When Jim Thomas came into his office one morning in late February, he realized he was not alone. “I heard this racket outside my window,” says Thomas, a hydrologist at the Desert Research Institute in Reno, Nevada.

There, he witnessed a battle between ravens and a pair of great horned owls, two species that sometimes grapple for territory. The owl couple had decided to make a home in the rock-strewn ledge outside the window, and soon prevailed.

Staff members were delighted to have great horned owls so close. But then things took a strange turn: A third owl showed up, a female. (See five baby bird cams not to miss this spring.)

The two females began laying eggs, five in total, only about a foot apart. Meanwhile the male began providing them food, bringing back mice and the odd rabbit.

This highly unusual behavior is the first record of polygyny—a male mating with two or more females—in great horned owls, says Christian Artuso, an ornithologist with Bird Studies Canada.

For one, these birds of a feather decidedly do not flock together; they're territorial and usually don't nest near one another. Perhaps more importantly, they’re monogamous.

Polygyny has been recorded in related species, such as barn owls and Eurasian eagle owls, but is still very rare among raptors.

That may be because it requires bountiful prey, a situation in which the male can provide two females with enough mice while they are nesting, Artuso says.

David Catalano, an ornithologist with the Nevada Department of Wildlife, agrees. “Very, very odd,” he says.

Misdirected Parenting

The institute decided to set up a webcam to broadcast live footage, and the animals have become an Internet sensation. “It’s been quite frankly amazing,” Thomas says.

But then it got more weird. The larger female, the second to show up, did a poor job of tending her eggs, which failed to hatch, Catalano says. When the smaller bird’s eggs yielded two owlets, she began caring for them as well, sheltering them from elements and venturing out to fetch mice.

This could be a type of misdirected parenting, in which the larger owl saw the owlets nearby and thought they were her own, he adds.

It’s also possible that the smaller female is actually the larger one’s daughter, or perhaps they’re sisters. (See 13 pictures that capture the beauty of birds.)

That would help explain why the birds are more comfortable around each other than most great horned owls. But “without determining their genetics, everything is just a guess,” he says.

Though the females sometimes tussle—“they get into some pretty good battles, pecking at each other"—generally they get along. “To be honest, they’ve co-parented quite well."

Empty Nesters

As for the owlets, the show is almost over; one left the nest last week, jumping off the ledge of the building before safely landing below. Staff members report the owlet is being fed by its parents and doing fine. (Watch a mother owl take on a snake—and win.)

This is normal owlet behavior; after about six to eight weeks, the youngsters leave the nest and take up residence close by, such as in the low branches of a tree or bush, which serve as a launch platform for future flights, Catalano says.

The other owlet remains, but soon, it too will leave the nest. “It could be any day now,” Catalano says. And with that, the threesome will split up.