How to monitor a Bluebird box or trail


Many people put up nest boxes with the best intentions of doing the right thing, but for various reasons, after a time the houses go unchecked and forgotten. It is tempting to think, “I put up a box; the birds can take care of themselves; I’ll leave it up to nature.”  Other folks with good intentions will put up a box in a habitat that is inappropriate for the species they are trying to attract, and/or is susceptible to hostile takeover by house sparrows (non-native predators) and simply give up, allowing the house sparrow to win. This
box now becomes a “house sparrow haven”.

Unfortunately, allowing these scenarios to play out does far more harm to ALL native cavity-nesting birds, not just the bluebirds.  It is best to take down the “unmonitored box” or plug up the entrance holes. We encourage you to learn more about house sparrows and other predators before you put up ANY box.  Putting up a nest box is a commitment to monitoring it. Monitoring it, as you will experience, can be great fun for the entire family, is educational, sometimes surprising and incredibly rewarding.  So let’s get started.

Your 1st check should be done in late winter or very early spring before nesting starts. Check for gaps or holes in roof or sides; use silicone caulk. Repair or replace a cracked roof. Is the box securely fastened to the pole? Wood can shrink or expand so things may need to be tightened. Does the box open easily? Front or side may need to be sanded or loosen some screws. Has the entrance hole been enlarged? (woodpeckers, squirrels and raccoons will chew entrance holes). This is easy to correct by installing a 1.5″ hole guard made of metal, hardwood or slate.  Hole guards re-establish the original entrance size and can be attached with screws.

A bluebird nest is a cup-shaped nest of fine woven grasses or white pine needles. Bluebird eggs are light blue and early nests may have 4 or 5 eggs. Black-capped chickadee nests are made of moss base and covered with animal fur cup with small orange eggs with dark
red spots; perhaps 6 to 8 eggs.

Wrens have nests full of small sticks with a small grass cup near the back of nest for eggs.  Tree swallow nests resemble bluebird grass nests but always have a blanket of white feathers; 5 or 6 white eggs complete their nests.

Bluebirds will NOT nest in a box occupied by wasps. To prevent paper wasps from attaching their home on the ceiling, rub bar soap or paint liquid soap on the ceiling. Wasps will be unable to attach their home.

Ants, gnats and earwigs swarming over unfeathered nestlings can cause bites and death. Diatamaceous earth dusted under the nest will discourage the pests.  Also, put some at the base of the pole.

For ants, a 2″ band of Tanglefoot on the post under the box will stop them.  Pyrethrin-based products are the only products recommended for use in boxes but BE CAREFUL with chemical sprays.  It may hit eggs or nestlings and be a big problem! A light dusting of diatomaceous earth or cinnamon under the nest will drive the ants away.

A wet nest can be deadly to nestlings and is more likely to happen in early spring when temperatures are cooler (1st nesting season).
Top-opening boxes, leaky roofs and clogged drainage holes can all lead to moisture and water accumulation in nesting boxes. Also, ventilation holes on the western sides of boxes may allow water seepage.  If the nest becomes wet, this leads to hypothermia of the nestlings. Mother is unable to brood the chicks and keep them warm. When checking a box, it is important the check the nest itself and not just the nestlings. If the weather is cool and a wet nest is found, a wet nest can be replaced. The nestlings can be removed with care, placed in cloth in a box, and a new cup-shaped nest made out of dry grass can be made to replace the old one. (try to save old nests from year before in a zip lock bag for this purpose, ie, abandoned nests or unused nests).  Western side ventilation holes made be covered with a plexiglass disc during this early time and as the season warms up, the disc may be gradually turned to 1/2 or full open.  This technique was used on my Lancaster Country Club trail to solve “wet nests” problem.

Boxes that are placed too close to barns, farmsteds and feedlots where animals & poultry are fed are very susceptible to house sparrows. Boxes placed in such areas will not be successful for bluebirds  unless strict monitoring is done. Also, bluebirds that nest in areas with a high sparrow population are vulnerable to sparrow attacks, commonly killing the adult bluebird in the box and destroying the eggs and or nestlings.  Boxes placed in these areas should be moved to a more suitable
location or a sparrow trapping program started.
Control of sparrows on a bluebird trail can be either PASSIVE or AGRESSIVE. Passive means to control sparrows by taking preventative measures when placing the boxes to deter sparrow use. Also, using box models that sparrows dislike, ie, slot-boxes, PVC, etc.  Aggressive measures means trapping the sparrows after the box is placed. In-box traps can be used for single sparrows or large box traps for large groups.

