To Clean Or Not To Clean Your Nest Box?

Photo © Steven Liffmann

By Anita Tendler, Cornell Class of 2019

Prior to the breeding season, we make sure that our nest boxes are ready for their future occupants. As the season progresses, we watch the naked hatchlings grow and develop into fully-feathered fledglings. Once the breeding season comes to a close, our nest boxes are abandoned and the leftover nesting material remains, which leaves the question, “What should be done with old nests?”

Nest boxes vs natural cavities

Eastern Bluebirds In A Tree Cavity
Eastern Bluebirds In A Tree Cavity

In natural cavities, birds often must deal with old nesting material that is already present.

Nest selection of natural cavities is quite different in comparison to our handy nest boxes. With a finite number of natural cavities to choose from, most birds can’t afford to be too picky. Birds often choose to reuse successful natural cavities because constructing a nest from scratch requires critical and limited time and energy. However, the threat of ectoparasites (e.g. mites, blowfly larvae) from the old nesting material can also act as a strong deterrent for cavity selection. With most birds not having the option to be choosy with their nest site selection, birds like the Eastern Bluebird simply build atop old nesting material if alternative cavities aren’t available.

Nest boxes provide cavity-nesting species the option to choose among several nest sites. As well-constructed as some nest boxes might be, they are not immune to ectoparasites, the presence of which can deter some birds from occupying a nest box.

Does removing old nests mean fewer ectoparasites?

Some birds have adapted to cope with ectoparasites, so cleaning out your nest box may not have any impact on whether they occupy it. Male House Wrens, for example, clean out the old nesting material between clutches, essentially doing the job for you.

House Wren Readying The Nest
House Wren Readying The Nest

Male House Wrens remove old nesting material between clutches.

To measure whether human intervention was helpful, researchers in Illinois removed old nesting material from some nest boxes that they knew successfully reared fledglings in the prior breeding season (Pacejka and Thompson 1996). With the other boxes left for the House Wrens to clean, the researchers conducted a mite count to determine if there was a perceptible difference. They found that there was no real difference, so regardless of who, or what, cleans out your nest box, mites will still be there.

Not all birds clean house

Bluebirds do not remove old nesting material, rather they simply build over an existing nest. If you do not clean out your nest box, it may become filled to the brim with old nesting material. This can potentially leave the new nest dangerously close to the entrance hole, where predators can easily reach it.

Eastern Bluebird Eggs
Eastern Bluebird Eggs

Some bluebirds prefer a clean nest box, but it depends on location.

To learn whether removing old nests influenced Eastern Bluebird nest box occupancy, a team of researchers in North Carolina erected 100 nest boxes. After a successful first clutch, they cleaned out half and left the others as is. When the bluebirds were left to make a choice to re-nest in a box with a positive association or to avoid ectoparasites, a whopping 71% of them them chose to move to a clean nest box (Stanback and Dervan 2001).

So that means you should clean your nest boxes, right? As compelling as these results are, it’s important to remember that this is situation-dependent. Interestingly, opposite conclusions were reached in a Kentucky study that found that Eastern Bluebirds in that state preferred nest boxes with old nests in them (Davis et al. 1994). There, parasitic wasps kill blowfly pupae over the winter; therefore, removing old nesting material may actually compromise this natural process.

To clean or not to clean? It depends…

Cleaning out your nest box is your choice, as nest site selection varies among cavity-nesting species. When making your decision, feel free to weigh the pros and cons, taking into consideration individual species preference and ectoparasite abundance. If you’re hoping to attract House Wrens to your nest box, don’t worry, they’ve got it covered. But, Eastern Bluebirds are a bit tricky. Depending on where you are, cleaning out your nest box may either invite or deter them.

