Nest Boxes: A Functional Habitat Enhancement

The jaunty woodpeckers rock side to side as they chisel into dead trees carving homes and seeking bugs. We hear their hearty “Ha Di Da Ha Ha. Ha Di Da Ha Ha” and are amazed at their rhythmic drumming in the spring. They are keystone species in the forest, eating lots of insects and providing habitat for other species through their activities.

Many of our fantastic forest wildlife species require cavity habitats in dead wood for reproduction and roosting cover. Over the years, however, human activities have often removed this critical habitat component. The importance of this habitat feature is now common knowledge among foresters, biologists, managers and landowners, but, recruitment and development of dead wood structure with suitable softness (from fungal action) for cavity excavation by woodpeckers, can take many years. Thus, action is sometimes needed to provide cavity habitats now.

NB_swallow on box
Providing adequate numbers of snags, standing dead trees is, of course, the best strategy, but sometimes, they simply don’t exist. Substitute cavities can be provided through creative carpentry, utilizing man-made slices of trees (boards, that is) to manufacture artificial, quasi-cavities we call “nest boxes”. (The term “bird house” is incorrect, as it implies the box will provide all of life’s requirements for the species; nope, these boxes are for nesting and, sometimes, roosting.)

Cavity Excavating Birds Come in Many Sizes

Cavity excavating birds in the Pacific Northwest come in a variety of sizes, from the massive pileated (wingspan 29”, weight 290 g) to the diminutive red breasted nuthatch (wingspan 8”, weight 10 g). Each species creates cavities that roughly match the size of the bird, and precisely provide the depth and width to enable brood rearing. Some of these attributes help with thermal regulation for the helpless young, provide room for them to grow and stretch out, and depth to resist the inevitable predators that will try to consume the delicious eggs and young. For example, flickers are about 12 inches long, and make cavities with entrance holes about 3 inches in diameter and 13 to 16 inches deep. The entrance hole is proportional to the size of the bird, and the depth is enough to keep predators from easily reaching the brood. Pileateds make appropriately enormous cavities!

Constructing cavities is a regular part of nesting and courtship behavior among the woodpeckers and the other smaller cavity excavating birds (chickadees, nuthatches). These birds will make a new cavity in most nesting seasons, and abandon the old ones when nesting is done. These abandoned cavities are prime real estate and readily sought after by a host of other species, the secondary cavity nesters. These species include many of our favorites, and will readily use man made nest boxes.NB_squirrel

Building a Nest Box

In the north Cascades town of Twisp, Washington, Patrick Hannigan has a unique business creating species-appropriate, biologically correct nest boxes out of salvaged wood from construction sites or demolitions.

“I always loved building things”, said Hannigan when I interviewed him, “and I am fascinated by birds. Construction projects always leave huge piles of scraps, and this is my way of returning this waste back into habitat.”

Patrick, who has supplied hundreds of the boxes to clients across Washington, adds:

“The species I have had use them the most include kestrels, Western bluebirds, tree and violet green swallows, saw whet owls, both mountain and black-capped chickadees, red breasted and white breasted nuthatches and wrens.”

I asked what are key elements for functional nest boxes? He listed five:

  1. Proper dimensions: that is, entrance hole size, depth to floor, and floor dimensions
  2. Proper ventilation: ¼-inch slot or holes along the top
  3. Drainage in floor to allow water out and air in to dry nesting material
  4. Door that opens to facilitate easy clean out. It is best if no tools are required for this job.
  5. Roughened interior walls to help fledglings climb out. Sometimes boxes made of smooth, planed wood become an inadvertent death trap for baby birds.

Three sizes of nest boxes are all that most small forest landowners need to consider.

  • Small: A 1 1/8” entrance hole, with a 4 ¼” square floor is just right for chickadees and wrens.
  • Medium: Swallows and bluebirds need 1 ½” entrance holes and a 5” x 5” minimum floor.
  • Large: Kestrels, small owls and squirrels need 4” holes and 17” to the bottom of the box. (Many nest box plans are available online, so check these before designing one on your own).

These three sizes will cover most of the species you may encounter on your lands (Wood duck boxes that would be placed along ponds and wetlands are larger and a special case).

Materials: Dos and Don’ts

Nest box materials can be any type of wood, but roofs need to be sturdy (and perhaps waterproofed). Avoid particle board as it will crumble in a short time. Pine and fir work fine. Do not paint on the inside of the box but the birds don’t care if the outside is painted.

Hannigan also cautions against using metal roofs or sides. These can become “bird microwaves” and when the weather warms can have the unintended consequence of killing the same birds the structure was meant to help. And ornamental “bird houses” with random hole sizes or inadequate interiors, made to be cute and not functional (sorry to those clever crafty folks!); bad bad bad. “These are made for people, not birds and can even be harmful.”

Placing Nest Boxes

Hannigan recommends focusing on forest edges for the most nesting opportunities. As to placement, think vertical. Small birds will be lower in the canopy, larger species prefer to be higher. Smaller boxes can be placed at eye level, where they are easy to clean out. Place larger boxes for owls or kestrels at least 12 to 15 feet high, a comfortable height using a standard ladder. Make sure the entrance has a clear flight line not too encumbered by overhanging branches. NB_lostLake-OKcountyHannigan recommends placing your first boxes where they are near your home, in normal sight lines so you can see and appreciate what species are using them. Boxes can be placed close together for swallows, or spread around for other species. See if they are being used in a given season and move them if they are not.

Caution should be noted with bluebird style or kestrel boxes near human habitation. These can provide habitat for aggressive starlings or house sparrows. In normal forest settings, however, these species are rarely a problem.

Nest boxes are one of my favorite tools for enhancing habitat on forest lands. Why? Because they work, they are something we can DO, and we get to experience firsthand some of the wonderful wildlife in our forests. Nest boxes are an excellent tool to help small forest landowners provide habitat for the many wildlife species we value so much; but, as with any tool, they need to be applied properly, with careful construction and placement.

Please contact me with questions, comments, pictures or stories about your nest boxes.

By Ken Bevis, DNR Stewardship Wildlife Biologist, ken.bevis@dnr.wa.gov