Bald eagle, goshawk populations going in opposite directions
The nearly half-century tally of birds that fly over Hawk Ridge every autumn is really a snapshot of annual migration, impacted by weather and natural cycles, and not necessarily a population survey. But the tale of two raptors that fly over Dulu...
The nearly half-century tally of birds that fly over Hawk Ridge every autumn is really a snapshot of annual migration, impacted by weather and natural cycles, and not necessarily a population survey.
But the tale of two raptors that fly over Duluth on their way south each autumn are shining examples of what researchers are seeing across North America - two birds heading the same way this time of year way but going in opposite directions as a species.
As of Thursday more than 1,200 bald eagles had been counted over Hawk Ridge, ahead of even last year's record pace.
Only eight northern goshawks had flown over.
Recovery beyond expectations
Bald eagles have recovered beyond anyone's expectations in recent decades after their numbers were decimated by DDT pesticide contamination and decades of wanton killing.
A few decades on the endangered species list, the outlawing of DDT and a lot of notoriety did wonders for bald eagles, and Hawk Ridge tells the tale. In 1973 counters saw just 23 eagles. By 1984 more than 100 eagles were seen at the ridge. The count topped 1,000 for the first time in the fall of 1993 and then just kept going up, hitting records of 5,778 in 2011, then 5,925 in 2016 and a new record of 6,099 last fall.
"We're getting more eagles in a day than we used to see in an entire season,'' said John Richardson, the head fall counter at Hawk Ridge.
"I wouldn't be surprised if we broke the record again this year considering where we are already,'' said Clinton Nienhaus, director of education for Hawk Ridge. Even in what has been a slow fall for raptor migration, eagles are 300 ahead of last year's record pace.
And it's not just a regional phenomenon. There were as few as 487 nesting pairs of eagles remaining in the entire lower 48 states in 1963. When the birds were removed from the Endangered Species list in 2007 there were nearly 10,000 nesting pair. This year the U.S. Fish and Wildlife Service estimate hit more than 15,000 nesting pair of eagles in the lower 48 states, with Minnesota having the highest number.
Bald eagles, true omnivores that will eat on already dead meat as well as hunt, appear to be taking advantage of things like road-kill deer cracases and open water winter fisheries near powerpoints to build their numbers even in northern areas, with some staying north all year. They also appear to be far more willing to tolerate each other than previously believed, with nests now spaced much closer together. It's unclear how high their numbers might go.
There are now an estimated 150,000 eagles in the U.S, half in Alaska and half in the lower 48 states, the U.S. Fish and Wildlife Service reports.
"We used to say they didn't like nesting within 2 miles of each other. Then we said 1 mile. Now, especially in good habitat, we're seeing them nest a quarter-mile apart,'' said Margaret Rheude of the U.S. Fish and Wildlife Service. "And we're seeing them nest in places that make you think. what the heck are they doing there? Like in a single row of trees between Minnesota corn fields. It's remarkable, really."
Birds of concern
Another species of raptor flying over Hawk Ridge this fall hasn't fared as well. Northern goshawks, a small hawk that thrives in dense, old-growth northern forests, are declining as fast as eagles are soaring.
In 1972, Hawk Ridge counters tallied 4,963 northern goshawks. Because the hawk's population is cyclical, following similar cycles of their prey like snowshoe hares and ruffed grouse, their numbers vary widely. By 1978 Hawk Ridge saw only 93 goshawks. But their numbers jumped back to 3,535 in 1982 at the top of another cycle.
Lately, however even the peaks of the goshawk cycles aren't going very high. In 1992 the peak hit only 2,040, less than half of 1972. By 2001 - the next peak - the count was halved again to 1,207. By 2012, what should have been a peak year, only 269 goshawks were seen. Last year saw a blip up to 327.
Most of the Hawk Ridge goshawks probably come from Canada and Alaska. But Minnesota goshawks appear to be troubled, too.
"There's something causing a very large trend across a very big area of the northern U.S. and Canada and Alaska. It's either an issue with prey or habitat... or both. Or maybe climate change might be a factor,'' said Gaea Crozier, nongame wildlife specialist for the Minnesota DNR. "In Minnesota, we don't know what the population trend is. We don't have that data. We do know that it's quite low, with a few birds spread across a big area. And we do know it's very susceptible to forest management. We're not seeing breeding or reproductive numbers we should be seeing. And that's across the Great Lakes."
The Minnesota DNR lists the goshawk as a "species of special concern,'' saying goshawks are dependent on large areas of older forest now lacking in the state. The DNR says Minnesota's northern forests have experienced a 50 percent decline in the number of large, connected tracts of old forest since the 1930s. That decline is expected to continue, both in Minnesota and farther north, as demand for older trees continues.
"They really like old aspen and old pine forest, and those are projected to keep declining because they are highly sought trees'' by the wood products industry, Crozier said.