Challis-Yankee Fork Ranger District - Mtn. Bluebird

Homes for Idaho's Bluebirds

The Housing Shortage

Early each spring, bluebirds return to a snowy Idaho seeking tree cavities for nesting. But nesting trees have become so scarce that some bluebirds never find homes.

Many trees with suitable nesting holes have been cut for firewood or cleared to make way for businesses and homes. Remaining nest cavities are often taken by the non-native European starling and house sparrow, both bullies compared with gentle bluebirds.

Man-made nest boxes help to fill the shortage of natural nest sites. Many Idahoans have already discovered the fun and satisfaction that comes from sawing a board, hammering it into a box, placing it, outdoors, then finding it filled with a family of bluebirds. Lots of bird-loving clubs and families make it a group project.

A Bit About Bluebirds

Two species of bluebirds live in Idaho- the western bluebird and the mountain bluebird, our state bird. The mountain bluebird is larger than the western bluebird, and both are slightly smaller than robins.

bluebirdThe male mountain bluebird has a bright blue back, and is paler blue below. Its belly is whitish. The female is grayish brown with a trace of blue on wings, rump and tail.

The male western bluebird has dark-blue head, wings and tail. Its breast and back are rusty red. The female is brownish with a rust- colored breast.

Bluebirds live throughout Idaho in high desert juniper and mahogany stands, meadows in forested areas, mountain valleys and open ridges in mountainous regions. Generally, they live at elevations of 4,000 feet and higher. Bluebirds are ground feeders, with grasshoppers a dietary favorite.

Bluebirds arrive in Idaho from wintering grounds by late February or early March. Nest building begins in April. Because the bluebird bill is not suited for digging nest cavities, bluebirds make their nests in existing cavities, excavated by woodpeckers and other animals. Bluebirds make nests from grass, fine strips of bark and sometimes pine needles.

Egg laying generally begins in early May. After being incubated about 14 days, the 4-6 blue eggs hatch. Until the young bird leave the nest 18 to 21 days later, both parents feed the young with insects. During good years, bluebirds may build two nests and lay two clutches. Young birds from the first brood sometimes help their parents feed the second brood.

Bluebirds migrate south in September or early October.

Placing the Nest Box

Secure boxes to wooden or metal posts or to tree trunks in open country with scattered trees. Boxes should face and be within 50 feet of a tree, shrub or post where fledglings can perch after their first flight.

Protect boxes from prevailing winds and the hot afternoon sun by mounting them on the lee side of mounting posts, never facing south. Placing the boxes out of sight of roads can reduce vandalism.

Set boxes about five feet above the ground for easy maintenance. Placed lower than three feet, they are in easy reach of predators. If cattle are in the area or if molestation by humans may be a problem, 8-foot-high boxes may be preferred. You will need a 5-foot aluminum ladder to reach them for cleaning.

Bluebirds are territorial, so boxes should be placed at least 100 yards apart. Some authorities recommend a distance of as much as 1/4 mile between mountain bluebird houses, especially in areas where there are few trees.

Wrens, swallows and house sparrows will all use bluebird boxes, but proper nest box placement helps reserve the boxes for bluebirds. Avoiding brushy areas helps keep wrens out. Keeping houses away from buildings reduces the chances of house sparrows nesting. If you discover house sparrows using a box, remove their nest. Nests may have to be removed every few days for a week or more before the sparrows vacate permanently.

Swallows are less likely to nest in boxes distant from water. If tree swallows become a problem, try placing boxes in pairs. The swallows, which like bluebirds are territorial, will nest in one box, leaving the second for bluebirds.

In areas where cattle graze, pile rocks around the base of nest box posts so cattle can't rub against them.

Try to place boxes by the end of February. But because bluebirds may move into boxes as late as mid-May, placement in early spring may not be too late.

Keeping Predators Out

A 3-foot-long collar of galvanized metal placed around the box support helps keep predators such as raccoons out of the nest box. A thick coating of automobile chassis grease slathered on metal posts also frustrates climbing predators. Apply the grease to the 12 inches of post directly below the box.1

Maintaining the Nest Box

September is a good time to clean nest boxes. Remove all debris and scrape the interior walls with a putty knife. In late March or early April, check the boxes again and make emergency repairs.

If you inspect boxes between broods, remove used nest material. Dead birds discovered in a nest should be removed, even when the box is occupied.

Keeping Track

In late May or early June, check the boxes for use. Occupied boxes should be opened quietly and carefully. Boxes containing young birds more than 13 days old should be opened with great care. If disturbed too much, these young birds may leave the nest before they are ready.

Check sheets can be used to record the species using each box, the number of eggs and/or young and other items of interest. Use a separate sheet or index card for each box. If a box is not used for several years, move it to a new location. If you find animals other than bluebirds raising young in the boxes, allow them to finish, then move the box.

Outside links with pictures and descriptions of Mountain Bluebirds.

This information is reprinted from a pamphlet that was made possible from donations to the Dory Keating Memorial Fund, the Idaho State Conservation Officers Association, and the Idaho Department of Fish and Game Nongame Wildlife Program.

Idaho Nongame Wildlife Program
Idaho Department of Fish and Game
P.O. Box 25
Boise ID 83707