There are several factors to keep in mind. The location should fit the habitat needs of the species you are attempting to attract, including the surrounding vegetation, height of the box above the ground, and appropriate shelter and cover for fledglings and the availability of food and water. Regular monitoring of each nestbox is recommended to keep an eye on the developing birds. Contrary to what most people believe, approaching or handling the nestlings will not cause them to be abandoned by their parents. However, handling should not be excessive and only when necessary, such as removing blowfly larvae from the young birds.
Blowflies are surface parasites that feed on blood.
A heavy infestation can have a serious impact on the developing birds. Handling should be avoided at key stages, such as egg laying, the early incubation period and closer to fledging. Nestboxes should be inspected at the end of the winter and before the nesting season gets underway. There is more than one school of thought regarding whether old nests should be removed. The conventional wisdom has been that nestboxes should be cleaned out before new birds are allowed to use them.