Bald Eagles are common in the Salish Sea but right now they are abundant. On our last boat excursion out to the Rocks, just a few miles away, I counted 19 different eagles. Plus one more back at shore when we tied up. Eagle season!
We visit the Rocks regularly to see what’s going on with the wildlife out at sea. They are remote and protected from people so the variations in species we see are due to changing dynamics through the seasons (and from year to year). Populations come and go, rise and fall. Compared to my reports since early fall (Aug, Sept, Dec), there have been some big changes. For one thing the hundreds of cormorants that had packed the Rocks are gone and almost all the gulls too. Now the sea lions are sharing these barren rocks only with eagles. Mostly the eagles perch quietly gazing out to sea.
The Daily Bucket is a regular feature of the Backyard Science group. It is a place to note any observations you have made of the world around you. Rain, sun, wind...insects, birds, flowers...meteorites, rocks...seasonal changes...all are worthy additions to the bucket. Please let us know what is going on around you in a comment. Include, as close as is comfortable for you, where you are located. Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.
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Why so many eagles at this time of year?
The Pacific Northwest has one of the highest concentrations of Bald Eagles in the United States. We have over 150 nesting pairs in the San Juan Islands alone. Most head over to mainland Washington and British Columbia rivers during the fall to feast on spawned out salmon, and that’s the only time of year I won’t see at least one every day. But along with the residents back now for the breeding season now we also have three times that many who have migrated to spend January and February here — "snowbirds” who have left the frozen lakes and rivers of Canada, Alaska and Montana to hunt in our waters.
What are they eating? Lots of birds according to research reports (see Washington Department of Fish & Wildlife document at the above link). While in summer eagles here eat mostly fish, rabbits and carrion, in winter their diet shifts to more waterbirds than fish. No wonder the cormorants and gulls are scarce at offshore rocks now! Both resident and migratory eagles are especially attracted to waterfowl, many of whom have also come here for the winter from the frozen north, like ducks, mergansers, loons and grebes. Based on what I could see on the water this day the eagles were likely scanning for scoters, harlequins, murres, guillemots, auklets and herons. Or any of the scattered cormorants and gulls.
Another big change at the Rocks on this trip was among the sea lions. For the first time ever, I saw a Steller sea lion pup! It’s the small one directly below the eagle in the photo below (the eagle is further off and showed no interest in the sea lions at all).
While Steller Sea Lions have been wintering here forever, it was only big adult males as recently as 4 years ago. Gradually I’ve been seeing more females and youngsters joining them. Observers at Race Rocks near Vancouver Island recorded the first female and pup there in 2011. This pup appears to be nursing still. Unlike Harbor Seal pups who are independent a month or two after they are born, Steller Sea lion pups aren’t weaned for a year, or even two.
Below the motionless young Bald Eagles, young sea lions of different ages are playing. The sea lions depart for their rookeries in April and May to breed but evidently some females and youngsters are dispersing over the winter too.
These are Eastern Steller sea lions, whose population has gradually been increasing since the Marine Mammal Protection Act in 1972 prohibited hunting. Their status is in extreme contrast to the Western Steller Sea lions, a genetically distinct population found from Alaska to Russia, which has crashed in the past half century and is now listed Endangered. Scientists attribute their dwindling numbers to the precipitous decline in herring and other fish in northern waters. Those herring have taken huge hits recently, from petroleum poisoning to overfishing, and now the oceanic changes of global warming. The smaller Eastern population feeds opportunistically on whatever food happens to be present at the time, sharing those diminishing local resources with marine birds and other mammals in our area.
Winter migrant waterfowl spread out into every habitat here in winter: ponds, wetlands, shallow bays and open water. Since the biggest increase in eagles is offshore I have to assume they’re hunting diving ducks, alcids, cormorants and gulls. Scoters dive for clams and crabs along the bottom at 50-100 feet.
It’s a puzzle why there aren’t more eagles going after the abundant waterfowl in shallower waters, like Buffleheads. Could the resident eagles be driving them away from nesting territories?
The biggest congregation of eagles on this trip was near a favorite Scoter hunting ground, on a treeless headland of an uninhabited island. I counted eight Bald eagles here, but well-spaced.
As the WDFW report describes,
Bald eagles use their keen eyesight to search for food. In winter, when prey are concentrated, they look for other eagles in the act of feeding. Large congregations of eagles often occur where food is abundant. These gatherings are not at all friendly, resembling a group of thieves concentrating on stealing or beating out a neighbor to the food. The opportunity for an individual to eat depends on its aggressiveness, which may be influenced by hunger, size, and age. (p.8)
Mostly the eagles were perched quietly like this (which is why I was able to get an accurate count). One young eagle lifted off as we watched, passing us on its way to challenge an adult eagle.
Incoming birds with wings fully extended are usually able to displace a perched bird. Still, it was surprising to see a full-grown adult give way.
Another small island on our route is a major gull and cormorant nesting colony in summer. It’s empty right now. A pair of eagles flew in to survey it from the sign.
Bald Eagles mate for life, barring catastrophe, and raise new eaglets every year. If this pair is local, rather than visiting from the north, they may be surveying the spot, anticipating easy meals when summer comes. They’d know this island will have hundreds of gulls and chicks then, based on their past experience. And the migratory eagles will be gone by then.
~~o0o~~
As alway, all nature observations are welcome in the comments below. Tell us what you’re seeing in your own natural neighborhood.
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