When we think of birds of prey tackling hoofed mammals, we often imagine the golden eagle: that far-ranging embodiment of avian grace, power and lethality. Across their vast geography, golden eagles are known to occasionally tackle small (and typically young) ungulates: everything from pronghorn fawns and mountain-goat kids to reindeer calves and sika deer.

The similarly sized bald eagle, meanwhile, which overlaps with the golden across much of North America, is an equally majestic raptor most people consider a fish-eater and scavenger. Yet the national bird of the United States – the New World's representative of the "sea eagle" clan – is actually quite the versatile and opportunistic hunter.

And one surprised onlooker recently caught video evidence of this predatory flexibility – and an instance of a bald eagle taking a cue from a golden eagle's playbook.

Not long after sunrise on June 30, the Green Bay Press-Gazette reports, Julie Miller noticed a white-tailed deer fawn paddling along her stretch of shoreline on Lake Noquebay in northeastern Wisconsin. She pulled out her smartphone and began filming – mere moments before a bald eagle swooped out of the morning sky and tackled the fawn where it swam.

"I just felt so bad," she told the Press-Gazette. "Here I was enjoying the sight of that cute, little fawn swimming along, not knowing its life was about to end."

Her footage shows the eagle flapping a bit awkwardly in the shallows as it grapples with the submerged fawn, which Miller reports seemed to cease struggling after about 30 seconds.

The eagle eventually towed its prize to shore, took a breather for a few minutes, and then flew off. It was seen periodically circling overhead that day, and then alighted on the carcass in the evening to feed. Over the subsequent days, the bird repeatedly visited its kill, which by July 4 had been reduced (perhaps with the help of terrestrial scavengers) to hair scraps.

Later in the day the eagle took the fawn, Miller saw a doe in the area that "appeared to be searching", according to the Press-Gazette, and speculated it may have been the mother.

In 2009, researchers determined that a whitetail fawn they'd radio-collared on Michigan's Upper Peninsula had likely been preyed upon by a bald eagle. The fawn's final radio location pinged less than a half-mile from an active eagle aerie – shortly thereafter, its collar, two fawn legs and a scrap of hide were found in the nest alongside two eaglets.

Although that appears to be the only definitive published record of the phenomenon, Miller's sighting, she learned, came on the heels of one of her neighbours witnessing a bald eagle take a fawn just a few weeks before. Stanley Temple, a Beers-Bascom professor emeritus of the University of Wisconsin-Madison's Department of Forest and Wildlife Ecology, told the Press-Gazette it's possible the same eagle was involved, the raptor recognising a vulnerable prey item after its first kill. "The eagle [possibly] learned it wasn’t difficult to kill a fawn, so maybe it felt encouraged to do it again," Temple said.

Oregon-based field ornithologist Trent Bray, the Senior Field Trip Leader at Avitours, LLC, noted that bald eagles certainly live up to their reputations as eaters of carrion (everything from spawned-out salmon to roadkill) and "kleptoparasites" (often seen pirating fish from ospreys), even though they're capable predators as well. "Most active hunting I have witnessed with the generalist bald eagle has been opportunistic, usually coinciding in the winter months with large flocks of loafing waterfowl," he told me.

That said, Bray reckons that bald-eagle predation on fawns isn't quite so rare as the scarcity of direct observations suggests. "I imagine it occurs more frequently, but goes undocumented."

Bald eagles definitely consume their fair share of venison across much of North America, but the bulk of it surely comes in the form of carrion rather than ambushed fawns. This can cause trouble for them depending on the context: eagles risk lead poisoning when they dine on the gut piles left behind by deer-hunters, and when they dine on road-killed deer they risk becoming roadkill themselves.

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