Monitoring Bluebird Nest Boxes

It is very important that bluebird nest boxes be actively monitored (checked) at least once a week. Doing so increases the chances of success for bluebirds using the box and also is valuable for determining population trends. A box that is not monitored may be more harmful than helpful to bluebirds. All bluebird boxes should be built so that they can be opened either from the side, front, or top.

Monitoring nest boxes will alert you to problems the birds may be having with blowfly parasitism. Uncontrolled, the larvae of this species may weaken or possibly even kill the nestling bluebirds. If you identify larvae in the nest, you should replace all the nest material with dried lawn clippings in a shape similar to that of the original nest. This will increase the chance that the chicks will survive. Many bluebird enthusiasts replace all nests holding chicks periodically even before the blowfly larvae are visible. You should also replace any nest with young birds that has been saturated following rainfall. This is especially important during cold periods.

Being aware of what species is using the box is also beneficial. Bluebird societies would like you to monitor and report all species using your nest boxes, not just bluebirds. Species such as bluebirds, tree swallows, house wrens, and chickadees are all native and beneficial birds. Mail survey forms submitted at the end of the nesting season allows the identification of population trends in each species.

House (English) sparrows and European starlings are non-native species introduced from Europe and their aggressive seizure of cavity nest sites is the main reason for the rarity of bluebirds today. Starlings nest in many of the natural nest sites but can be excluded from nest boxes by only using 1 1/2 or 1 9/16 inch entrance holes. House sparrows can readily enter bluebird nest boxes and frequently kill bluebirds, destroy their eggs, or drive them from their nests. At no time should they be allowed to successfully nest in bluebird boxes. Doing so will increase the house sparrow population and further reduce the number of the bluebirds.

After any nesting effort has ended, either due to nest failure or successful fledging of the young, the nest should be removed from the box. If a bluebird nest was successful, re-nesting in the same box will be encouraged if the first nest is removed. This should be done when all chicks have left the nest.


Whenever you monitor a box you should determine what species is using it by examining the nesting material and eggs. You should record the date, and the number of eggs or young that you have observed. Knowing when the eggs where laid will help you determine if they are infertile, or when they should hatch and when the young would be expected to leave the nest. In the case of bluebirds, the eggs are laid one each day until the entire clutch is complete. Incubation will then begin and will last approximately 13-14 days. After hatching the chicks will remain in the nest for 17-18 days. Your monitoring should be limited to viewing from a distance after the 13th day or the chicks might fly from the box prematurely.


Nest monitoring should only be done during calm, mild, and dry weather conditions to reduce the chance of chilling the chicks or eggs. Open the nest box being careful not to allow the eggs to fall out or chicks to jump out. Songbirds have a very poor sense of smell and will not abandon the nest due to your handling the nest, eggs, or chicks. If chicks are in the nest, look under the nest for signs of blowfly larvae. The chicks themselves should be examined for small scars, particularly under the wings which indicates blowfly parasitism. Sometimes you may observe the larvae attached to the chick. These are easily removed by hand. Complete the monitoring as quickly as possible to minimize disturbance. When handling the chicks or removing them from the nest they should be placed in something that will protect them from the sun or wind while preventing their escape. Avoid disposing used nest material near the nest site or predators may be attracted to the site. Always be certain to close the box door securely before leaving. Record what you observed.


Bluebird: The 1-4 in. tall nest is built with fine grasses or pine needles with a fairly deep nest cup. Eggs (4-6) are powder blue or occasionally white.

Tree swallow: Their nest is also made of grasses but they may use somewhat coarser fibers than a bluebird. The nest generally has a flatter cup than the bluebird's and is usually lined with feathers or occasionally scraps of paper. Eggs (5-7) are white and smaller than those of a bluebird.

House wren: Wrens fill a nest box with sticks and line the deep nest cup with fine plant fibers or feathers. "Dummy nests" without the nest cup are often built in all other cavities within the male wren's territory to reduce competition for resources. The eggs (6-8) are tan, speckled with brown and quite small.

Black-capped chickadee: Chickadees build a nest of moss and plant down with the nest cup lined with hair. They lay 5-8 white eggs covered with brown speckles. Eggs are often covered with moss when the female leaves the box.

House sparrow: House sparrows build a tall nest of coarse grasses, often with pieces of scrap paper, cellophane, or other garbage. The nest forms a canopy with a tunnel-like entrance to the 5-7 cream-colored eggs with brown markings.


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