The Eastern bluebird, indigenous to North and Central America, is said to have once been as common as the American robin. A population decline starting in the early twentieth century reduced the number of Eastern bluebirds by an estimated 90 percent, inspiring a grassroots movement to save them. Key to the movement’s success was the Peterson bluebird nest box, designed by Dick and Vi Peterson of Brooklyn Center.
Eastern bluebirds (Sialia sialis) have a long history in North America, with mitochondrial DNA research suggesting the birds evolved into a distinct species about 2.5 million years ago. Fossil evidence dates the birds’ presence in the upper Midwest at 8,000 to 10,000 years ago, around the end of the last glacial period. The stories of many Native American cultures recognize bluebirds as symbols of spring and bearers of hope, friendship, and happiness. Minnesota Ojibwe called (and still call) the bluebird ozhaawashko-bineshiinh (blue bird). The corresponding word in the Dakota language is ziŋtkatȟo.
Eastern bluebirds are secondary cavity nesters, meaning they build their nests in previously hollowed-out spaces. Although they require a sheltered nook for nesting, bluebirds can’t drill cavities with their beaks. In nature, they nest in other birds’ abandoned roosts, hollow rock niches, wooden fencepost notches, and dead or dying trees.
As American settlement expanded during the nineteenth and twentieth centuries, those natural nesting options dwindled. Logging removed woodlands, and metal fenceposts replaced wooden ones. Pesticides and insecticides killed the birds and the insects they fed on. Most devastating was the incursion of two European cavity nesters: the house sparrow (English sparrow) and the common starling (European starling). These non-native species invaded bluebird nests, killing off adult birds and their fledglings.
By the 1960s, the nation’s Eastern bluebirds faced extinction, and a decade later the birds were on the National Audubon Society’s list of “vanishing species.” Bird lovers throughout the United States searched for ways to reestablish the bluebird population, recognizing that recovery would require human intervention.
Minnesotans Dick and Vi Peterson joined the search, focusing their efforts on finding a substitute for nesting cavities. They lined “bluebird trails” with nearly 500 nest boxes, checking weekly during nesting season to identify elements that would keep the chicks warm, dry, and safe from pests.
Every component of the Peterson nest box focused on protecting the birds. A wide roof provided shade on a hot summer day and shelter from wind, rain, and snow in inclement weather. The steep slant of the roof prevented raccoons and house cats from snatching the babies inside. The wedge shape of the box made it easier for fledglings to leave the nest when they were ready. An entry hole, measured to the sixteenth of an inch, was sized to keep starlings out.
The Petersons shared their nest-box pattern with individuals and conservation groups at no charge and led workshops teaching the construction process. Children built the boxes in 4H clubs, Girl Scouts, Boy Scouts, and Camp Fire Girls. Junior and senior high school students constructed Peterson boxes in shop class or as Future Farmers of America. Civic groups established bluebird trails in parks and on golf courses, at cemeteries, and along country roads. Volunteers took notes, recording when a nest was built; what kind of bird built it; when eggs were laid; and how many chicks hatched.
The Peterson nest box worked. Although a 1979 spot check of Minnesota bluebirds revealed just eleven pairs, a bird census three years later showed a count of 1,490 fledglings. In 1992, 14,800 fledglings were counted in Minnesota, more than any other state in the nation. Nationally, researchers reported that Eastern bluebirds showed a preference for Peterson boxes when they were given a choice of nesting sites.
Dick Peterson, described as a “tinkerer,” built and tested more than 5,000 nest boxes between 1978 and 1998. A retired Northwest airline pilot, David Ahlgren, simplified Peterson’s design and developed a method for constructing an entire nest box from just one board. He then spent twenty-five years cutting out more than 85,000 nest boxes and selling them to birders around the world or donating them to schools and non-profit groups.
Over time, the efforts of countless volunteers stabilized Minnesota’s bluebird population, with bird census reports averaging just over ten thousand fledglings a year. In 2025, the Bluebird Recovery Program of Minnesota dropped “recovery” from its name, noting that the bluebird population has recovered.