The eastern bluebird is a colorful thrush of open forest edges. It whistles its gentle, musical "chir-wi" or soft "tru-a-lly" near open grassy parks, fields, roadsides and old orchards. We often see the male, with his blue back and rusty throat and breast, perched on a telephone line or fence post. Only seven inches long, the bluebird is much smaller than its noisy blue and white woodland neighbor, the bluejay (12 inches); it is larger than the all blue, shrubland indigo bunting (five inches), and eats, behaves and nests differently from our western Iowa blue grosbeak (seven inches).
Cavities in scattered old oaks and elms, across the plains and along forest edges, were once home to the bluebird. Lacking the tools of woodpeckers and squirrels, the bluebird is a secondary tenant, waiting for these excavators to make (and then leave) suitable nest holes. Today, of course, most of these old stubs are gone, cut for fuel, farm ground, or "sightliness." Deprived of nesting sites and hunting grounds of short grasses, the bluebird needs our help.
Oh, Give me a Home, By Pat Schlarbaum
Its special observing wildlife at close range, and seeing songbirds providing for their young is especially uplifting. Iowa's diverse nesting songbird populations require many habitats to successfully nest and raise their broods...
Fall
The entire bluebird family raised by each pair usually flocks together until fall, treating us to sights of 6, or 10, or 20 bluebirds perched along a stretch of quiet roadside. Those with colder feet soon head south for the winter. Migrating bluebirds may travel as far as eastern Mexico, or stay as close as Missouri. Those bluebirds that choose to "tough out" Iowa's winter have to switch diets (from insects to small fruits and berries) and habitats (from open grasslands to more sheltered, wooded, areas).
Winter
Yes, some bluebirds do spend the winter in Iowa! While most bluebirds leave for southern states, up to a third of them stay. These are the birds that people see during Christmas bird counts before the real migrants return. They depend on fleshy seeds during cold periods when no insects are available. Red cedar, Virginia creeper, sumacs, bitterweeet, hackberry and hawthorne are all native plants that feed wintering bluebirds. Shelter from winter winds is vital, and concerned people plant windbreaks and put out insulated roosting boxes to protect winter residents.
Spring and Summer
Bluebirds return during late February into mid-April. Young birds often return to within a mile or two of the area where they hatched, and adult birds usually find the neighborhood where they successfully raised a family last year. The first males back pick out the best nesting areas, and a week of feverish inspection precedes pairing off and mate selection. Bluebirds are territorial and defend an area several hunted feet wide in order to assure their mate and offspring adequate supplies of insect food. Female bluebirds inspects several nest sites and may start several nests before finishing one within this territory. Then in early-to-mid-April they begin to lay their first clutch of about five pale blue eggs. About 3% of the bluebird eggs laid in Iowa nest boxes are white.
How Can I Help?
Habitat is most important to bluebirds, as to all our wildlife neighbors provide them open grassy areas to hunt beetles, grasshoppers and butterflies. Leave dead trees standing, if they don't endanger your house, for woodpecker (and later, bluebird) nest construction. Plant windbreaks and shelterbelts that reduce your heating bills as they protect wintering birds from savage plains' winds. Also plant some of the fruiting shrubs mentioned earlier to beautify your landscape and feed birds during tight times.
Nest Boxes provide bluebirds homes where feeding, but not nesting, habitat is available. You can construct them from plans like those found below. We developed this plan to try to provide bluebirds a nest safe from raccoons and summer heat. It was designed with the Iowa bluebird in mind and is based on bluebird nesting preferences as observed by many Iowa bluebird enthusiasts.
Boxes need not be works of art, and they are excellent "rainy day" or group activity projects. Bluebirds will use almost any cavity with a floor that is three to six inches on a side. The opening should be 1 1/2 inches wide "to exclude starlings." Be sure to make the cavity at least six or eight inches deeper than the bottom of the entrance hole to avoid 'coon predation. use screws to keep the box together longer. If you want to protect the box from weathering, use light (tan or gray) colored exterior stain or acrylic paint, but stay away from wood preservatives like "penta" (-chlorophenol)--it cannot help the tender nestlings' skin. Swinging doors, like the one in this design, make cleaning easier.
