Quick Tips: Clean out nestboxes as soon as the baby birds fledge, or at a minimum at the end of the nesting season. Avoid inhaling dust/detritus! Dispose of the nest far away.
Why clean out a nestbox: Unlike House Wrens, Bluebirds will not typically clean out old nests by themselves. They may build a nest on top of another previously used nest, but this may promote disease and parasite infestation, and increase the likelihood that a predator will be able to reach in and nab eggs/nestlings that are closer to the entrance hole. The detritus can also attract fire ants, and accumulated feather dander can make the interior dusty, especially when older fledglings are exercising their wings. Also, most birds won't use a box filled to the top with House Wren sticks. (The presence of a used House Wren nest may actually encourage House Wrens to renest, which not all trail monitors consider desirable.) Cleaning out a nestbox after each use enables monitors to know whether a box is used again, and by what species.
When to clean:
First of all, be sure it is not an active or new nest. Some birds can build a nest very quickly.
Never remove active nests of native birds! That is illegal. If, for example, you have a chickadee using a box and you want bluebirds, put up another nestbox.
By removing nests right after fledging, or at least at the end of the breeding season for your area, you will avoid the common mistake of removing a new nest.
In my opinion, you should remove used nests as soon as the young fledge (birds in the North begin another clutch an average of 17 days later, in the South 26 days), or if nesting fails (since they may try again in 1-7 days), to encourage another brood.
At a minimum, clean out the box when nesting season is over.
During active nesting season, I do NOT remove a clean nest even if it appears to be abandoned, as the bird may just be taking a break from building.
Unused Nests: Sometimes egg laying does not begin until weather or food supply improves. Removing an apparently unused nest prematurely may cause the birds to move elsewhere or lose precious time rebuilding. I have had completed nests vacant for weeks, and then suddenly eggs are laid. If the birds started a nest and then left it for some reason, or completed a nest and then left or were killed, the nest material can be left in the box as it may be used by other birds or maybe even the same birds who deposited it in the first place. Many monitors save completed, unused bluebird nests in case a nest change is needed. Note that Black-capped chickadees will not return to a failed (predated) nest site.
Failed Nesting: I do NOT remove a bluebird nest after a failed nesting. If they want to try again in that box, having an existing nest will save them time. Do remove any dead nestlings immediately. Do try to address the cause of failure if possible to prevent a recurrence. Some species like chickadees are unlikely to renest in a box where the first nesting failed.
You can leave unhatched eggs in the nest (sometimes the parents will remove them.) However, if a spoiled (a "bad" egg that started to develop and then died) egg breaks, it can make a mess and attract insects. Also, an unhatched eggs could possibly cause a developing hatched chick to develop splay legs. HOWEVER....
Be aware that for most species, incubation does not begin until a full clutch is laid (so all young will hatch close together). The nest may not be regularly attended until that time, so do not assume it is abandoned!
Sometimes incubation is interrupted or delayed (e.g., to cold temps) so eggs can take longer than expected to hatch.
Depending on the species and temperatures, some eggs in a clutch may hatch later than others, and normal hatching can take 24-48 hours. Do not remove unhatched eggs until at least 72 hours have elapsed since the last chick hatched.
If eggs were laid and then clearly abandoned, you can clean out the box after you are 100% convinced that the nest was abandoned. Certainty can be achieved by ascertaining that there is absolutely no adult activity for a prolonged period, a period at least as long as the normal incubation period for whatever species laid the eggs plus a few weeks (since the start of incubation may be delayed due to weather.) Many times people think a nest is abandoned when it is not! The incubating female is either secretive (as in chickadees and titmouse) or is not on the nest as often as you would expect (e.g., because outside temperatures are warm.) You must be SURE! When in doubt, wait it out.
If eggs were laid and none hatch, they should be left in the box as long as there is adult activity. If they are infertile, the parents may remove them, build a nest nest on top of them, or lay more eggs with the unhatched eggs. You won't be able to tell which are the old eggs and which are new ones! When you are 100% convinced that there is no longer any adult activity, clean out the eggs. I usually leave the nest in place to save the parents time if they decide to lay another clutch.
Newly born hatchlings are VERY fragile. Avoid moving them to get to an unhatched egg until they have feathers, or use a plastic spoon to remove the egg.
