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A few eastern bluebirds attempt to stay for winter in Minnesota, but nearly all of them spend the cold months in states south of us. They return in the greatest numbers between the middle of this month and mid-April.

Last year, two eastern bluebird migrants arrived March 3 in the backyard of Ray and Marlene Simon on the edge of Northfield, Minn. A week later, six very skittish bluebirds were spotted at Frontenac State Park. The first migrants were on time, but a colder and snowier April delayed nesting.

Keith Radel of Faribault reported that the first baby eastern bluebird hatched out May 18 — 17 days later than 2017. Radel maintains a bluebird trail containing 175 pairs of nesting boxes covering about 50 miles, all in Rice County not too far from his home. Hundreds of young bluebirds fledge from his nesting boxes each year.

Numerous individuals and organizations have helped bluebirds make a remarkable comeback in the last 40 years by establishing and maintaining trails of nesting boxes. The annual Bluebird Expo highlights that work. This year's gathering is April 6 at Cannon Falls High School, beginning at 9 a.m. All are welcome. Check the Bluebird Recovery Program of Minnesota website (bbrp.org) for more information.

Eastern bluebird habitat includes farmlands, orchards, roadsides and open woodlands. They nest in natural tree cavities, old woodpecker holes, wooden fence posts, and the nest boxes we put up for them. Insects are the main part of their diet, but they also eat fruits and seeds during the months when insects are scarce.

A female eastern bluebird is a fainter version of the male. He has a sky-blue head, back and tail, a rusty-red throat and breast, and white belly. Their sweet song is made up of three or four soft, gurgling notes. This 7-inch bird is a favorite of many people, but 50 to 75 years ago it nearly was eliminated in Minnesota because of the increased use of insecticides, the dwindling number of wooden fenceposts, and the competition for nest sites from two introduced species, the house sparrow and the European starling.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.