As Minnesota bird lovers prepare to join thousands of others across the country in the Audubon Society's 109th annual Christmas Bird Count, the society is reporting that its year-to-year counts have detected a trend: birds moving north because of a warming climate.

A new Audubon analysis of counts from decades past shows that 208 of 305 species across the nation have moved north by about 40 miles, or about a mile a year, over the past 40 years. Gregory Butcher, Audubon's national director of bird conservation, outlined those findings for the Minnesota Audubon chapter at a recent meeting.

"Birds are the most mobile of creatures, so they do respond to global warming,'' Butcher said. "Birds with stable and increasing populations are moving north like crazy.''

By spring, Audubon -- a conservation group dedicated to protecting birds and their habitats -- plans to release a map showing state-by-state changes in bird populations. The counts indicate that 85 percent of forest birds, 84 percent of feeder birds, 75 percent of land birds, 59 percent of wetland-water birds and 46 percent of grassland birds have been steadily moving north, Butcher said.

In Minnesota, birds moving north include the tundra swan, the gadwall, the merganser, the bald eagle, the red-headed woodpecker, the cardinal and Cooper's hawk.

"The cardinal is showing up more and more in areas of northern Minnesota where it hadn't frequented before,'' said Ron Windingstad, an Audubon coordinator who has personally witnessed the change.

Some birds in decline

The Minnesota counts also have shown declines in some bird populations -- for example, that the number of red-headed woodpeckers is down 89 percent in the state over the past 40 years, largely because of habitat reduction, said Mark Peterson, executive director of Audubon Minnesota.

Bird populations naturally vary from year to year, so no one year is a fair reflection, and that is why the ongoing annual counts are so valuable, he said. "Since this is the only comprehensive statewide annual bird census, this is the primary tool we have for assessing what is happening to our bird population numbers,'' Peterson said.

"Birds are an early warning system that something is wrong in the environment when we see their populations decreasing,'' Peterson said. "Over time, by tracking these annual numbers, we can tell what populations are faring better and which ones are faring worse.''

Birds in trouble can point to possible sources of problems such as invasive plants, invasive birds, pollution or habitat alterations that are endangering birds, Peterson said.

The next count

This year's bird count will take place from Dec. 14 through Jan. 5. In the metro area, counting day is Dec. 20. By braving the cold to join the effort, people can enjoy the beauty of nature and "help scientists understand how birds are faring amid unprecedented environmental challenges,'' Audubon says.

The first bird counts were conducted on Christmas Day in 1900, organized by an early Audubon officer, Frank Chapman, as an alternative to killing birds in traditional holiday hunts.

Now the count is the longest running wildlife census in the country. Volunteers last year counted nearly 60 million birds across the North American continent.

In Minnesota, about 1,000 volunteers bearing binoculars and check lists fan out in 70 counting circles, each covering a diameter of 15 miles. At the end of the day, each counting team turns in tallies to its circle organizer, who totals them and files the findings on the Audubon website. The counts go into Audubon's database.

"This is a grand tradition in Minnesota,'' said Charlie Greenman, of Minnetonka, who with his wife, Bonnie Mulligan, and friend Richard Sandve, of south Minneapolis, have counted for 20 years. Their territory includes Lake Minnetonka, where they use binoculars and a sighting scope to count geese and ducks.

"One year we ran into a flock of white-winged crossbills, which is a wonderful bird more commonly seen in the northern part of the state," Greenman said. "They have crossbills for eating pinecone seeds."

Often a rare bird does appear.

"Last year in our counting circle there were several sightings of a bird called Townsend's solitaire," said Howard Tole, a biochemistry professor at the University of Minnesota who leads a counting circle centered along Hwy. 100 and covering parts of Minneapolis and the western suburbs.

Townsend's solitaire is a robin-size bird typically found in western Colorado, usually in the Rocky Mountains and pine trees, Tole said. "We had five in our counting circle -- the highest count anyplace in the United States,'' he said.

Tole's circle typically logs 50 to 60 species and 4,000 to 5,000 birds. Similar numbers come from all the other circles in Minnesota.

All can participate

Audubon welcomes all levels of bird watchers to the count, Peterson said. "Anyone is welcome to come. It's like Birding 101 with no tuition costs." Newcomers are paired with veterans in all circles, but volunteers are asked to bring their own binoculars.

Some people count in the metro area and sign up for three or four others in rural Minnesota, Tole said. "It's kind of fun to do counts in the rural area -- I enjoy that more myself -- because the birds are more unusual.''

Counting methods vary by their location, said Carl Greiner, a lab scientist for the Mayo Clinic who is the statewide coordinator of the Christmas Bird Count. In Minneapolis, St. Paul and Bloomington, "It's driving around looking for birds at feeders,'' he said. In northern Minnesota near Beltrami, volunteers ski for miles to make their counts and then camp overnight in a cabin in rough wilderness, Greiner said.

Carver Park Reserve is looking for volunteers for morning and afternoon counting shifts in the park on Dec. 20, said naturalist Judy Englund. The data collection is serious but there is a social camaraderie between participants, she said.

In years past, as many as 100 people have joined the park count. Two years ago participants were thrilled to see a golden eagle, a bird usually sighted much farther west, Englund said.

Laurie Blake • 612-673-1711