by Dylan Reynolds
October 01, 2019
After decades of rapid habitat loss and competition from invasive species, one of the Chesapeake Bay’s favorite birds is filling the skies once more.
The eastern bluebird (Sialia sialis), named for its bright blue wings and back, is a year-round resident in the Bay watershed. The small, plump bird feeds primarily on insects and plays an important role on farms and gardens, eating many of the pests that damage crops. With a distinct, musical chirp and wings so brilliantly blue that they have inspired poetry, the eastern bluebird is one of the Bay’s most beloved birds.
For a long time, however, the bluebird’s future was uncertain.
Threats to the bluebird
In the mid-1900s, widespread conversion of farmland into urban housing and industrial developments meant that bluebirds were losing habitat at a rapid rate, and a nationwide increase in harmful pesticide use put the bluebird at even further risk. The greatest threat to the eastern bluebird, however, was the house sparrow.
House sparrows were first introduced into the United States in the 1800s from Europe, with the hopes that they would help farmers by preying on pests plaguing their crops. Instead, the sparrow began aggressively competing with many of the country’s native species for resources—including the eastern bluebird.
House sparrows prefer similar habitats to bluebirds, and will compete with them for their nesting spots—sometimes going so far as to drive them out of their nests or even kill them.
If driven from its nest, a bluebird may not be able to find a new one. Eastern bluebirds only build their nests in small, pre-existing cavities, often created by woodpeckers in trees. If a bluebird cannot find an adequate cavity for its nest, instead of creating a new one, it will not breed.
Faced with nesting competition and attacks from house sparrows, and widespread habitat loss from development, the eastern bluebird’s population was devastated. By 1970, the bird’s numbers were down by 92% across the country.
A miraculous comeback
In the late 1960s, public outcry over the bird’s future began to shift the winds in the bluebird’s favor. The restoration initiative began when two amateur birdwatchers from New York petitioned their local assemblyman to help pass legislation declaring the eastern bluebird the official state bird of New York.
The legislation had the unanimous support of the state senate, and on May 18, 1970, Governor Rockefeller of New York signed a bill declaring the eastern bluebird the state’s official bird. The gesture helped shine a national spotlight on the eastern bluebird’s plight as people around the country were filled with an urgency to restore the beloved bird’s dwindling population.
In 1982, the New York State Bluebird Society (NYSB) formed with the goal of educating New York citizens about the eastern bluebird while increasing the endangered bird’s population through a statewide nesting box program. The society urged New York residents to erect nesting boxes to replace those natural cavities lost to invasive sparrows.
Since the NYSB was established, thousands of nest boxes have been erected in New York and beyond, and a 2000 to 2005 bluebird survey showed that the bird’s population had increased by 70% as compared to a 1980 to 1985 survey. Today, the eastern bluebird's population is considered stable.
Building a bluebird home
While the eastern bluebird’s future looks promising, it could still use your help. If you are considering installing a bluebird box near you, here is some important information to know before you begin:
- Find a bluebird-friendly environment. Bluebirds favor open country with patchy vegetation. Meadows, fields, woodlands, farmlands, orchards and golf courses all make great homes for a bluebird nesting box. Refer to the Bluebird’s Society Nesting Box Guide to learn what nesting box is best for your region.
- Keep sparrows out. In some cases, nesting boxes may only serve to provide nesting opportunities for invasive species, such as house sparrows. If your nesting box has been taken over by a sparrow, you might consider removing the nest or blocking the entrance when the sparrow is away. Learn more about how to prevent house sparrows from invading your nesting box.
- Space out your nesting boxes. Bluebirds require up to 25 acres of territory, which they will defend from other bluebirds. Nesting boxes should therefore be kept at least 100 yards apart.
- Maintain your nesting box. Be sure to empty out old nesting material from the previous year in the spring. A bluebird might have multiple broods each year, so remember to clean out old nests as soon as a brood leaves so that the nest box can be used for a second or third nest attempt. Regularly monitor the nesting box for signs of rot or infestation.
Learn more about the eastern bluebird in our Field Guide.