A Mouse's House
A Mouse's House

Whether you decide to clean out your nest box at the end of the breeding season or not, don’t forget that leftover nesting materials make the perfect home for small mammals. If mice occupy nest boxes, you should definitely clean the boxes in the spring by removing nest material and washing with a soapy solution. Take precaution and wear gloves and a mask when removing rodent nests; they are far less fastidious than birds.


References:

  • Davis, W. H., P. J. Kalisz, and R. J. Wells. 1994. Eastern bluebirds prefer boxes containing old nests (Preferencia en Sialia sialis por cajas que contienen nidos viejos). Journal of Field Ornithology 65(2):250–253.
  • Pacejka, A. J., and C. F. Thompson. 1996. Does removal of old nests from nestboxes by researchers affect mite populations in subsequent nests of house wrens? Journal of Field Ornithology 67(4):558–64.
  • Stanback, M. T., and A. A. Dervan. 2001. Within-season nest-site fidelity in eastern bluebirds: disentangling effects of nest success and parasite avoidance. The Auk 118(3):743.

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10 Comments

  1. Kevin Holladay says:

    In northern New Mexico we are close to the epicenter of the country’s hotspot for hanta virus. Deer mice, Peromyscus, are the main vector for this virus….great reason to clean out nest boxes every year for Western and Mountain Bluebirds.

  2. Barbara Walker says:

    I’ve been told other knowledgeable Bluebird enthusiasts that it’s important to remove the old nest because if a new nest is built on top of the old one the babies and parents become vulnerable to predators, being closer to the access hole.

    Also it’s easier to see what sort of bird is rebuilding if you start with a clean box.

  3. bpsperry says:

    Just what does cleaning out a nest box mean? Merely emptying it of nesting material or is there a need to “wash” it?

  4. Kevin Corwin says:

    I monitor a line of nestboxes about 30 miles south of Denver, they get Mountain Bluebirds and Tree Swallows. I check them weekly, and when a bluebird nest fledges the female quickly builds a new cup (not an entirely new nest structure) on top of the old flattened one and has already started laying the second set of eggs before my next weekly monitoring trip. The Tree Swallows nest much later than the bluebirds and only once each season.

  5. Janet K says:

    Thank you for this article. I’ve wondered if blue blue birds would re-use their nests. We get blue birds and chickadees in our 8 nest boxes. They make very different kinds of nests. I’ve assumed that a bluebird would not move into a box with an existing chickadee nest. I’ve always cleaned them out so that all boxes are equal in the spring. I usually leave the nests until late January in case someone wants to use it for cold weather shelter. So far we’ve not had any issues with mice moving in.

  6. George Kaye says:

    Interesting blogs about cleaning out nestboxes and predator guard effectiveness!
    I monitor about 75 nest boxes in Franklin NC, most of which are near the Little Tennessee River. A serious “predator” problem I deal with is ants. They love to move into the boxes with their own eggs. I believe I have no choice but to get rid of the nests when nesting season is over. Even during nesting season, when the birds have fledged, I get rid of the nest so the next bird will not have to build a new nest on an ant colony.
    I obtained some diatomaceous earth to sprinkle on the nestbox floor nest spring to see if this helps. Anyone have any experience with diatomaceous earth?

    • Robyn Bailey says:

      Hi George, we hear you about the ants! Fire ants, especially, can prey on nestlings. NestWatcher Tara T. in Florida shares her ant-proofing tips in this years’ annual report: “In the Southeast, fire ants
      can be a serious problem. We have caulked the small space between the predator guards and the posts, and just before our birds begin laying, we go out and spray a few inches of the post just under the guard with ant spray. The caulk keeps rain from washing it away and it has proven to be effective at saving the nestlings from the ants.”

  7. Annie and David says:

    Hi Fellow NestWatchers,
    We have had a Western Bluebird box with guard for a few years and every year the first clutch is successful. However, the second clutch never has survived. We go to clean the box out and for tree years in a row there are desiccated babies left in the box. Does anyone know what is wrong? Should we shut up the box after the first clutch has fledged?

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