Severe weather, destruction of nesting habitat, and heavy competition with sparrows and starlings have caused a decline in the nations bluebird population. Although the pressure is not as drastic in Texas as in the North and East, this beautiful member of the thrush family needs a helping hand.
Three species of bluebirds – eastern, western, and mountain – make their homes in Texas during various times of the year. All of them are close in size, 6-1/2 to 7-1/2 inches, and weigh about one ounce.
Most common and widespread is the eastern bluebird, Sialia sialis. Although it is considered a partial migrant, it winters throughout most of Texas, except the Trans-Pecos. Almost anywhere, except the treeless prairies and heavily wooded forests, is suitable to this particular bird's needs.
The male has a bright blue back, rusty breast and throat, and white belly and undertail area. Its beautiful coloring caused the famous American writer Henry David Thoreau to say that the bird carries the sky on its back. American naturalist John Burrows observed that it also has the warm reddish-brown of the earth on its breast. Coloration of the female is much duller and paler. The young, unlike adults, have mouse-gray backs and the white speckled breasts so characteristic of thrushes. Only while they are young do these birds display their relationship to the thrush family in their coloration. A tinge of dull blue in the wings and tail give a hint of the bright colors they will wear one day.
When perching, this species appears dumpy and round-shouldered. Flight is considered more or less irregular unless the bird is traveling long distances. Short flights usually are not at a great height. During courtship the male ascends fifty to one hundred feet and then floats down to flutter around the female. He may even offer her food as he woos her with songs and tries to convince her to examine the nest site he has chosen. Finally she flies into the cavity and accepts it and the male. After lining it with grass, she lays four to six light blue eggs. Most, if not all, of the incubation during the required twelve-day period is done by the female. Both parents feed the nestlings, but again, the female does the larger share. However, when the young become fledglings and are able to leave the nest, the male takes over so the female can prepare the nest for a second brood. The male continues to feed the fledglings while teaching them to feed themselves. Sometimes young from the first brood help the parents feed the second brood.
About three-fourths of bluebirds' diet consists of insects such as beetles, grasshoppers, and caterpillars. Berries and other fruit make up the rest of their menu. Food preferences make the bluebird one of those species considered beneficial to people.
The western bluebird, Sialia mexicana, is very similar to the eastern except the male's throat is blue and he has a rusty patch on his back. Females are duller than the males and have a whitish throat. This species winters in the Trans-Pecos and breeds in the Guadalupe Mountains.
Except for its whitish belly, the mountain bluebird, Sialis currucoides, is a beautiful turquoise blue. No red appears on either the male or the female. In fall and winter the male's plumage shows touches of dull brown, which is the predominant year-round color of the female. Her drab coloring is relieved only by bluish markings on her rump, tail, and wings. The mountain bluebird, which winters in the western two-thirds of Texas, has a straighter, less hunched posture than the other bluebirds.
All species of bluebirds are cavity nesters, which means they nest in holes in trees, shrubs, fence posts, and bird-houses. With a bit of interior remodeling, they can convert abandoned woodpecker holes into comfortable nests. Chip-strewn floors may be all right for hardy woodpeckers, but a soft grass lining must be added for the more delicate young bluebirds.
At one time there were plenty of natural nesting sites for the "blue robin," a name given the bird by early settlers because of its reddish breast. Its preference for sites bordering open areas was met as the pioneers cleared forest lands for farming. The holes in the posts and rails of the wooden fences they built provided additional nesting places and the bluebird's population grew.
Their first efforts benefited the bird, but later actions were not so kind. When early settlers imported the English house sparrow and the European starling, both cavity nesting birds, they brought to America two species that are in direct competition with the bluebird for available nesting sites. Since sparrows and starlings are extremely aggressive, the gentle bluebird often lost out to its foreign competitors. Non-migrating sparrows contested the bluebird's rights to live in cities and towns in their northern range by being well established in all available housing when the bluebirds returned from their southern migration. There was nothing the bluebirds could do but move to the country. Fortunately for them, sparrows seldom use abandoned woodpecker holes or natural cavities in decaying trees as homes.
Changing lifestyles also brought problems for the bluebird. As small farms were consolidated into larger, more profitable agricultural complexes, thousands of miles of hole-riddled wooden fences were eliminated. Metal fence posts often replaced wooden ones that had provided nest sites along our roadsides. Invention of the chainsaw did not help the bluebird either. These efficient machines made it possible for landowners to cut down old, unsightly, cavity-filled trees from pastures and fencerows, thereby removing natural bluebird housing.
Severe weather also takes its toll of the brightly colored birds. Although the bluebird is an early migrant, it is not a hardy bird. Prematurely warm weather may draw flocks of them north too soon, and then they freeze when cold weather returns.
With everything working against them, it is a wonder there are any blue-birds left at all. Noticing a decline in the birds' numbers, concerned conservationists launched several campaigns to provide artificial housing for the birds. Results have been very good, especially when the houses have been placed outside the city limits or in parks. In some areas, bluebird trails have been established on rural roads. The bluebird houses are attached to fence posts or trees and spaced no closer than 200 feet nor more than a half-mile apart along the roads for miles. One man in Illinois in one season put 102 houses along 43 miles of road near his home. The world's longest bluebird trail stretches through Manitoba and Saskatchewan in Canada. Its 7000 nesting boxes cover about 2,000 miles of roadways. More than 8,000 young bluebirds and 15,000 tree swallows, a species which also finds bluebird houses to its liking, were raised in these Canadian nests in one year.
