A female osprey nesting on an island off the coast of Maine has had some sleepless nights lately.

The devoted mother's name is Rachel, and her family stars in a live webcam managed by the Hog Island Audubon Camp and hosted by Explore.org. The cause of her after-hours woes? The cause of many creatures' after-hours woes: a great horned owl.

This is the fifth year Rachel and her mate, Steve, have nested on Hog Island, and their brood has suffered some brazen predatory assaults before. In 2015 a bald eagle successively plucked both of the pair's young chicks from the nest while the parents were away fishing. And last year, later in the nesting season, an eagle nabbed a chick with one taloned foot while being hotly pursued by one of the adult ospreys; to escape the attacker, another chick decided it was as good a time as any to launch its inaugural flight. 

This time around, the troubles at the Hog Island osprey nest have come post-nightfall. In the past couple of weeks, a great horned owl has managed to abscond with two of the three chicks in Rachel and Steve's clutch. The owl paid its first murderous visit in the wee hours of July 11; it returned the next night for another nestling. 

Though not the biggest North American raptor, the great horned owl – the Western Hemisphere's eagle-owl – may well be the all-around fiercest. Nicknamed the "winged tiger" (or "tiger owl"), the bird is the very opposite of a picky eater: in a prey spectrum that runs size-wise from bugs to small foxes, horned owls will eat such varied meat as catfish, Canada geese and striped skunks. 

The owl's dinnertime fly-bys at Rachel and Steve's nest surprised observers only because the "winged tigers" aren't all that commonly observed on Hog Island. "We don't hear our great horned owls hooting out here often," Steve Kress of the Audubon Society told Andrew Del-Colle in an Audubon blog post about the predation. "In fact, I haven't heard any hooting this year. And we don't know of any active nests."

But otherwise the owl raids aren't unusual. Great horned owls readily hunt other raptors – including such formidable quarry as red-tailed hawks and snowy owls – and they've been known to kill adult ospreys. With their nearly noiseless flight and keen night vision, they often target the nests of other birds; they'll boldly strike at roosted parents, including great blue herons and even bald eagles, when trying for nestlings. The phrase "sitting ducks" comes to mind, though nest guardians (when they're present) are often able to thwart the nocturnal feathered stealth bombers. (Speaking of ducks…

Nest cams elsewhere have also caught horned-owl predation at osprey nests in action this season, including one at Belwood Lake in Ontario: the night of July 9, an owl killed one chick and (rather eerily) hung out awhile in the nest with the survivor, which it ended up preying on a couple of nights later. (Heads up: probably don't watch these if you're squeamish.)

At this point (and, FYI, you can really go down a YouTube rabbit hole of nest-cam owl attacks if you're into that sort of thing) you may be condemning the great horned owl as the bad guy here. Like orcas doing their thing or (non-winged) tigers doing their thing, though, it's really only a magnificent apex predator performing its essential ecological role. And nestling ospreys (like those of any other bird) face steep odds in the survival department even without marauding owls.

The brighter news from the Hog Island nest is that Rachel appears to have stepped up her guard duties: likely the same horned owl that preyed on the first two chicks returned the night of July 21 and actually got its talons into the surviving osprey nestling, but Rachel managed to drive the attacker away – not once but several times. 

In a follow-up Audubon blogpost by Del-Colle about this third owl strike, Steve Kress said, "What is surprising here is that Rachel seems to be learning new ways to defend her remaining chick ... [She] is changing her behavior by perching lower and closer to her chick, it appears she is learning from her experience and adapting her behavior to be a more successful parent."

You can follow the continuing saga – and find out whether Rachel's new anti-owl mettle sees her sole remaining chick through to fledging – over at the Hog Island webcam.

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