benefit to wildlife.
In addition to natural and man-made cavities,
bluebirds have also been observed using crevices
in rocks and cliffs, drain pipes, mail boxes and
old farm machinery.
Nest Building and Incubation
As discussed earlier, the male bluebird takes the
lead in exploring habitat and attracting a mate
but the female is the one who makes final
determination of where the nest is built. This
process can be swift or it may take weeks. The
time utilized in this effort is usually dependent
upon the birds experience and whether they had
previously nested in that same location.
Females are in charge of all the actual nest
building. At times, the male may carry some nest
material but this seems to be a behavior to
stimulate the female to nest build and does not
amount to much in overall creation of the nest.
A nest normally takes around six days to complete
but may be interrupted and begin at a later date.
All of this is dependent upon weather and
individual bluebird habits. Pairs normally spend
less time building nests for their second or
During egg laying, the female leaves the eggs
unattended and begins incubating after the last
or second to the last egg is laid. She is also in
charge of incubating the eggs by herself. One
reason for this is that she develops a brood
patch consisting of an area on her breast where
feathers are lost and blood vessels increase.
This allows her to keep the eggs at the right
temperature for development, a task the male
could not perform.
During incubation, the female attends to the eggs
almost constantly. Eggs are incubated throughout
the night and during the day except when she
leaves the nest to preen herself or feed. On hot
days, eggs may be left for longer periods of time
since they maintain adequate temperatures without
While the female incubating, the male may come by
and sing or bring food. It may be a signal that
no predators are nearby and that she can safely
leave the nest. While she is away, the male will
remain close by and may even enter the nest box.
At night, the male may sit next to the incubating
Incubation for both species is about two weeks
but can be affected by weather. In cold springs,
incubation can actually take somewhat longer if
eggs experience periods of cooling.
Selection of proper habitat to place several
boxes or establish a bluebird "trail"
is vitally important. Most people make the
initial mistake of placing boxes in inappropriate
locations. These decisions either create
disappointment or may actually benefit
recruitment of unwanted and undesirable birds
such as the house sparrow.
Bluebirds are insect eaters and less competitive
for nesting space than are other cavity nesters.
Therefore, placement of nest boxes should be in
locations away from heavily wooded habitat
preferred by tree swallows and house wrens and
near open fields where insect hunting,
maneuverability, and visibility to avoid
predators is adequate.
Generally, open rural country with scattered
clumps of trees or low shrubs is best. Placing
boxes too close to shelterbelts and wooded areas
will attract house wrens and tree swallows, which
are also beneficial bird species. Examples of
good habitat include pastures, fields, edges of
country roads, cemeteries and golf courses. The
closer you get to buildings or urban areas, the
more chance you will have problems with house
sparrows which will actually kill bluebirds and
their young. It is also a good idea to avoid
areas where insecticide use is high.
Type of Nest Box
The type of box to purchase or construct to
attract bluebirds is a subject of much discussion
and there are probably as many ideas as there are
folks who maintain bluebird trails. Ideas come
from personal experiences and you will certainly
have your own opinion after a few years of
monitoring a few houses. There are, however, a
few basic ideas that have proven successful for
producing bluebirds and these guidelines provide
a good place to start. North
American Bluebird Society approved bluebird
Wood is probably the safest and best material for
nest boxes. Wood mimics the natural cavity, is
readily available, easy to work with and provides
good insulation qualities. The best woods to use
are cedar or redwood which withstand the elements
without being treated.
Choosing between different designs of wooden
boxes available shouldn't preoccupy a majority of
your time since most offer the same result for
the birds. Simply insure floor dimensions are at
least four by four inches for eastern bluebirds
and five by five inches for mountain bluebirds.
Avoid thin wood which will not maintain tolerable
temperatures inside the box. Also, do not use
varnishes or stain inside the nesting box. These
may be poisonous to the birds.