Both male and female bluebirds take turns incubating their eggs for about two weeks. Their eggs hatch almost all at once, and then the adults must being to search for insect food to fill hungry mouths. Young bluebirds grow fast, but they usually cannot fly on their own until about 20 days. (It is safest not to open the nest box after their twelfth day to prevent premature fledging and subsequent exposure or predation.) Usually, as soon as the first brood is flying and feeding on its own, the parents construct another nest of find grasses or forbs. Then in mid-June females lay their second clutch and begin another cycle of incubation, hatching and fledging. In "good" years of abundant insects and favorable weather, they may even bring off a third brood. Bluebirds are as faithful to their mates as they are to their home territories and seldom pick a new mate, unless their first nest fails or their mate dies.
A Bluebird's Enemies
Raccoons are always a problem. They live in the same forest edges and can climb almost any post or tree that supports a bluebird nest. With dexterous paws, they can even figure out how to undo latches to get at a meal of eggs or young birds. Raccoon attacks increase through the breeding season, affecting second and third nests most. The extra thickness of wood to the entrance of bluebird houses as a "raccoon guard" does not always stop these intrepid predators, and it reduces ventilation of the nest box. Extra depth in the nest box should place nest contents beyond 'coons' grasp. PVC pipe post-covers, stove pipe, metal flashing "predator guards" and disc blades may also deter raccoon predation, and their use is strongly encouraged.
Cats are also a serious and cunning predator of bluebirds. Nest boxes should be placed at least 100 yards from buildings, to avoid both marauding cats and house sparrows.
House wrens compete for nest sites with bluebirds. They will fill boxes with twigs over bluebird nests. More importantly, wrens peck or throw out bluebird eggs in an effort to drive the bluebirds away. Place bluebird boxes in the open, facing away from brush to reduce this lethal competition.
Starlings and house sparrows are cavity nesting birds imported from Europe during the late 1800s. They are extremely adaptable and compete strongly with bluebirds (and nuthatches, chickadees, tree swallows, etc.) for available nest sites. Since they are more common near buildings, keep bluebird boxes at least 100 yards away. Some research indicates that light-colored cavities are less attractive to these intruders. While open top boxes are light, they are NOT recommended--they admit so much sunlight that nestlings are killed by summer heat.
Snakes are adept at climbing most short poles to rob nests. Use the same tricks that foil 'coons and cats, and leave nest boxes open at the end of the season to keep an otherwise helpful snake from taking up residence.
Blowflies can be deadly parasites of young bluebirds. These fly larvae build up through the nesting season and attack later broods most heavily. Good nest box sanitation between nestings and at the end of the season are the best defenses (fresh air and sunlight are probably better than Lysol). Lawrence Zeleny, noted bluebird expert, recommends pyrethrin as the safest insecticide to use in the nest box, and it can be placed beneath the nest. It may also repel wasps and ants.
Bluebird Box Trails
Trails of bluebird boxes can become a delightful hobby. Just maintain, watch and enjoy the 5, 10, or 50 boxes you have erected in your neighborhood. You can appreciate the bluebirds (or tree swallows, or chickadees) as they appreciate your handiwork through the summer--and through the years. Remember, bluebirds return to their natal area and to successful nesting grounds, so you may develop quite a crowd of pretty neighbors.
If you keep notes, you should see that the number of boxes used (and bluebirds present) increases each year. When you do establish and maintain a bluebird trail, using whatever style(s) of boxes, won't you share your experiences with others? Just drop a note to the biologists at the Wildlife Research Station, 1436 255th St., Boone IA 50036, and describe your trail and its success. We will gladly send you some forms to keep records of your nests, and we will share your name and trail with other friends of the "Gems of Blue."
You might be interested in the materials, plans and information that the North American Bluebird Society puts out, also. They publish Sialia, and Dr. Zeleny's book. Write to Box 6295, Silver Spring MD 20906, about membership or books.
Eastern Bluebird House - Instructions
General Box Guidelines:
- Construct house of wood; 3/4 inch up to two inches thick.
- Place nest houses in short-grass open areas with scattered trees on its own post..
- Avoid brushy areas (wrens) and buildings (sparrows).
- Mount nest boxes four to six feet above ground, and always use predator guards.
- Orient boxes any way but north (east is best). Is there a perch in sight of the entrance?
- Get PERMISSION from every landowner before placing boxes, even on roadsides. Don't use power poles or fence line posts.
- Open, check, and clean boxes between broods and at the end of the nesting season. Plug entrance hole over winter to keep sparrows out.
- Repair boxes in February, and place new boxes in mid-March to early April (keep sparrows out!).