Bald eagles are concentrating in huge numbers along open water on both the Fox and Wolf rivers in our area. Menasha's Jefferson Park recently boasted more than 80 eagles, creating an amazing sight along the edge of ice. / Rob Zimmer/For Wisconsinoutdoorfun.com
The morning of March 4 began just like many others this winter. A moderate snowfall gently tumbled from the gray clouds while the landscape was blanketed in white. Temperatures were hovering right around zero, with little to no wind.
This day that started just like any other was about to get very interesting.
Making the rounds of my usual owl watching hotspots, snowy owls began to build in numbers I haven’t seen in my lifetime. As you know, if you’ve been following my blog, Facebook page and Twitter account, I have been following the snowy owl irruption regularly. However on this day, I recorded double the number of birds normally spotted along my routes.
As their number soared well above the normal five or six owls I typically encounter (which, in itself is a spectacular, rare treat), I began to suspect something incredible was taking place.
At the same time, I received a tip that 50 bald eagles were concentrating at the mouth of the Fox River in Menasha. While I have posted from this location a few times over the last couple of weeks, noting one or two dozen eagles in the area, the thought of 50 aroused my curiosity. So, I left “my” owls and sped on over to Menasha.
As I approached the park, I began to count the eagles standing guard along the Fox River from downtown Menasha east to Lake Winnebago.
By the time I finished counting, I had tallied more than 80 magnificent bald eagles in this relatively small, concentrated area.
Abundant prey and open water
According to Tom Erdman, curator of the Richter Museum of Natural History at the University of Wisconsin Green Bay, the birds are likely congregating in such large numbers due to the availability of prey.
“Eagles get concentrated where there is open water and fish. Often, fish get stunned going through dams and spillways or whatever is set up for power generation. Easy picking,” Erdman said.
The age of the birds, as well as where they traditionally spend the winter also contributes to the high concentrations we are currently seeing.
“It takes 4-5 years for eagles to reach maturity to breed. So younger birds can just hang around. Adults in Wisconsin should be back near nest sites and working on nests. Adults that are wintering here from much further north, such as the Upper Peninsula of Michigan and Canada, will hang around a bit longer. You also have to remember we now have around 1,000-plus nesting pairs in the state, so eagles have become pretty common,” Erdman said.
Roosting in trees, as well as lined up along the ice at the edge of open water, the eagles were everywhere. One tree held nearly 30 birds, while other trees scattered on both shores held anywhere from 6 to 12 eagles.
Hundreds of ducks, such as goldeneyes, mergansers, redheads, mallard and others, rafted on the open water as far as the eye could reach. In addition, 1,000 gulls or more harassed both the ducks and the eagles for food. There were hundreds of Canada geese, as well as several swans, here as well, creating an ever-growing tide of spring migrants.
It was the eagles, however, that stole the show.
Literally dripping from the trees, these magnificent birds often swept into huge circles in the sky, leading one another on aerial chases around the expanding area of open water, then up and down the river at fearsome speeds.
Adults and young birds alike joined in the spectacular winged assaults. Occasionally the eagles would lift to the sky and swoop down among the flocks of ducks, creating an eruption of birds into the wintry sky.
As for the large number of snowy owls present in Outagamie County, Erdman again attributes this to abundant prey.
Since snowy owls are birds of the wide open countryside, they don’t require open water, but instead, abundant rodents and other prey.
“Owls are a different story and probably reflect very healthy populations of meadow voles, rats and some birds,” Erdman said.
“I’ve watched then hunt pigeons, not often successful. Gray partridge and pheasants work, too. I suspect you must have lots of voles.”
In addition to snowy owls and bald eagles, the Fox Valley is also seeing a large influx of red-tailed hawks in the area, along with a few rough-legged and red-shouldered hawks, and many residents are reporting Cooper’s hawks and sharp-shinned hawks stalking their backyard bird feeders.
— Rob Zimmer: 920-419-3734, email@example.com