Baby birds are fledging. So should you now clean out the nest boxes?

The first broods of bluebirds, Carolina wrens, and chickadees have fledged. So should we rid the nest boxes of old nest material and all its mess as soon as babies fledge?

Research says, that depends.

According to Cornell’s NestWatch.org website, “the threat of ectoparasites (e.g. mites, blowfly larvae) from the old nesting material can act as a strong deterrent for cavity selection.”

Most birds build new nests in new locations for new broods. Facing limited nest cavity options, however, some birds, especially bluebirds, may build the second (or third) nest atop the old. The downside, then, is the buildup of nest materials putting babies dangerously close to the top, within easy reach of predators.

But what if the bluebirds have a choice − empty, clean boxes or used but successful boxes? Using 100 nest boxes, researchers M.T. Stanback and A.A. Dervan (2001) cleaned half of the boxes and left the rest. “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 chose to move to a clean nest box.”

So between broods, evidence says to clean out the boxes as soon as birds fledge.

At the end of the season, however, another study by W. H. Davis and colleagues (1994) found that bluebirds “preferred nest boxes with old nest in them. There, parasitic wasps kill blowfly pupae over the winter; therefore, removing old nesting material may actually compromise this natural process.”

But note that the Davis study refers to over-winter situations. What ramifications could that have?

First, old nests in winter boxes often house small mammals, including mice. And mice are far from neat and tidy, thus calling for a soapy solution cleanup in chilly late February. Pair that complication with the fact that our resident cavity nesters--bluebirds, chickadees, Carolina wrens, titmice − nest early. They’re on territory year-round; they check out potential nest sites in mid-winter; and they grab the best cavities before migrating cavity nesters like house wrens arrive.

Mice or other small mammals occupying nest boxes in winter also means birds can’t use the nest boxes for winter roosts. The same birds that nest in cavities will use cavities for protection against bitter cold, multiple individuals of a species often huddling together for warmth.

Considering the combination of factors while weighing the pros and cons of cleaning, the answer seems obvious. Clean ‘em out. And do it after each brood fledges. Year-round. At the end of the season, remove the nesting material (car ice scraper works well). Scrub inside with a mild detergent and water. Avoid insecticides or other toxic substances.

Should we remove nests that aren’t in boxes, situated, for instance, in trees or bushes? According to NestWatch.org, “There’s no need to do any clean-up [of these nests]. Most birds don’t reuse their old nests. [Building a new nest] reduces the prevalence of nest parasites such as mites and lice. And building a new nest in a new location also means predators are less likely to find the nest site before the young birds fledge.”

Need to know more about nest boxes, how to choose, mount, and monitor them? Check out a comprehensive guide for over 60 cavity-nesting species at nestwatch.org/learn/all-about-birdhouses/.

For more information about birds and bird habitat, see Sharon Sorenson’s books How Birds Behave, Birds in the Yard Month by Month, and Planting Native to Attract Birds to Your Yard. Follow daily bird activity on Facebook at SharonSorensonBirdLady, or email her at chshsoren@gmail.com.

This article originally appeared on Evansville Courier & Press: Baby birds are fledging. So should you now clean out the nest boxes?