Although home construction has been slow in much of Minnesota, one scenic sector is booming this spring: aeries in the Twin Cities.
Bald eagles added seven nests along the Mississippi River since last year, a 25 percent increase, continuing the rebound of the once-endangered national emblem.
The seven riparian aeries brought to 35 the number of active nests between Dayton and Hastings, according to a helicopter count this month.
"This is a big jump. Normally, we see two or three more a year," said John Moriarty, a Ramsey County Parks natural resources manager who does the counting. Noting that eagle pairs average two chicks a year, he added, "That increase means a lot more potential birds."
The eagle count, begun in 2006, is sponsored by the National Park Service and the Minnesota Pollution Control Agency. Park Service workers will return to some of the nests in May to obtain samples of blood and feathers from eaglets to test for toxins found in the fish they eat, said Bill Route, a Park Service ecologist who manages the project.
Bald eagle numbers have risen as the river has become cleaner and produced more fish, since the federal Clean Water Act was passed in 1972. The birds seem to have adapted to human activity; they even have nested near a runway of the Minneapolis-St. Paul International Airport and on an island upstream from the Interstate 694 bridge in Fridley.
The number of eagle nests in the Twin Cities metro area along the Mississippi River has risen from about 10 in the mid-1990s to the current 35, plus additional nests around metro-area lakes, Moriarty said. Eagle nests are considered successful if they produce at least one offspring a year.
"The eagles are reproducing very well," said Route, the park service ecologist. He noted that nests along the Mississippi often have three chicks, and occasionally four, in good fishing areas.
A Park Service study found that the 72-mile stretch along the Mississippi through the Twin Cities, called the Mississippi National River and Recreation Area, had the most young per nest among three areas studied from 2006 to 2008. The average was 1.9 eaglets per nest, compared with about 1.5 per nest for the St. Croix National Scenic Riverway and 1.2 for the Apostle Islands of Wisconsin in Lake Superior. During the three-year period, seven dead eaglets were found, including a pair that drowned when their nest fell into a lake and another killed by a bacterial disease.
The eagle feathers are tested for lead and mercury; the blood samples for the pesticide DDT, PCBs and other toxic industrial chemicals absorbed by fish. "We have no data to suggest the [eagle] population has problems because of these contaminants," Route said. He added, however, "we don't know about sub-lethal effects."
Climbers go up
Next month professional climbers will scale some of the nest trees to remove eaglets, sometimes with their parents screeching nearby. The young, which can't yet fly, are carried in pouches to the ground for sampling and then returned to their nests.
"We let them go on the ground and they stand there looking at us," Route said. "Little eaglets are used to sitting on nests 3 or 4 feet wide. They are programmed to sit in that spot. They don't go running around."
Sometimes the larger eaglets peck or claw their captors. "Their beaks are pretty wicked and their talons are worse. They are strong enough to stick a talon into your arm and they don't let go,'' Route said. "We are very careful."
Many of the majestic birds migrate elsewhere, flying as far north as Manitoba and south to Arkansas. They take several years to mature and then mate for life. An interesting change this year was finding two new nests relatively close to others in the area between Cottage Grove and Rosemount, Moriarty said. The area now has about 10 nests, the most concentrated section in the Mississippi survey.
"We used to think eagles had large territories and wouldn't nest within one or two miles of each other," Moriarty said. But this area "has a series of nests less than half a mile apart. That's closer than we have seen them since they rebounded."
Bald eagle numbers plummeted across the country to a low of 417 nesting pairs in the lower 48 states in 1963. That was partly because of the toxic pesticide DDT, banned in 1972, that leeched into waterways and then into fish the birds ate, according to the U.S. Fish and Wildlife Service. Eagles were listed as a federal endangered species in 1967 and "delisted" in 2007, when Minnesota had an estimated 2,300 pairs, said the state Department of Natural Resources. Bald eagles are still protected by the federal Bald and Golden Eagle Protection Act.
Two of the new nests found this month were on islands near Anoka and Dayton, bringing to six the number north of the I-694 bridge.
Jeff Weaver, who lives by the river in Anoka, recently saw a pair of eagles cavorting. "They were doing some amazing acrobatics. Rolling and diving and squawking. It's a treat to watch."
Jim Adams • 612-673-7658