Both ventilation and drainage holes should
accompany any box. One-half inch vent holes in
the side of the nesting cavity will insure proper
temperatures are maintained inside the nest box.
The same sized holes can be drilled into the
corners of the floor to allow moisture to escape.
Entrance holes for eastern bluebirds should be
one and one-half inches in diameter and about
one-quarter inch larger for the mountain species.
Holes in an oval shape have also been developed
now under the presumption that birds can access
with less difficulty.
The box should not contain a perch and the roof
should overhang the entrance hole to keep rain
and sun away. The entrance hole should be about
six inches from the floor of the nest box.
Finally, one of the most important aspects is
that you allow easy access for monitoring. By
hinging either the top, front, or one of the
sides, birds can be checked at any time and nest
boxes cleaned easily.
Placement of Nest Boxes
Before you begin putting out any nest boxes, take
into consideration the location of preferred
habitat which was discussed above. Some locations
may not be suitable for bluebirds at all but will
be excellent for other beneficial species such as
the tree swallow.
Remember, a bluebird trail does not have to
contain a hundred boxes, it can be comprised of
as few as two boxes. The first step is to draw a
sketch of your property as you walk it,
visualizing potential locations.
Boxes should be located in pairs about 100 yards
apart. Ten to twenty feet should be left between
boxes in a pair. Pairing the boxes will allow a
more aggressive species such as the tree swallow
or house wren to nest in one of the boxes first
while allowing the second box of the pair for a
bluebird. This strategy is all based on bird
behavior because many bird species will not allow
another member of the same species to nest in
close proximity to their own nest but will allow
another species like the bluebird to nest.
Nest boxes should be attached to steel posts if
possible. Seven foot smooth steel fence posts
work extremely well and allow easy attachment.
Wooden posts allow predators to climb and access
nest boxes more easily. If you do use wooden
posts, predator guards can be attached.
Don't attach nest boxes to dead or dying trees
within a forested area unless you are attempting
to attract house wrens, chickadees, or
The recommended height for bluebird houses is
four to six feet from the ground. Bluebirds may
nest in higher locations but monitoring, viewing
and maintenance will be much more difficult.
Face the front of the nest boxes away from the
prevailing wind and in an easterly direction to
avoid the hot afternoon sun from shining into the
access hole. More important than this, face the
box in a direction in which the young fledgling
birds can reach a perch within about 100 feet. If
you are attaching boxes to existing fence posts
within a cattle pasture, put the boxes on the
side of the fence opposite that of the cattle so
they cannot be broken off by the cattle.
If you don't have adequate habitat on your own
property, consider approaching a landowner with
your idea. Also, be sure to obtain permission
before you attach any nest boxes to utility poles
or other private structures.
Monitoring and Maintaining Bluebird
Simply putting out bluebird boxes without
checking progress throughout the nesting season
can be doing more harm than good for bluebird
populations. One of the most important reasons
for monitoring is to prevent house sparrows from
using the nest boxes. Monitoring also allows you
to keep track of nesting results which are
important for contribution to the local wildlife
Begin checking bluebird boxes in mid-March and
continue checking each box weekly. If you cannot
find the time weekly, insure you check them at
least once a month. The note card shown below is
a good guideline and can be duplicated to provide
one for each nest box.
Record your results of monitoring as you move
around the trail, keeping the cards for reporting
overall information at the end of the nesting
season. Approach nest boxes and gently tap on the
outside of the box. Many times the bird will fly
off as you approach or when the box is disturbed.
This is normal and the bird will return after you
have checked the nest.
Females may also sit quietly on the nest as the
door is opened. In this case, close the door and
return later. Bluebirds are very tolerable of
humans. All birds have a poorly developed sense
of smell and touching around the box, eggs or
birds will not cause the bird to abandon the
nest. All of this is part of the enjoyment and
learning associated with a bluebird trail.
