Heard on repeat: Where are all the bluebirds this year?

"Where are all the bluebirds?"

It's a repeated observation this spring and early summer among birders, citizen-conservationists and others in Minnesota who anticipate the popular thrush's migration. Eastern bluebirds traditionally are one of the first songbirds to appear in late March and early April, a marker of another spring.

Their boxes should be a flurry of activity this time of year, with a first clutch of hatchlings already fledged and a second brood on their heels.

This year, however, is strikingly different. Where are all the bluebirds? Many that return to Minnesota spend winter in Texas, Oklahoma and Arkansas. Unseasonably severe winter cold in February through parts of the Central Plains and a swath of Southern states is believed to have killed untold numbers of bluebirds, some of which starved or froze to death. They were unable to rely on such familiar food sources as insects, spiders and berries that were covered by snow and ice in prolonged single-digit temperatures. There were reports from Kentucky and Arkansas, for example, of bluebirds found dead in nesting boxes, where they'd gather for safety from the elements. Nebraska, Iowa, Kansas, Missouri, Oklahoma and Arkansas had Februaries that ranked among their 10 coldest on record. Parts of central Texas suffered below-freezing temperatures as long as nine consecutive days from Feb. 10-19.

Volatile weather is a yearly threat to bluebirds and other species, but this year, observations all around Minnesota are of nesting sites as empty as they have been in years. The scene is the same to the east. The Bluebird Restoration Association of Wisconsin said online that it's fielded numerous questions about the birds' whereabouts and that "sightings have been few and far between."

The breeding population of eastern bluebirds is estimated about 22 million, with about 86 % spending some part of the year in the United States. And while historically, the songbird has recovered from devastating weather, their remarkable dearth this year and the specter of continued climate volatility have a resonance unlike recent years. Like so many species, theirs is a fragile existence, brought back from the brink in part by the goodwill and volunteer-caretaker work of groups such as the Bluebird Recovery Program [BBRP]. Minnesota's group, a nonprofit, includes people who build and distribute nest boxes and monitor them year after year — and for some, decades. It's there, on public and private land, that the bluebirds' absence this year is most felt.

"Certainly this is the worst year for bluebirds," said Bob Dunlap, a state zoologist with the Department of Natural Resources and a former president of the Minnesota Ornithologists' Union, who has observed birds in the state since the late 1990s. He said other species, such as eastern phoebes and hermit thrushes, also were affected by the severe winter burst and are noticeably fewer this year.

Populations fluctuate year to year, but Dunlap said he's seen fewer bluebirds during his Minnesota Biological Survey work focused on grassland birds. "It's been a noticeable lack for sure," he said.

Val Cunningham, who along with Jim Williams writes about avian life for the Star Tribune, said via e-mail that she has witnessed "a very slow year" on the bluebird trail on Como Park Golf Course she has watched for 17 years. Only two of 12 boxes are occupied by bluebirds. In other years, she might see five or six nesting pairs at this time of year. Cunningham said fewer tree swallows are nesting, which also is worrisome.

Ron Jensen, a BBRP coordinator in Hubbard County in northern Minnesota, monitors 75 bluebirds houses he's built and erected in and around Park Rapids. He has been at it for 15 years. Some bluebirds have been late to arrive and to nest, he said, while a few parents already have produced a second brood of eggs. Jensen said he is hoping to fledge 125 to 150 birds this season, or about half of his 2020 total.

Keith Radel, of Faribault, monitors more than 175 nest box sites over 50 miles in Rice County in southeastern Minnesota.

In 2020, Rice County reported 27 % of all the bluebirds reported to have fledged statewide by the BBRP. More than 3,800 bluebird young flew from their nests for the first time from 846 sites across the county. Statewide, 13,932 bluebirds fledged.

Radel said Rice County is seeing a down year, too. So far, anyway. Just three weeks ago, Radel said he was down 60 % from 2020, but like Jensen he's observed late-arriving bluebirds. That's given him hope. He expects some parents might yet produce a clutch, typically three to five eggs. "Either this is their first try, or they failed somewhere else," he added.

Radel, who has checked on and cared for bluebirds for 36 years, said their up-and-down cycle has been more persistent in recent years. The deadly weather isn't always elsewhere either. A cold, wet spring in 2013 limited crops — and insects — across southern Minnesota, and "[bluebirds] flat-out starved to death," Radel said. A little more than half the number of birds from 2012 fledged that year.

Regardless, Radel remained upbeat for a bit of good news to report several weeks from now. Plus, the number of chickadees that have filled the void and fledged (100 as of Monday on his trail) has been a bright spot.

"I am sticking with this," he said. "I am going to keep watching my trail as I have for years and keep helping [bluebirds] as best I can."

Dunlap acknowledged that bluebirds have the capacity to rebound. For example, less competition for nesting sites this summer could bode well for the birds that made it to Minnesota. Bluebirds can produce up to three broods each year.

Still, Dunlap said the expected frequency of unusual, volatile weather because of climate change is troublesome. There could be a threshold where bluebirds and other species, battered by repeated patterns of winter kills, don't bounce back as expected.

"That's my concern when we have this type of thing. Not necessarily just the year that we are in, but looking down the road. How many years of this does it take?" Dunlap asked.

One year sounds like too many for bluebird helpers hyper-attuned to their seasonal patterns. Mike Jeresek filed a report May 15 to BBRP about 35 sites in Houston and Fillmore counties. There were 15 empty, some of which until this year always have produced nesting bluebirds.

"Sounds like it is going to be a challenging year to be a bluebirder," he wrote.