This past weekend, Steve and Rachel, an Osprey couple residing on Audubon's Hog Island, lost a chick to a nighttime raid by a Great Horned Owl. Last year the pair saw two such raids, and the attack made the entire community following the family on Audubon and explore.org's nest cam anxious: Would the owl return as the one last year did? To deter the predator, Hog Island staffers set up artificial lights to keep the owl away and provide the visibility Rachel would need if it did return. (Ospreys have poor vision in the dark, and female Ospreys protect the nest during the night.) The lights did not work, however, and the owl returned last night, taking advantage of a rare moment when Rachel had left the nest to chase a Great Blue Heron. By the time she made it back, it was too late. The owl was already at the nest, and though she fought it off once, it eventually returned to take another chick. Video of the incident is above, but be warned that it can be disturbing for some.
These two attacks are just the most recent in a string of predations in the past few years on the Hog Island Osprey nest. While upsetting for the many followers who feel attached to the birds, the interactions captured by these cameras provide raw glimpses into the natural world. In response to last night's attack, Steve Kress, executive director of Audubon's Seabird Restoration Program and Audubon's vice president of bird conservation, sent a letter to the nest cam community sharing his thoughts on these attacks and what he, as a scientist, has learned from them. The letter, which has been lightly edited, can be read in full below.
I was saddened again by the news this morning about the second Osprey chick. Many years ago when I first saw Rachel sheltering her chicks at night, I thought it was about keeping them warm in the Maine night, but now I realize that there is clearly much more to this behavior. Now that we have the wonder of the camera and repeated owl and Osprey interaction, I am increasingly aware that the predation we have seen at Rachel and Steve’s nest has repeated itself over many generations. Nocturnal attentiveness by Rachel demonstrates to me how time and trial have led to the behaviors we see today. Guarding the chicks at night is not only about offering shelter from weather. She is protecting the chicks not only from weather but from inevitable predators. It is why she stays at the nest all night without leaving to feed herself, it is why she rests with at least one eye open, and it is why she has the behavior to quickly chase away any large bird near the nest. And it’s why Osprey Steve, the nimble protector, focuses on the vicinity away from the nest to chase off diurnal predators like eagles, providing food for Rachel and the chicks—so she can effectively cover the home front. And it’s likely even part of the reason why chicks have a mottled plumage that gives them camouflage against the nest. Seeing this long evolutionary past—leading to the behavior we see today—helps me understand that predation and protection from predation are ongoing dramas that are the backdrop against which individuals like Rachel learn and adjust their day to day behavior (like sitting closer or further from the chick to better offer protection). Owls and eagles have had much to do with shaping the way Ospreys look and behave.
Ospreys are also closely linked to humans—especially through their nest site selections. South of Maine along the Atlantic coast of the U.S., more than 90 percent of ospreys nest on artificial structures (learned this recently from Dr. B). This is because they nest on utility poles, navigational aids, and a wide assortment of artificial structures. In Maine that number is lower because many Ospreys continue to nest in trees. And wherever they nest in trees, they are vulnerable to owls. At Pond Island NWR in the mouth of the Kennebec River, where Project Puffin researchers are protecting more than a thousand pairs of Common and Roseate Terns, Great Horned Owls often raid this colony and the forested islands are more than a mile away.
Whether owls and eagles take Osprey chicks or not depends on chance and opportunity. The most recent attack might not have happened if a Great Blue Heron had not lured Rachel off her nest, giving the owl the opportunity to pounce. But clearly the risk at this nest is presently high and the odds of another occurrence are great. We will continue to attempt to deter predation at this nest, just as we would at any bird nest. And I encourage the Osprey community to keep the recent predations in context of past success at this nest. Over the previous six years (while we have enjoyed the Explore.org cams), Rachel and Steve have fledged 10 chicks from this nest. And more from the years before. This nest clearly has a productive history. The recent attacks from eagle and owls point to growing risk—but also to the increasing diversity of large predators on the Maine coast, a reflection of the health of the environment.