Bird Houses and Nest Boxes

A feeder gives birds a meal. A nest box gives them somewhere to raise a family — and that raises the stakes considerably, because a badly built or badly sited box does not simply go unused. It becomes a trap: wrong hole size lets in the aggressive species that kill nestlings, no predator guard invites raccoons and snakes, no ventilation cooks a brood in July.

So this section is unusually specific about numbers. Entrance hole diameters are given to the sixteenth of an inch because that precision is the entire mechanism — an inch and a half admits an eastern bluebird and excludes a starling, and a hole enlarged by a quarter inch undoes that protection completely. Floor dimensions, mounting height, facing direction and spacing between boxes get the same treatment.

One rule worth knowing before you buy anything: a nest box should not have a perch. Cavity-nesting birds never need one — they grip the entrance directly — while a perch gives house sparrows a place to sit and harass, and gives predators a handhold. A perch on a birdhouse is decoration for humans, sold at the birds' expense.

• Bluebird House Placement: Height, Direction and Spacing

  Where to put a bluebird house — mounting height, which way the entrance faces, box spacing, and the paired-box trick that settles tree swallow fights.

• Nest Box Hole Sizes and Dimensions by Species

  Entrance diameter is the whole mechanism: 1 1/2 in for eastern bluebirds, 1 9/16 in for mountain. A sourced nest box dimensions chart for 14 species.

• Best Bluebird Houses and Nest Boxes for Eastern Bluebirds

  Hole diameter decides whether bluebirds nest or starlings take over. The nest box standard explained, plus five boxes worth buying and who each one is wrong for.

• Best Owl Nest Boxes: Screech, Barn and Barred

  Screech, barn and barred owls need completely different boxes. Hole size, floor, mounting height and habitat compared — plus why most owl boxes stay empty.

• Best Purple Martin Houses, Gourd Racks and Poles

  Purple martins east of the Rockies nest almost only in housing people put up. The gourd racks, aluminum houses and telescoping poles that actually get a colony.

• Bluebird House Predator Guards and Sparrow Control

  What actually stops raccoons, snakes, cats, wrens and house sparrows at a nest box — baffle sizes that work, and the honest limits of every guard.