You can definitely clean out a nest box after the fledglings leave—but don’t clean out nests.
Why shouldn’t you clean out a used nest? Most birds don’t reuse their old nests, no matter how clean they are. They typically build a new nest in a new location for each clutch. This reduces the prevalence of parasites—mites and lice lay eggs in nest materials, producing a whole batch of young parasites that would have a head start in attacking a new set of nestlings. Building a new nest in a new location also means predators are less likely to find the nest site before the young birds fledge.
However, for nest boxes or birdhouses, NestWatch suggests cleaning out the box at the end of the season. This isn’t absolutely necessary; often birds will clean it out themselves, but you can lend them a helping hand.
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