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Eagle numbers along river are down, but overall trend is up or stable

Eagle numbers along river are down, but overall trend is up or stable

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If you haven't seen as many bald eagles in the Quad-Cities this winter as some years, you are not alone.

Kelly McKay hasn't seen many either.

McKay is a wildlife biologist from Hampton, Illinois, who has been counting eagles for more than 20 years as part of the Bald Eagle Midwinter Survey conducted under the auspices of the U.S. Army Corps of Engineers. The goal is to collect, analyze and maintain long-term population data on eagles, a once-endangered species. The counts are conducted along rivers that have been traditional winter foraging habitat.

This January McKay counted only 698 eagles on his seven routes that include an 80.5-mile stretch along the Mississippi River from Clinton, Iowa, to Keithsburg, Illinois, and a one-mile stretch of the Rock River where it enters the Mississippi. Other people make counts along other river routes across the country.

McKay's highest count was 4,958 eagles in 2014, which was a record-breaking year.

But this year's lowish numbers do not mean bald eagles are in decline, according to Stephanie Shepherd, a biologist who analyzes statewide data for the Iowa Department of Natural Resources, and Jo Fessett, who compiles the numbers for the Illinois Audubon Society.

What the numbers do mean is that eagles weren't hanging out along the Mississippi River in big numbers in January, they said.

And even in McKay's lower numbers there was the good news that immature birds, or the eagles' replacement population, made up a healthy 34.2% of the birds he counted. Last year that number was down.

Shepherd said that state-wide, 2021 "was definitely a lower year."

All told, there were under 2,000 eagles counted state-wide, she said. "That's one of the lower counts in the last 10 years, but we are not concerned," she said.

Temperatures during the counting dates in January were relatively mild, "which leads to them being more spread out," she said.

The Iowa DNR uses two sets of data to gauge eagle health  — the midwinter survey along rivers and a nesting survey. "The results of both surveys suggest that the bald eagles that nest and/or winter in Iowa have stable or increasing numbers," Shepherd wrote in her 2020 status summary.

Fessett said the same is true in Illinois. "We know that, overall, eagles are increasing. We are seeing them everywhere, and the adult-to-juvenile ratio is running about 60-40.

Why the fluctuation, and what about their food? 

The midwinter count seems to fluctuate widely from year to year, and Shepherd said she is not sure why.

She doesn't see much correlation between the number of birds and the amount of ice on rivers or even overall temperatures.

"The availability of food is the most obvious root motivation for bald eagles to move across the landscape," she said, but the survey does not collect information on this.

Inland, eagles find road kill, deer and small pigs that died in hog operations.

The inland migration of eagles to eat this kind of food has been concerning to McKay for the past 10 years. Because he doesn't see many gizzard shad (a type of fish eagles eat) in lock chambers, he fears the fish's population is plummeting, thereby "forcing" eagles inland.

But Dave Bierman, team leader of the Iowa Department of Natural Resources Mississippi River Monitoring Station in Bellevue, Iowa, said that is not the case. His team sets out a variety of different sampling gear in all the different river habitats from June to the end of October, and the gizzard shad population "is right around average," he said.

Fessett said eagles are getting to be more acclimated to people and have less fear about coming into urban areas.

A friend in a residential Springfield subdivision saw an eagle eating a squirrel on her front yard. "You don't even see a red-tailed hawk do that," she said. 

A concern with eagles eating deer or other animals shot by hunters is lead poisoning, Fessett said.

For example, all birds brought to a rehab center in Decatur are tested for lead content, and all the eagles being brought in are testing positive, she said.

Eagles 'may be getting close to carrying capacity'

Overall, "despite the increasingly large fluctuations (in the midwinter survey), the overall trend since 1994 is upwards," Shepherd wrote.

"This upward trajectory is settling into a flatter trend in recent years, though, which is to be expected as eagles may be getting close to carrying capacity."

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