Northern Prairie Wildlife Research Center
Nest boxes should be constructed of a weather-resistant wood; cedar is often recommended. The wood can be painted or stained, but only on the outside surface. The entrance hole should be 1.5 inches in diameter. Numerous nest box designs have been used with success; figure 1 provides one example. A good method of assisting fledglings in their climb from the nest to the entrance hole is to roughen up the inside wood surface under the hole with a chisel. The lid or one side of the box should open to facilitate monitoring and cleaning. Three or four 1/4 inch drain holes should be drilled into the box bottom. Ventilation and shade requirements are met by overhanging roofs and construction designs described in figure 1. All bluebird boxes should be fitted with a galvanized sheet metal predator guard (see fig. 2). The predator guard should be placed on the pole 6 to 12 inches below the bottom of the box. Also, to help deter predation, an even coating of non-drying crankcase grease or carnauba wax can be applied to the pole from the ground to six inches below the box.
Place eastern bluebird nest boxes in open grassy areas that are accompanied by widely scattered trees and shrubs. Open areas are preferred, as placement of boxes in or near areas thick with brush and woody vegetation likely will result in habitation of many boxes by house wrens. Boxes should be placed at least 100 yards apart to accommodate individual territories established by nesting pairs during the breeding season. Boxes should be placed well away from buildings because of the high concentration of house sparrows generally found near human habitations. Mount nest boxes 4 to 6 feet above the ground on a metal or wooden post equipped with a predator guard as shown in figure 2. Research has shown that placing boxes low to the ground, at 4 to 5 feet, may help to deter sparrows from inhabiting them. Boxes should face away from prevailing winds and rain and be placed in a location that will enable the box to receive a fair amount of sunlight. Ideally, a tree or shrub should be located 25 to 100 feet away in front of a box entrance. This will provide a perch for foraging adults and fledglings will use this cover on their first flight out of the box. Nest boxes should be located far away from any area that is heavily treated with pesticides or herbicides. Overall, one should attempt to accommodate the natural nesting instincts and requirements of the birds while still allowing for weekly monitoring during the breeding season.
The side view shows a guard affixed to a nest box post. This is done by overlapping the edges of the 60-degree wedge to the shown dotted line. Bolts or screws are then used to form the sheet into a cone. Fasten the guard to the post with supporting brackets. Note: 3 wooden mounting blocks can also be placed on the underside of the guard to fasten it to the post. Fasten the blocks to the guard and post with screws. The predator guard should be placed on the post so the bottom of the guard is at least 4 feet from the ground.
Before nesting boxes are erected, a maintenance, monitoring, and data collection plan should be developed to ensure program success. Unmonitored boxes may be counter-productive by helping to increase populations of exotic competitor species such as house sparrow. It is essential to erect only as many boxes as can be realistically monitored. Boxes should be monitored once a week during the breeding season (March-July). However, monitors should avoid disturbing boxes during cold, rainy, or other inclement weather that may harm nesting birds or eggs. Activity characteristic of adult nesting bluebirds includes frequent entering and exiting of the nest box with either nest materials or food, as well as adults leaving the box carrying fecal sacs for disposal. Approach nest boxes from an angle and make a slight noise to flush the female from the nest. Gently tapping on the box may cue the female to exit as well. Once the female exits, the box can be opened and its contents recorded. Boxes should not, however, be opened after the 12th day following hatching to prevent young from prematurely leaving the nest. Move away from the box at the same angle but in the opposite direction in which it was approached, keeping footsteps around the box to a minimum. This will help to reduce predation by not establishing a scent trail that results from approaching and returning from a box along the same path. Since bluebird pairs often raise more than one clutch each season, old nests should be removed from boxes after each clutch fledges. Boxes should be left out at the end of the nesting season, as they sometimes provide winter shelter for various species of birds and other wildlife. Clean nesting materials may be beneficial to wildlife using boxes in the winter and can be left in boxes at season's end. Boxes should be cleaned of all nesting materials in the spring, however, before the start of the nesting season. For Wildlife Habitat Council member organizations, the monitoring program may enroll in WHCs Nest Monitoring Program, useful in WHC's Corporate Wildlife Habitat Certification Program. Enrollment can be accomplished by contacting the WHC Nest Monitoring Program Coordinator at (301) 588-8994. Data collected using the Nest Box Data Sheet can also be sent to the North American Bluebird Society, PO. Box 74, Darlington, WI 53530, to aid in evaluating the status of the eastern bluebird throughout North America.