Bird of the Month: Bluebirds
Fun Facts About Bluebirds
A member of the thrush family, bluebirds are found throughout North America.
All bluebirds are cavity nesters and will use an artificial nest box. Habitat and nest cavities had been disappearing for many years, but bluebirds have made an incredible come back due to thousands of bluebird nest boxes being installed across the country.
Eastern Bluebird numbers declined throughout the late 1800s and much of the twentieth century, suffering an almost 90% decline in population. Their numbers began to stabilized during the 1960’s and have slowly increased ever since. Among other reasons, competition for nesting space from the introduced House Sparrow and European Starling contributed to this century-long decline.
According to the statistics from the Breeding Bird Survey, survey-wide estimates of the Eastern Bluebird population show an increase of 2.4% per year for each year since 1966. The Audubon Society’s Christmas Bird Counts from 1980 to 2004 also show a three-fold increase in population.
Nesting occurs from March through August. Only the female incubates the 4-6 eggs which she maintains at a temperature of 98 to 100ºF.
Bluebirds are generally monogamous, staying together throughout the breeding season, and may breed together for more than one season. However, some birds may switch mates during a breeding season to raise a second brood.
Bluebirds may raise two and sometimes three broods per season. Pairs may build their second nests on top of the first nest, or they may nest in an entirely new site. The male continues to take care of the recently fledged young while the female begins to re-nest. Young of the first brood will occasionally help raise their siblings in the second brood.
Both sexes defend territories; however, the males tend to defend territory edges while the females primarily defend the nest site.
Males may carry nest material to the nest, but they do not participate in the actual building. They spend much time guarding their mates during this time to prevent them from mating with other males.
Families flock together until fall, when they merge with other family flocks. Some, but not all, bluebirds residing in the northern portions of the range migrate to southern latitudes, but those residing in southern latitudes tend to be residential.
Adult Bluebirds tend to return to the same breeding territory year after year, but only a small percentage (three to five percent) of young birds return to where they hatched.
Bluebirds love mealworms and can be drawn in with a small dish filled with mealworms.
Bluebirds are typically seen as a symbol for happiness. “Mr. Bluebird’s on my shoulder!”
It is likely that up to 70% of all Bluebirds die before reaching their first birthday. Most adult Bluebirds live for only a few years, while a small number live up to four or five years. The oldest recorded Eastern Bluebird was ten years old, with the oldest Western and Mountain Bluebird being recorded at approximately six years old.
A bluebird can spot caterpillars and insects in tall grass at the remarkable distance of over 50 yards.
Bluebird females of all species have duller plumage than males; this may reduce their visibility to predators.
Eastern Bluebirds will occasionally breed with Mountain Bluebirds and successfully raise young.
Bluebirds have no blue pigments in their feathers. Instead, each feather barb has a thin layer of cells that absorb all wavelengths of color except blue. Only the blue wavelength is reflected and scattered, resulting in their blue appearance to our eyes.
Unlike other Bluebirds, Mountain Bluebirds are able hover above the ground while searching for insects. This enables them to live in areas with few trees or shrubs, while Eastern and Western Bluebird need trees to provide the elevated perches from which they hunt.
Bluebirds rarely winter in areas where night-time temperatures routinely fall below 20º F.
Late winter and early spring cold fronts can be very dangerous for Bluebirds due to the depletion of natural fruit supplies and the lack of insects.
Bluebirds consume about 4 grams of food per day, or about 12% of their body weight. This is equivalent to a two hundred pound human eating 24 pounds of food each day.
Eastern and Western Bluebirds sit on an elevated perch while searching for insects; when one is spotted, they drop to the ground to capture it with their bill. This sit-and-wait technique is called drop-hunting.
Like many other birds, bluebirds make a high volume shriek when captured by predators. It is thought that these screams are used to attract other predators, which in turn will then distract the original predator long enough for the bluebird to escape.
As the days grow longer in the spring, a male bluebird’s brain releases hormones that stimulate the production of testosterone, which in turn stimulates the area of the brain responsible for singing behavior, thus triggering the male to begin its mating song.
Unpaired male bluebirds may sing up to 1,000 songs per hour, but average a more reasonable rate of four to five hundred songs per hour.
Bluebirds can fly at speeds up to 45 miles per hour if necessary.
Bluebirds raise their young in old or pre-existing nesting cavities and have a nesting success rate of about 60%. In contrast, birds that construct a new nesting cavity each year (such as woodpeckers) have a success rate of up to 85%. Predators are less likely to find a new nesting cavity than one that has been in existence for a few years.
Northern Flickers and Hairy, Downy, and Red-bellied Woodpeckers all produce nesting cavities suitable for later use by Bluebirds.
When choosing natural nesting cavities, studies have shown that Eastern Bluebirds select abandoned woodpecker nests at least 75% of the time.
The first Bluebird Nesting Box Trail was established in Adams County, Illinois in 1934, by T.E. Musselman.
Eastern Bluebirds actually appear duller after molting in the late summer than at any other time of the year. Their new body feathers have dull brownish tips that wear off during the winter, leaving them bright and colorful for the next breeding season.