Because bats enter and exit roosts rapidly, owls typically need to watch from a nearby perch to be successful. This may explain why purple martins and many bats prefer house locations in open areas away from branches and other potential perches for birds of prey. Mounting evidence suggests that bats prefer houses at least 20 feet from potential owl perches, a problem most often encountered when houses are mounted on trees. Tree-mounted houses are undeniably more vulnerable to predators than are those mounted on buildings or poles. Houses located in open areas, but within 20-50 feet of river, lake, field, or yard edges seem most attractive to bats.
Snakes are most troublesome in warm climates.
While they typically cannot climb the side of a smooth building, they are expert climbers of trees and poles. Smaller baffles may work fine if local snakes are not large. Climbing raccoons can also be foiled by a snake guard placed at least three to four feet above ground. Cat problems can be reduced by placing houses between 12 and 20 feet above ground on buildings or poles. Cat predation is usually the worst when young bats, especially Mexican free-tails, are learning to fly.