Over 3,000 bald eagles were counted recently on the Upper Mississippi River National Wildlife and Fish Refuge. - Photo by Helen Anderson

Assistant Manager, Tony Batya, scans the treetops for bald eagles. - FWS photo by Cindy Samples

Tony Batya, Assistant Manager scans the treetops for bald eagles. - FWS photo

Migrating Eagles Gather on the Mississippi

On a chilly March day, nearly 50 staff and volunteers of the Upper Mississippi River National Wildlife and Fish Refuge and other partners counted 3,165 bald eagles on the Refuge. “We’re trying to capture the peak of migration on the Refuge and with numbers like these it looks like we were successful,” said Lisa Reid, biologist on the Winona District of the Refuge.  This count was conducted for the first time last year when more than 2,700 eagles were recorded.

On March 19, twenty-three crews of 1-3 people canvassed the Mississippi River from boats and cars, each following established routes along the 261-mile long refuge.  The main channel had just opened up about a week earlier, but many of the backwater areas were still frozen.  The boat crews accessed areas that could not be observed from the road, while the car crews drove the length of the refuge on both sides.

“It’s great to get out on the water and see all of the wildlife returning” said Refuge Biologist Eric Nelson as he, Reid, and volunteer Todd Paddock, motored into a  backwater near Winona, Minn., in time to spot five eagles sitting on the ice.

The eagles were temporarily concentrated on the refuge, waiting for signals to push them northward to the breeding grounds in Minnesota, Wisconsin, Michigan and Canada. In the coming weeks, increased day length and gusty south winds would push the majority of eagles out of the area.

During the count, each eagle was tallied along with the time, location, and the bird’s age (i.e. mature - full white head and tail; or immature - brown or mottled head and tail).  Both years about two-thirds of all eagles counted were adults.

The high proportion of adults at this point in time matches the theory that adults migrate sooner than younger birds. Adults are eager to arrive early on the breeding grounds where they compete for nest sites and mates. Conversely, immature eagles have their biological limits and therefore, no apparent interest in early arrival, so they meander northward.

So, how do surveyors keep from counting a particular eagle more than once?  Though all duplicate eagle sightings can’t be eliminated, they are minimized in a number of ways.  The first is to limit the time that the surveys are completed.  The count is conducted refuge-wide on one day with a push to finish in the morning. 

The second relies on crews to pay attention where eagles are moving as they are counting.  And finally, back in the office, eagle sightings are reviewed for potential duplication. This year 130 sightings were dropped from the count because birds were counted in areas of overlap by car and boat crews. These safeguards only minimize duplicate sightings, but there are also birds that never get counted because crews can’t access ice-covered backwaters.

Though most eagles observed throughout the day were migrating northward, some were “resident” eagles that had already begun nesting. With that in mind, crews also checked eagle nests, old and new, for signs of nesting activity, such as an adult incubating or pairs perched “on territory” next to the nest.

Three new nests were found in the Winona area alone.  Last year there were 165 active nests on the refuge; 20 years ago there were only 12 active nests.  New nests are found each year, some a result of pairs replacing destroyed or abandoned nests, and others the result of an increasing eagle population.  The recovery of the endangered bald eagle is clearly evident on the refuge.

Another spring count will be conducted nest year to get an idea of the average use of the river at this time of year.  After that, the refuge will take a break from the count for about five years and then start the cycle over again.   Documenting eagle use of the refuge now will enable future managers to determine trends through time.