House Hunting: What a Bluebird Looks For in a Home
In this science project, I attempted to answer the question, "What are the elements of a bluebird's habitat?" In response, I monitored bluebird boxes for one season (spring through summer) at Wye Island Natural Resource Management Area. Approximately 50 bluebird boxes exist in various areas on the island. While monitoring the bluebird boxes, I looked for the presence of a bluebird nest, eggs, and bluebird young. Occasionally, there would be a nest of another specie of bird, such as a house sparrow, an enemy of the bluebird. I destroyed these nests. At the end of the season, I measured bluebird box height from the ground, direction each faced, and distance of each box from a field, tree, forest, water, power lines, and a road. I obtained data of previous seasons from the Wye Island resident ranger, Ranger Dave Davis. I sorted all of my data into spreadsheets and graphs. From this, I determined that the key elements of an attractive bluebird habitat were water and open fields.
Investigation: What are the elements of a bluebird's habitat?
The eastern bluebird (sialia sialis Linnaeus) is a small blue bird with a light brown color on its breast. Its normal height ranges from 5-1/4 to 7 inches when it is an adult.
The eastern bluebird eggs are pale blue and sometimes white. The female bluebird mostly lays four to five eggs, but sometimes they can lay as little as three or as many as seven eggs. The female eastern bluebird performs most of the incubation for her soon-to-be young. Generally, this period lasts about 12 to 16 days.
When the egg hatches, the bluebird young are born. At this stage in their life, they cannot see. Within four to five days, they grow some feathers and can see. They then learn to fly by flexing their muscles and bones in their wings. Generally, the young fledge fifteen to eighteen days after birth.
The eastern bluebird's adult diet consists of insects, especially grasshoppers, crickets, katydids, beetles, earthworms, spiders, millipedes, centipedes, sow bugs, and snails. The adult also eats fruits from dogwoods, hawthorn, and wild grape in warm weather months, and sumac and hackberry seeds in winter months. Also, adult eastern bluebirds digest fruits, such as blackberries, bayberries, honeysuckle, Virginia creeper, red cedar, and pokeberries. The young eastern bluebirds' diet includes small tender insects from their hatching and larger insects as they mature.
In the spring and summer, these bluebirds live east of the Rocky Mountains, southern Canada to the states bordering the Gulf of Mexico. They can also be found in the southeast, from Arizona to Nicaragua. In the winter, the eastern bluebird is found in southern New England, west to New Mexico and south to Mexico.
Their nest is often found in a woodpecker excavated cavity, in a loose cup of dry grass, weed stems, pine needles, twigs, and sometimes with hair or feathers. Eastern bluebirds usually nest low to the ground, about two to twenty feet. Their nests are found on farmlands, orchards, open woodlands, and sparse trees on mountain slopes. According to the Northern Prairie Research Center, eastern bluebirds prefer a complex of open, low-growing grassy fields, either mowed or growing freely. The bluebird also prefers widely scattered trees, berry-producing shrubs and vines, and snags. They perch from trees, shrubs, utility wires, telephone poles, or fence posts.
In the past, the eastern bluebird population declined because of competition for nests or cavity holes with more dominant species. Some dominant species are the blowfly, a flying insect that flies into the bluebird nest and infests it with diseases that kill the young, and the male house sparrow. The house sparrow attacks the adult bluebird and kills it. This harmful bird also kicks the bluebird eggs out of the nesting box and sometimes builds its nest over the eggs. Luckily, over the years the population has risen because of bluebird trails and their monitors. The monitors clean out the boxes every ten to fourteen days, except when it is about time for the young to fledge. If the monitor finds a house sparrow nest in a blue bird box, the monitor cleans it out. If there are house sparrow eggs in the nest, the monitor destroys these eggs by simply crunching them. If house sparrow young are found in the nest, the monitor must place them in a plastic bag and suffocate them. By performing all these steps, the bluebird has a greater chance of living and growing.