Leave the nest if it is clean - it will save the birds precious time and energy to be able to re-use it if they lay a new clutch.
A "hive tool" is useful for cleaning out nestboxes or dealing with paper wasp nests. You can also use an inexpensive putty knife.
How to clean out a nestbox:
Have everything ready so you can work quickly (but carefully.)
Stand upwind to avoid inhaling dust and detritus. Some people put on a painter's dust mask first.
Remove any empty nest and put it into a plastic bag (you can invert the bag onto your hand like a glove to avoid touching the nest). Close the bag (e.g., with a twist tie) in case there are any insects/mites or larvae in the nest.
If there are eggs in the nest, try not to touch them with your bare hands. The oil on skin can interfere with hatching, by clogging up air pores in the egg shell. Use gloves or a plastic spoon, but be careful - if you drop an egg it WILL break.
If there are nestlings in the nest, take out the whole old nest with the nestlings still in it, and put it in a little shoe box or bucket with a towel over it while you're working. This will help keep them warm and calm. When you transfer them to the new nest, be very gentle and do not roll them around in your hand - newborns are fragile.
Brush out (with a stiff brush like those used to clean a grill) and scrape the interior (a hive tool [available from bee supply stores], putty knife or paint scraper is
useful). If you find any paper wasp nests, remove them, as they may attract more wasps (and boxes with paper wasps usually go unused by birds). If drain holes are plugged with debris, clean them out too.
If desired, disinfect boxes with a 10% bleach solution in a spray bottle. If you do use bleach, leave the box open for a day to air and dry it out. You can rinse it out with some water if you have some handy, but chlorine oxidizes rapidly and becomes harmless, and should be gone in 24 hours (e.g., within 24 hours, chlorinated tap water is suitable for fish to live in).
Dispose of the nest far away or in the trash to avoid attracting predators. Since the beneficial Jewel Wasp parasitizes blow fly larvae, some people like to dispose of the nest outdoors, or put it outdoors in a bucket with a screen top that allows the wasps to escape but leaves any blow flies behind.
Special precautions for cleaning out a box that housed mice to prevent infection with very rare but potentially deadly Hanta Virus: Before removing a used mouse nest, use a spray bottle to thoroughly soak the nest and box (to control dust) with a 10% bleach solution (water if no bleach is available). After 15-20 minutes, while standing upwind/wearing a dust mask, use gloves or a plastic bag to remove the nest, and then sweep and scrape out the box. Wash your hands afterwards. Leave the box open for a day to air it out.
Note: I haven't seen any conclusive studies on whether bluebirds prefer a box with old nesting material in it (perhaps as a sign that this cavity had been used successfully in the past.) Because of the risk of predation and parasites, I choose to remove old nests. One study concluded that there was no relationship between a bird's choice of a clean or dirty nestbox and incidence of blow fly infestation (Kast, Birdscope 13).
Removable Nest Cups: You can make removable nest cup holders from small, low square plastic freezer containers (package of five available at Wal-Mart for less than $2.00). Drill drainage holes in the bottom. Of course check the interior floor dimensions of your box prior to purchase. (Thanks to Duane Rice for this tip.) You can also use old strawberry baskets.
Tree Swallow nests: I leave Tree Swallow nests in place for 1-2 weeks before cleaning boxes, in case they might be reused for a (rare) second brood. Used Tree Swallow nests are usually pretty gross, as adults stop removing fecal sacs at least four days before babies fledge, and may contain lots of bird mites so I usually avoid touching them with bare hands, and use a plastic bag to remove them.
Gilbertson boxes: Since the base detaches from the roof, you can keep a spare and just pop on a clean bottom and then clean out the used one at your convenience.
Hanging Box: if you have a spare, replace the dirty box with a clean one. Take the dirty one home, dump the contents, hose it down, scrub and rinse.
Note: One study showed no significant effect of cleaning or not cleaning out old nests during breeding season on the chance of nesting attempts or numbers of nestlings fledged. (Gowaty and Plissner 1997)
Mouths are open. Eyes are closed. Hints of fuzz where feathers
will grow are visible. How do such ungainly, scrawny little creatures
ever acquire such phenomenal beauty?
- Shirl Brunnel, I Hear Bluebirds, 1984
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