Bird Boxes

Hints For Attracting Birds With Nesting Boxes
By Keith Evans

Approximately 85 species of North American breeding birds select or construct a cavity for their nest. Populations of many of these species have declined in recent times as harvesting forests early in the life-cycle to avoid the "dead and dying" look and removing trees if they look deceased or dying in urban forest settings have eliminated many cavity nesting opportunities. These dead and dying trees (snags) provided the substrate for nests in the past. Nesting box programs, like the Eastern Bluebird and the Purple Martin nest box programs, have helped a few species recover. Man-made nesting boxes are primarily used by the secondary cavity-nesters -- species that select an available cavity, not a species that build their own. Cavity-nesters range in size from the chickadee to the Turkey Vulture, so a lot of choices are available for people interested in helping birds.

Computer links at this site provide the specifics for building a nesting box for the species of choice. Following are a few hints to improve your success in attracting and providing for a bird to enhance your enjoyment in watchable wildlife pursuits as well as improving the productivity of our wonderful bird diversity.

Before a nest box design is selected several options should be considered. First, what birds provide the best opportunities for your area? To make this choice, you must become familiar with the cavity-nesting birds in your area -- "area" is often a combination of geographical location, habitat types at and near the proposed nest box site, and elevation in the west. For example, a Carolina Wren would not be expected in the west and a Pygmy Nuthatch would not be expected in the southeast. Once a target species is selected based on range, habitat, and opportunity, then the correct box design can be selected. Remember, you are only providing the "nursery" the bird still needs to be close to the "kitchen" for adequate food for the adults and the young.

Placement of the box is the next decision. Birds are adaptable, so in many cases placement is not critical. The box does need to be accessible (to you) for cleaning each fall. Some species will build a new nest on top of an old nest, but for best results, the boxes should be cleaned each year after the nesting season. Other placement decisions are based on the species, the habitat and the geographical location. For example, species like the American Kestrel like nesting boxes placed approximately 20 feet high, whereas, bluebirds prefer boxes at a 4-7 foot height. My favorite backyard bird, the Black-capped Chickadee, seems to prefer a box about 15 feet high. Much has been written about the direction (North, South, East, West) the entrance hole should be directed. Personally, I haven't found the consistency needed to make a recommendation. I suggest using common sense. Generally, in southern ranges the hole should face north or east to reduce heat "loading" during hot afternoons. In northern ranges, a south facing hole might actually help keep the inhabitants warm. Boxes in heavy forest cover aren't as critical as boxes in open habitats.

There are a few nest box placement options that should be avoided. First, the entrance hole should not face a busy street or highway. The adults flying to and from the box risk being hit by a fast moving car. Second, the box should not be in a major human use area. Adult birds are reluctant to select a box in an area with lots of disturbance. If the box is selected, the adults may not have adequate opportunity to make enough feeding trips to the box to maintain healthy young. If in an urban setting, the box should be near escape cover so when the young fledge they can hide and not be eaten by a house cat before developing strong flight capabilities.

Another consideration for a successful nest box experience is the likelihood of predation. Some nests are always destroyed by predators, so complete protection is probably not practical. However some precautions are often warranted. First, be precise on the entrance hole size. Bluebirds will nest in box with a 1 9/16 inch hole -- any bigger hole will allow the European Starling to evict the bluebirds. The same is true with chickadees -- if the hole is larger than 1 1/8 inch, House Sparrow will probably be using the box. If a nest box hole is enlarged by woodpeckers or squirrels, then the front panel needs to be replaced with the correct sized hole. Other predators, such as the raccoon, squirrel, Blue Jay, and Black-billed Magpie, often require some special consideration. One box design I've seen is about 5 inches square (chickadees to bluebirds) and about 18 inches long. A baffle (2 inches high) is placed about 5 inches from the back of the box to encourage birds to nest behind the baffle, but well out of reach of a raccoon or squirrel. If snakes are a problem, a metal shield around the tree or pole holding the nest box will often be enough.

In summary, nesting box success is often related to a few simple decisions related to box size, entrance hole size, box placement, predator proofing, available feeding habitat, available escape cover, avoidance of known hazards, and luck. Locate a design of your choice and enjoy the birds.