When two Great Horned Owls started nesting outside Nevada’s Desert Research Institute in early March, the staff there were thrilled. They quickly contacted the state’s Department of Wildlife, and together the organizations set up a webcam so that they—and the rest of the world—could check in on the owls when they weren’t in the office.
That’s when things started getting weird.
The owls, as it turned out, weren’t a mated pair like DRI and NDOW staff originally thought. They were two females, nesting side by side, and they had what appeared to be the same male mate. Great Horned Owl males are responsible for bringing all food to the nest in the early stages of egg and chick rearing, and the webcam showed the male coming to visit and feeding both females each night.
The females’ comraderie didn’t stop there, however. When the larger of the two female’s eggs failed to hatch, she hopped across the rock that separated the two nests and started helping the smaller owl care for her eggs. When the eggs hatched, the larger female stuck around, helping the smaller feed the chicks. One chick has since left the nest, but the other remains, and the second mom still swings by to help out.
This behavior has never before been seen in Great Horned Owls, says David Catalano, supervising wildlife biologist for NDOW. “I’ve been trying to find literature on it,” he says. “And there’s just nothing. There’s nothing on this.”
There are other cases of birds—male and female—feeding nestlings that aren’t their own. The practice is called alloparenting, or cooperative breeding, and it can be beneficial for all involved.
“Sometimes alloparents are siblings of the nestling, or aunts or uncles,” Christina Riehl, assistant professor at Princeton who studies cooperative breeding in birds, said in an email. “When the alloparent is related to the young, they share common genes, so the alloparent is helping to raise its genetic relatives (just like a grandparent or an uncle taking care of their younger family members).”
For example, Greater Anis, members of the cuckoo family, build large nests that they share with up to four breeding pairs, a group setup that helps the anis compete for choice nesting spots. The adults work together to incubate the eggs and raise the chicks, with female anis caring for their own young and the young of other females. Sociable Weavers build massive nests composed of many small “apartments” for mated pairs, and often, after the offspring fledge, they stick around and help their parents feed their younger siblings.
But when birds engage in alloparenting of offspring that aren’t related to them and without any evolutionary benefit, it’s known as misdirected parenting, and it can be harmful for the birds’ own eggs or chicks. It can happen among birds of the same species or birds of different species, and it isn’t unheard of among owls: Barn Owl fledglings, for instance, have been known to abandon their own nests and move to nearby nests, where they’re fed by parents that aren’t their own. Young Barn Owls typically engage in nest-switching if they’re having trouble finding food on their own after fledging, or if they aren’t getting enough food from their own parents.
That misdirected parenting is probably what’s going on with the Great Horned Owls, Riehl thinks. After incubating her eggs, the larger female owl was ready to take care of her own chicks. When they failed to hatch, her maternal instincts drove her to care for the offspring of her neighbor.
One chick has left the nest, but one remains. While the real mom is almost always present, the second mom still stops by to help out.
“Adult birds have a strong behavioral response to nestlings, especially if they're trying to raise their own young,” she said. “The presence of nestling owls—their begging calls, their appearance, and their movements—might have stimulated the second female to bring them food, even though they're not her own nestlings.”
The novelty of the situation—added to the fact that nest cams tend to be tremendously popular—has garnered the owls plenty of attention. Catalano says an average 200-320 people are watching the cam at any given time, and the intrigue of the co-parenting moms has created a lot of interest in the community.
“We’ve had a few university professors, retired and active, that have been asking questions about it,” he says. “We have a great deal of citizen scientists that have taken it upon themselves to research these owls and their behavior. The community has really come together to figure out why these birds are doing this.”
As for what exactly is going on with this family dynamic, no one knows for sure. Luckily, even if the impetus behind this unusual trio isn’t totally clear, the setup seems to be working out for them; they share feeding responsibilities, and the one chicks has already fledged. It’s a peaceful, if unconventional, little family—at least, most of the time.
“In the evenings, when the father’s bringing food, [the females] do battle,” Catalano says. “But nobody ever gets hurt—it’s more, ‘hey, these are my kids, chill out.’”
Still, while the family appears happy enough, parenting chicks that may not be related to her isn’t benefiting the smaller owl in an evolutionary sense.
“Hopefully next year she'll have her own nestlings to raise,” Riehl says.
Correction: This article originally misstated which owl's eggs didn't hatch. It was the older, larger owl that unsuccessfully nested and began helping the other mother owl.
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