A study published in the Forest Ecology and Management journal has found that nest boxes have higher humidity levels, poorer insulation and a drier microclimate than natural tree cavities. Poorer insulation can effect bird health, especially in environments with an extreme climate. High humidity can dehydrate young and attract insects and/or parasites. While tree cavities naturally clean themselves of debris, the dry microclimate of nest boxes allow material to accumulate. Nest boxes do, however, provide more protection against storms that could otherwise soak a nest, and they have been documented to help increase the populations of pied flycatchers and barn owls. The research team concluded that adding nest boxes to a site without tree cavities is beneficial, but if a site already has an abundance of tree cavities, maintaining those trees is more efficient than building nest boxes since tree cavities naturally clean themselves and provide more diverse habitats that more animals, like bats, can live in.
Nest Boxes Cannot Replace Tree Cavities