Sunday, February 12 was a wild and windy night in Pittsburgh, Pennsylvania. Fifty-five mile-per-hour winds whipped through the region, ripping down signs and knocking out electricity for some 6,000 residents. But what was a temporary inconvenience for people bordered on the catastrophic for a pair of Bald Eagles nesting on a hillside in the Hays neighborhood.
At 9:33 p.m., the mother eagle was hunkered down in the nest, incubating the pair’s lone egg laid just two days prior. We know this because the Audubon Society of Western Pennsylvania and a company called PixController have a live video feed trained on the tree 24 hours a day during nesting season. The eagles have also inspired an army of loyal viewers, people who tune in every day from as far away as Greece to watch the eagles and chat about their days. (Audubon recently profiled the group in this story: “The Bald Eagle Nest Cam That Hatched a Global Community”)
But at precisely 9:34 p.m. that night, cam-watchers were witness not to nest-building or grooming, but a disaster instead. The hackberry tree these eagles have called home for the last four breeding seasons swayed back and forth violently as the winds kicked up. Then: a series of loud cracks, a flutter of wings, an enormous crash, and . . . darkness.
Fortunately, both adult eagles were able to survive the incident. As for the lone egg, well, let’s just say eggs are poorly equipped to save themselves from falling out of the sky.
While it may seem like a stroke of bad luck for this particular tree to come crashing down, it’s really not all that unusual in the world of eagles.
“Bald Eagle nests can grow to be 2,000 pounds because the birds work on them year after year,” says Rachel Handel, communications director for the Audubon Society of Western Pennsylvania. “The nest simply becomes so heavy that a tree can no longer support it.”
Now, what’s particularly interesting about the Hays pair is that unlike most Bald Eagles, we have eyes on them at almost all times. Within 10 minutes of the nest-tree falling, some cam-watchers were reportedly already down at the nearby trail to check on Mom and Dad Hays, as the eagles are known in Pittsburgh. Thanks to these dedicated followers, we know that within hours of losing their home, the eagles started collecting sticks for the reconstruction project. And within days, they’d set up shop in another tree about 200 yards away.
This was all more or less to be expected, according to Robert Mulvihill, an ornithologist at the National Aviary in Pittsburgh. Bald Eagles are known to re-nest in a single season following a calamity, but given how large and intense these structures are, it usually takes a bit of time. And that’s okay, Mulvihill says, because the female typically needs around 29 days to come back into egg-laying condition. Her body has to reset, so to speak.
But this is where things get kooky. Not only did the eagles whip up a new nest in under a week—an impressive feat, but again, not an entirely unprecedented one—but by Sunday, February 19, the pair were already showing signs of incubation. That’s just a week after the nest fell.
While the new nest is visible on the webcam, it is too far away to be able to see if there’s truly an egg, and Handel says they won’t try to move the camera until the fall, so as not to disturb the birds. But students of Bald Eagle behavior have other ways of knowing an egg is likely present.
For one, the eagles are taking turns holding a vigil in the nest for full 24-hour cycles. There’s really no other reason to do that if there’s no egg. And two, Handel and others have observed the birds leaning forward as they stand up in the nest. This is usually an indicator that they’re rolling an egg around to keep it incubated evenly.
So, what’s going on here? The best we can tell, Mulvihill says, is that the female was able to stay in her current reproductive state all while she and her mate built a new nest. If this is what took place, then the egg in the nest right now isn’t actually the first egg of a new clutch, but likely the third egg of the clutch that began in the doomed nest.
Bald Eagles stagger their egg-laying by two to four days, which means Mom Hays would have just been getting ready to lay another egg as the nest tree came down. Without a serviceable incubation spot, she then probably laid that second egg on the ground somewhere as the pair rapidly rebuilt a new home. Amazingly, the construction was finished in time for number three.
Two eggs is a typical clutch size for Bald Eagles, but this pair raised three chicks to fledging just last year. Mulvihill says it’s even possible for eagles to lay four eggs in a season, though this would be extremely rare. How many eggs each pair lays is probably a mixture of the female birds’ genetics as well as an indicator of how much food is in an area and how skilled the eagles are at acquiring it.
Bald Eagles are long-lived animals, living up to around 30 years in the wild. And Mulvihill says that monogamy helps pairs get better and more efficient at breeding each year over that lifetime. In fact, losing a nest now and again can even be a good thing, since nest-building helps reinforce the pair-bond.
But for all we know about eagle nesting behavior, Mulvihill suspects this sort of rapid re-nesting and resumption of egg-laying is never-before-seen behavior. And several experts on Bald Eagle biology that he has contacted agree—so far as anyone can tell, there’s no precedent for this in the scientific literature.
While it seems the webcam community will have to settle for one chick as opposed to three this year, the whole saga is a reminder that there’s no time for grieving in nature. Furthermore, tragedy for the first two eggs may actually benefit the remaining sibling.
You see, staggered egg-laying leads to staggered hatching. This usually means the last egg to hatch must fight for its scraps or wait until its older siblings are full before eating. The third egg in a clutch, then, is less likely to survive than the first or second. But due to recent events, the current egg has effectively been pushed to the front of the line.
“That egg might have been a runt in the other nest, but now it’ll be the big one,” Mulvihill says. “Its chances of surviving just went up.”