The house wren is quickly taking over the sparrow’s long-held title as “the bluebird’s worst enemy”. Wrens can pierce or carry out bluebird eggs and will sometimes kill nestlings.  Not that long ago, a box placed 50 feet from cover (bush or trees) was considered safe from wrens. Now, because of over population of wrens on bluebird trails, 200 feet is considered the “safe” distance.  To avoid this growing problem, place your boxes away from wren habitat whenever possible. Avoid brushy and heavily wooded areas. Bluebirds’ 1st nesting attempts are usually safe from wrens as the wrens arrive later in the spring (late April).

Ideally, a box should be mounted in a manner that denies wildlife access to it. Once a raccoon discovers he can get into a box or series of boxes on a trail, he will raid them on a regular basis and your trail will become a “predator highway”.  Mounting poles can be greased or coated with silicone spray.  This will greatly deter raccoons and snakes.   A “Ron Kingston baffle” can be placed on the pole and it will stop all predators including snakes.  A “Noel predator guard” is very effective for keeping both raccoons and cats out of boxes.  Using both types of predator guard, ie, “double predator guarding” increases your odds of providing a SAFE nest box for bluebirds.  I use “double predator guard” method on ALL my boxes.

It is very important to remove the nest as soon as the nestlings have fledged, making the box available for other nesting attempts.  With a putty knife and paint brush, thoroughly clean out the box. Spray with a 1 part bleach (chlorox) to 10 parts water solution and allow to dry.  Mother bluebird likes to start out with a fresh nest of cup-shaped grass or pine needles for each  brood; soiled and matted down nests need to be removed.


Here are some items that should be in your monitoring kit:

report forms
2″ mechanics mirror
box closures
hole reducer (various sizes)
plastic bags
plastic spoon
duct tape
house sparrow trap
mask & gloves
diatomaceous earth
extra nest
putty knife/spatula
spray bottle/ 1:10 solution of bleach & water
garbage bag
portable stool/small step ladder
zip ties
garden shears
paint brush
wire cutter
utility knife
needle-nose pliers
hose clamp
tube of liquid nails
Grip ‘n Grab  (for picking up trash and cans)
wasp/hornet spray

Weekly Monitor Form (Download PDF)

Under most circumstances, monitoring your nest box 1 time per week is sufficient. You don’t have to worry about scaring off adult bluebird parents or tree swallows. They are quite tolerant of human monitoring and observation.  Start checking your bluebird box in mid-March for early nestings. Depending on the mildness of winter, it may be earlier. Bluebirds usually start to nest in late March or early April.  Make some noise or whistle when you approach the nest box. This will let any occupant inside know of your presence. Stand to the side, away from the entrance hole,  lightly tap on the box and slowly open the nest box door.

Avoid checking active nests during cold or rainy spells. A nest is considered “active” once the 1st egg is laid. Check nests for wetness after bouts of inclement weather.  Avoid checking nest boses during the morning hours. Bluebirds (and others) frequently lay their eggs during this time. You don’t want to startle a female that is “in process” of laying an egg.  Bluebirds lay one egg a day until the clutch is complete. Clutch size varies from 3 to 6 eggs and depends on weather, food supply, time of year and other variables.

Only the female can incubate the eggs and brood her chicks. She has a “brood patch” on her belly that allows her to transmit heat from her skin to the eggs or chicks. Incubation lasts from 12 -18 days. Brooding lasts, on average, 5-7 days but much depends on the weather. Brooding by the female is needed by the nestlings at this time to help regulate and maintain their proper temperature.

If you find a dead chick, remove it immediately. Dispose of it far away from the nest box.  Once the chicks have fledged, remove the old nest and clean the box with a putty knife and brush.  Soap and water or 1:10 bleach & water solution can be sprayed.  Bluebirds like clean boxes!

The main reasons for monitoring a nest box is: 1) to increase populations of native cavity nesting birds and 2) prohibit non-native House Sparrows and European Starlings from utilizing nest boxes. Never allow either of these birds to inhabit your boxes.  Always remove nests, eggs or young of non-native species!

The warm and rewarding feeling of regularly checking the bluebirds through their nesting cycle should be reason enough for monitoring your trail. Bluebirds are one of the few birds that readily accept human help and continuous observation. They enjoy human interaction and can even be trained to come to your yard for mealworms at the ringing of a bell or whistle.  Walking your trail should not be considered work, but a privilege.  It is rewarding to know that you are really making a difference.

Finally— it is time for the real excitement!  Spring comes; nests are built, eggs are laid, and the life they contain bursts out! You get to witness it all !