Squirrels may also use this box.
Suitable Nestbox Size: 24-inch by 10.5 -inch by 13-inch. No perches at the entrance holes as they would aid predators.
Floor Dimensions: 10″ x 10″ with ventilation holes (suggested 5)
Entrance Hole: 3 inches high by 4-inch wide, located about 21 above the floor
Roof: Hinged, secured with shutter hooks. Sloped down, overlapping on the sides and the front reduces exposure to rain and makes it more difficult for predators to get to the chicks or eggs.
Hardware: Best to use corrosion resistant, stainless steel and dichromate plated screws
Material to be used: Red Cedar (more durable than other wood material), rough cut boards or exterior-grade plywood at least 1/2″ thick. Unpainted.
Predator Guard: An inverted metal cone attached below the nextbox will provide some protection against predators
Mount about 4 to 10 feet up on a tree or a post
Within 1/4 mile of bodies of water (lakes or rivers) or marshes; best placed facing water or in standing water to reduce the risk of predation
For Kestrels or Owls:
Mount about 12 – 20 feet high.
Line nest box floor with some wood litter.
Take nest box down after each breeding season, and repair and sanitize before reusing.
Washington Department of Fish and Wildlife provides this excellent resource on nest management and construction: https://wdfw.wa.gov/publications/00406/wdfw00406.pdf