When bluebirds are present, they adapt quickly to the artificial nesting cavities and even seem to prefer them to natural ones. For those of you who would like to help the bluebirds, here are some instructions for building their houses. Whether the house design is plain or fancy makes no difference to the birds, but there are some basic requirements that must be met.
First, and very important, is the size of the entrance hole. It should be no larger than 1-1/2 inches in diameter and should be located so the lower edge of the hole is between 4 and 5-1/2 inches from the bottom of the house. If the hole is smaller than the prescribed size, the bluebird cannot enter. If the hole is placed too low, there isn't enough space below it for nesting material; however, a hole placed too high could prevent the nestlings from reaching the opening to the world of flight. No perch or landing platform should be attached beneath the entrance hole. Such accessories attract sparrows and discourage bluebirds.
Floor space may vary from an eight-inch square to a less spacious four-inch square. Trim off the four corners slightly or drill a half-inch hole in each one to provide floor drainage. Recommended side height is eight inches, but it can be taller as long as the entrance hole spacing is correct. For ventilation, drill four one-fourth-inch holes in each side about an inch below the roofline, or allow the sides to be one-fourth inch shorter than the front and back to create a crack between the roof and sides. The front, roof, or bottom should be hinged in some manner so the house can be cleaned before each nesting season. The house should not be cleaned between the first and second brood in one season. Color has little to do with acceptance or rejection by nesters, but if paint or stain is applied, it should be confined to the outside. Hot sun and treated interiors can combine to create noxious fumes capable of killing nestlings.
Bluebird houses should be hung so they will not swing in the breeze. For best results, attach them firmly to a post or tree at least five feet from the ground in open areas. Bluebirds nest successfully in old fence posts at heights of two or three feet, but they are not as likely to attract predators in these natural cavities as in man-made houses because their fence posts look like hundreds of other unoccupied fence posts. To prevent climbing predators from reaching the nest, it may be necessary to add a metal shield below the house. Greased metal poles also help to discourage predators. Wherever you put your birdhouse, make sure no overhanging branches or foliage prevent the birds from flying directly to the entrance. Some birders insist that the entrance face south, but others claim the house may face any point on the compass.
Although the 1-1/2-inch entrance hole excludes starlings, sparrows have no trouble entering. If a sparrow lays claim to your bluebird house before a bluebird is attracted, remove the sparrow's nest as quickly as it is built. This may have to be repeated several times before the nesting sparrow gives up and moves to another location. Only with your help will the mild-mannered bluebird be able to compete with the sparrow. Your efforts, whether you build one or a dozen bluebird houses, will help this bird compete for nesting space. Wouldn't it be tragic if the lack of housing wiped this beautiful song-bird from the face of the earth?
Build a Bluebird House
- 1 x 10-inch lumber–33 inches.
- 6'/2 inches of '/2-inch wood dowel or metal hinge.
- One 1-1/2-inch wood screw with washer.
- 20 to 25 l'/2 to P/t-inch nails.
- Wire or ring-shank nails to attach box to post.
- Dimensions given are for 3/4-inch thick lumber.
- Make entrance hole precisely l-1/2 inches in diameter and l-1/4 inches from the top.
- Provide space between top and sides for ventilation.
- If possible, use 1-3/4-inch galvanized siding nails or aluminum nails.
- Round comers on bottom of box for drainage, and recess bottom 1/4-inch.
- Roughen inside of front board by making notches with a saw or holes with an awl or drill, to assist young in climbing to entrance hole.
- Top of the box should be attached at the back by a 1/2-inch wooden dowel or metal hinge, and in front by a 1-1/2-inch wood screw to facilitate easy opening for inspection and cleaning.
- Drill two or three holes in the back panel of the box above and below the enclosure, to aid in quick, easy attachment to pole or post.
- Do not add any type of perch to the box; it will only serve to attract sparrows.
Site selection is the single most important step in having a successful bluebird program. Bluebirds utilize only a very specific type of habitat for nesting and only rarely will deviate from it. In general, bluebirds prefer open areas with scattered trees where the ground is not covered with tall undergrowth.
There are three general areas that should be avoided when selecting a nest site:
- Avoid placing nest boxes in towns or within the immediate area of farm yards. House sparrows invariably will occupy every such nest box.
- Do not place boxes in heavy timber. Bluebirds prefer sites associated with timber, but more at the edge of a clearing rather than in the timber stand itself.
- Do not place boxes in or near areas of widespread insecticide use. Bluebirds feed almost entirely on insects during the nesting season.
Installation and Maintenance
- Place boxes at 150- to 200-yard intervals.
- Mount boxes about five to seven feet above ground level. Fence posts make excellent mounting sites.
- Clean boxes as soon as possible after a successful hatch. Bluebirds will not utilize the same nest box unless it is cleaned.
1989 – Bluebirds: Introducing Birds to Young Naturalists. The Louise Lindsey Merrick Texas Environment Series, No. 9, pp. 24-27. Texas A&M University Press, College Station.