There is one time that nest boxes should not be
opened. This is the time period about ten to
twelve days after the eggs have hatched. Young
birds will have partially developed flight
feathers at this time and opening the box may
cause them to prematurely flutter to the ground
and become food for predators.
If you are not quite sure of the exact age of the
birds, it is best to play it safe and observe
from a distance or open the door only a crack to
peer in. Some folks have even gone as far as
using a small dental instrument mirror to view
inside the next box without ever opening the
On the fifteenth day after egg hatching, the
birds should have fledged and the nest should be
removed. Take the old nest out, as well as any
dead birds, and move the material away from the
area as this can attract predators.
Remove all house sparrow nests immediately. Be
sure that any of these nests are, in fact, house
House sparrows and starlings are not protected by
law and should be disposed of. All other
songbirds are protected and it is illegal to
tamper with or harm their nests in any way.
After the nesting season is over, clean out the
boxes and then recheck again in the following
spring. Some people simply leave the doors open
on the boxes to prevent small mammals from using
them as nesting areas.
Controlling Competitors and Predators
The goal of establishing a bluebird trail is to
attract as many bluebirds as possible. There are
obstacles that you will encounter with this goal
in mind and an understanding of the threat should
assist you in maximizing your bluebird return.
Some people consider tree swallows and house
wrens as nuisance birds. In actuality, these
birds are beneficial for insect control and they
are protected by law. As discussed earlier, avoid
placing boxes in habitat areas favored by these
species. Generally, the closer to wooded habitat,
the more likely you will attract these two birds.
House sparrows are the largest competitor of
bluebirds and concern over their competition is
justified. House sparrows are aggressive and out
compete bluebirds for nesting space. They will
actually destroy and dump eggs from a bluebird
nest and kill both young and adult birds when
encountered. The best method of preventing this
from happening is to avoid placing boxes in areas
close to known sparrow habitat-usually urban
areas, farmyards and any other location close to
Next, monitor nest boxes closely and remove
sparrow nests immediately upon initiation. If you
observe house sparrows beginning to build a nest
in a particular nest box, there are devices which
can be attached to the entrance of the nest box
which trap the live bird inside. Once caught,
they can be destroyed. There are also large live
traps available on the commercial market which
will trap numerous birds at once and can be
successful in removing local house sparrow
In addition to damages that may be caused by
other songbirds, a number of other wildlife
species, domestic cats, and insects can be
potentially harmful to bluebird production.
Even though predation is part of nature, steps
can be taken to lessen the amount, especially in
the case of domestic cats which are not part of
nature and can be controlled. Raccoons, snakes
and cats all must enter the nest box by climbing
unless they can reach nest boxes by jumping from
tree limbs or other objects that are located too
close. By wrapping an apron guard made of sheet
metal around the post about a foot under the nest
box or by placing a four inch piece of PVC around
the post, these species will not be able to
access the nest box at all.
Hawks such as the cooper's and sharp-shinned and
falcons like the kestrel eat songbirds including
bluebirds. Again, this is entirely natural and
should not alarm you. Hawks and falcons are only
doing what they do to survive and this must be
accepted. Bluebird losses can be limited by
avoiding the placement of nest boxes underneath
perches such as high line wires or in known
raptor nesting areas.
Blowflies are a type of fly that lay their eggs
in bird nests. The larvae that hatch from these
eggs will feed by sucking blood from the young
birds. Larvae will feed during the night and
crawl back into nesting material during the day.
To check for larvae, lift up the bottom of the
nest and tap it gently. If you find any larvae,
brush them out. If larvae are in extremely high
numbers, discard all the old nesting materials,
brush out the box, and fashion a new nest with
fine grasses. Replace the nest and return the
Paper wasps and yellow jackets may also decide to
take up residency in a nest box. Check on the
bottom side of the roof when the temperature is
cool in the evenings.
Insect nests can be scraped out with a putty
knife or knocked out with a stick. Do not use
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