Bird Nestbox Spring Cleaning - Yes or No?

Excerpted from: To Clean Or Not To Clean Your Nest Box?

Pair of Eastern screech owls in cavity nest

After last seasons naked hatchlings grew and developed into fully-feathered fledglings and the breeding season comes to a close, the nest boxes are abandoned and the leftover nesting material remains. This leaves the question, “What should be done with old nests?”

Nestboxes versus Natural Cavities

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.

Controlling Ectoparasites

Bluebird perched on nestbox

Some birds have adapted to cope with ectoparasites like flies, gnats, lice and mites. 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.

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. 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 Their Nestbox

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.

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.

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. There, parasitic wasps kill blowfly pupae over the winter. Removing old nesting material may actually compromise this natural process.

To Clean or Not To Clean?

Mice in bird nestbox

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.

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 a next box, 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 as they are far less fastidious than birds.

When To Clean Nestboxes

Ideally, a bird house should be cleaned after the nesting brood has completely fledged and no longer returns to the nest. For many bird species, a single cleaning after the end of the breeding season is sufficient. In temperate regions where birds may raise multiple broods, however, the bird house can be cleaned between each new family to encourage more nesting.

How To Clean a Nextbox

Cleaning a bird nestbox

  Open the bird house or partially disassemble it if necessary for proper cleaning. Bird houses with swinging sides, hinged roofs or removable fronts are the easiest to clean quickly and thoroughly.
  Remove all old nesting material and scrape out any feces or clumped matter. This material should be disposed of in a plastic bag to prevent spreading any parasites it might harbor. Old nesting material could also be composted if desired.
  Scrub the house thoroughly with a weak bleach solution (1 part chlorine bleach to 9 parts warm water). Be sure to scrub all corners, the entrance hole and drainage and ventilation holes to remove all debris and contamination.
  Rinse the house well in clean water for several minutes to remove all traces of bleach or other chemicals so there will be no remaining harsh chemicals or fumes to affect birds.
  Dry the house thoroughly in full sun for at least several hours. This will break down any remaining chlorine and ensure there are no moist crevices for mold or mildew to grow.
  Inspect the house for loose hinges, protruding nails or screws, prominent splinters and other hazards that can injure adult or hatchling birds. Fix any issues to keep the house safe.
  Check that all ventilation and drainage holes are unobstructed. If needed, drill additional holes to provide extra ventilation or drainage to improve the house.
  Reassemble the house securely and check that all screws, hinges and joints are tight. If the house converts to a winter bird roost box, assemble it in that configuration after the breeding season ends so birds can use it for safe shelter.
  Store delicate gourds or clay bird houses for winter so they will last longer, or return wooden bird houses to their hooks or posts so they can be used as roost boxes for cold winter nights.

Further Reading:

 Beavers — Nature's Hydrologist, Part 2
 Garter Snakes — The Gardener's Friend
 Wisconsin Native Salamanders
 Goundhog or Woochuck: All The Facts
 Voles, Both The Good and The Bad

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