The destruction of rodents is another service birds perform for the farmer. Rodents feed chiefly on roots, seeds, and green crops. The damage they do amounts to millions of dollars yearly. Hawks, owls, and other predatory birds are one of nature's checks upon the number of rodents. Each hawk or owl requires about three mice a day.
Owls are far more efficient than cats at clearing out a rodent-infested barn.
As humans have cut down trees and cleared land for building cities, they have destroyed many of the places that birds normally use for nesting. Fortunately, some species have learned to use human structures, like bridges and barns, as places for nest-building. Other species may need extra help from humans to find a place to nest. People who like birds often put out boxes and birdhouses that attract bluebirds, purple martins, and other species. Interest in birds and their conservation no longer needs to be justified.