Eastern bluebirds are a symbol of summer happiness and likely one of Minnesotans’ most beloved birds, up there with chickadees and loons. When enjoying a spring or summer day on our hobby farm, I can’t help but pause to take in this small thrush’s sweet, warbling song and brilliant colors. They have been cheerful company on many days of garden, horse and chicken chores.
A Recovery Success Story
While eastern bluebirds are currently common due to the proliferation of nest boxes and bluebird trails, that hasn’t always been the case. They declined dramatically from the 1930s to the 1960s due to loss of habitat and nest site competition from house sparrows and European starlings, two non-native birds and bluebird enemies. Together, partners like the DNR Nongame Wildlife Program and Bluebird Recovery Program sponsored workshops, published education materials and promoted bluebird houses. Restoration efforts paid off. Minnesota now has one of the most successful bluebird recovery projects in the nation.
Not Really Blue
Eastern bluebirds have big, rounded heads, large eyes, plump bodies, and alert posture. Their wings are long, tail and legs fairly short, and bill short and straight. Males are a vivid, deep blue above and rusty or brick-red on the throat and breast. Females are grayish above with bluish wings and tail, and a subdued orange-brown breast. And guess what? They aren’t really blue, but gray. Their feathers bend light so they look blue. When light enters their feathers, it bounces off tiny air pockets and cells so that only the blue wavelengths reach our eyes.
Bluebirds prefer habitat of mixed hardwood forest and grassland with short, sparse, mowed or grazed vegetation. Perches such as scattered trees, powerlines or fences are important. They inhabit open woodlands, meadows, old fields, roadsides, pastures, hay lands, prairies, orchards, golf courses, backyards or city parks of every county in Minnesota.
Bugs and Berries
Bluebirds are ground foragers, primarily catching insects caught on the ground much of the year. Major prey include caterpillars, beetles crickets, grasshoppers, and spiders. They typically hunt by sitting alertly in the open on a perch and scanning the ground. They drop to the ground after insects with fluttering wings, followed by a quick return to the perch. Occasionally, they catch insects in midair. They can sight their tiny prey from 60 feet or more away. In fall and winter, bluebirds eat large amounts of fruit such mistletoe, sumac, blueberries, dogwood berries, hackberries, and juniper berries.
Bluebird language is diverse. Their song is a fairly low-pitched warble of several phrases. Typically, unpaired males sing this song from a high perch or sometimes in flight to attract a mate. Their most common call is a soft, short, low-pitched tu-a-wee with a querulous tone. Bluebirds use it in all seasons to stay in touch or signal to nestlings that food is on its way. When bluebirds get too close to each other, they let out a single, harsh screech. If nervous at the approach of a ground predator, a loud, continual chit-chit-chit is uttered. And when attacking predators or other intruders, bluebirds may dive-bomb them and clack their bills.
Some bluebirds winter in Minnesota, but most migrate south, returning in March. They nest April to July, typically raising two broods. They depend on cavities excavated by other wildlife, such as woodpeckers, or nest boxes. The male fights feistily over and defend about five acre territories. He displays at his nest cavity to attract a female, bringing nest material to the hole, going in and out, and waving his wings while perched above it. The female builds the nest by loosely weaving together grasses or pine needles, lining it with fine grasses and occasionally horse hair or feathers. The eggs, usually five to six, are pale blue, or rarely white, and incubated 13-16 days by the female. After a nestling period of 18-19 days, the young take flight. Bluebirds typically live two-three years, five if lucky. The oldest recorded eastern bluebird was over 10 years old. Birds of prey, snakes, and various mammals, especially cats and raccoons, are their main predators.
Keeping Bluebirds Common
How can you help ensure this cheerful bird remains common?
- Keep open habitats healthy. Encourage a diversity of native grasses, forbs and fruit-bearing shrubs that will provide insects and fruit, and periodic disturbance such as haying, mowing, grazing or prescribed burning. This management will also benefit monarchs and pollinators such as bees.
- Keep cats indoors or on a leash, as noted in the 2015 February-March Creature Feature.
- Reduce or eliminate use of chemicals that may negatively affect bluebirds and their food.
- Buy or build nest boxes carefully designed with entry holes and dimensions that meet bluebird needs. See the Peterson plan in Woodworking for Wildlife for a tried and true design. This useful book is available from Minnesota’s Bookstore on line.
- Properly place and maintain nest boxes.
- Choose locations in open habitat with short vegetation, with nearby perching sites, at least 300 feet from brush, and on high ground.
- Call 811 before sinking posts to have the site checked for underground utilities. Use predator guards to eliminate climbing predators or ½ inch metal electrical conduit over ½ inch rebar. Entrance holes should be five to six feet above the ground and face east or northeast.
- Do not overload an area with nest boxes. Space them at least 100 yards apart.
Allow nest box use by native birds such as chickadees and tree swallows. To accommodate tree swallows that are competing with bluebirds, pair two nest boxes about 20 feet apart.
- Avoid placing boxes where house sparrows are abundant. Remove house sparrow nests and eggs.
- Avoid brushy areas where house wrens are likely to reside. They poke holes in other birds’ eggs, carry out nestlings and take over nest boxes by filling them with sticks.
- Check nest boxes at least once a week during the nesting season until nestlings are 12 days old to identify and address problems such as blowfly infestations or house sparrow nests. After that, monitor only from a distance to prevent chicks from jumping or flying prematurely. Remove old nests as soon as the brood has flown.
- Establish and maintain a bluebird trail of five or more nest boxes where they can be easily checked.
- Consider recording nesting data with NestWatch, a nationwide monitoring program to track status and trends in the reproductive biology of birds.
- Join the Bluebird Recovery Program. Founded 1979, it was the first state bluebird organization in the nation. Enjoy its next annual Bluebird Expo on April 16 in Byron.
- Learn even more from the North American Bluebird Society.