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Dawn Chorus: Eagles on winter beach carrion [1]
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Date: 2025-03-16
November-December 2024
Salish Sea, Pacific Northwest
We generally think of Bald eagles as mighty predators, and they certainly are much of the time, but they also feed on carrion more often than you might think. Eagles are highly opportunistic in their diet, and will feed on whatever is most available and easiest to get. For example, while overall in North America Bald eagle diet is 56% fish, 28% birds, 14% mammals and 2% “other” according to Birds of the World, on the Colorado River in Arizona in winter they feed almost entirely on rainbow trout. In Yellowstone in winter, it’s 93% ungulate carrion while in summer there they feed more on birds than anything else. Even over small distances there are big differences, as for example here in Western Washington: on San Juan island eagles eat vast numbers of bunnies (introduced European rabbits) while on the nearby mainland they gorge on spawned out salmon for much of the winter. There are countless other examples demonstrating seasonal and geographic variation.
In western Washington State where I live, Bald eagles are abundant and I get good looks at a wide variety of their feeding behavior, from hunting and stealing to scavenging. Today I’m highlighting a particular scavenging incident I watched over a week last winter on a local beach.
The beach is a strip of cobbly gravelly bouldery sediment between steep rocky headlands on the southern margin of the San Juan islands. The adjacent land is privately owned, mostly by absentee owners, and with no road access and few visitors. In the winter tourist off-season that number goes down to almost zero, so wildlife doesn’t experience much human interference. My HOA owns (thankfully, since I’m too poor for waterfront property) a small parcel at the northern end of the beach where there’s a steep clay bank. The southern end of the beach is next to a wetland.
View from the HOA’s overlook, toward the north, on a rare sunny winter afternoon
I walk down to this bay as part of my daily constitutional, and watch for wildlife activity throughout the year. I see and hear eagles frequently.
November 27 , I saw an eagle down on the beach at the far end amidst the rocks and driftwood. There were a couple of ravens too though it was clear the eagle was discouraging them from getting close to what it was working on. I couldn’t really tell what it was. A second eagle was perched in a tree over on the headland.
Eagle with dirty face, and a raven
The other eagle (clean face)
Video from November 27:
I suspected whatever the carrion was, it had to be big since eagles just haul smaller carcasses off to feed on more privately. Larger carcasses must be eaten in situ. I figured I’d have a chance to watch the whole process from the overlook with each day’s visit.
November 28:
Given how the eagle had first started working on the carcass the day before, I was surprised not to see any scavengers on the beach there the next day. But there was one eagle perched on an islet out in the bay, for quite a while.
Bald eagle on a rock out in the bay
When I turned my attention to a cute little Pacific Wren on the clay bank, the eagle came swooping in to land at the same spot as the day before and start eating again.
Pacific wren foraging
Directly back to the carcass
This time enough of the carcass was visible so I could see it was a deer. Specifically, a spiker, ie a yearling male, by the unbranched antlers. What we have in the islands are Columbian black-tailed deer (Odocoileus hemionus columbianus), a Western coastal subspecies of mule deer. Deer are extremely overpopulated in the islands, a consequence of the settlers exterminating by 1900 all their natural predators, primarily cougars and wolves. These days deer mortality is mostly from car collisions and periodic disease epidemics. There is a hunting season but our deer are smaller than average and sometimes sickly so most hunters choose to use their tags elsewhere.
However farmers and gardeners have been known to take matters into their own hands since deer are voracious browsers and there’s limited forage for their dense population. Decades ago I invested in an 6-8 foot deer fence around my property, that being the only way to have a vegetable garden. People who have dogs say that helps.
How did this deer end up on the beach? Deer swim readily between islands but it’s unlikely to have drowned since they are strong swimmers (there was a crazy incident a couple years ago when a deer crossed paths with an orca, who luckily didn’t seem interested in it!). Sometimes deer feed on washed-up seaweed (I see tracks on sandy beaches) but this beach has poor footing and worse access. It’s possible a loose dog chased it off a cliff (that does happen). It’s also possible an unauthorized hunter dumped it in the ocean and the carcass washed up here.
Whatever its origin, this particular young deer became food for scavengers.
Sometimes the eagle lost his balance while yanking on the fur. He’d flare his wings to maintain position.
November 29:
Still working on the carcass, now pulling out guts as well as muscle.
November 30:
There were no eagles on the beach this day so I considered walking over to the carcass for a closer look. However the tide was high and after trying to navigate the hazardous footing between the driftwood and the clay bank, I gave up. But this view shows the stairs and the overlook where I watch the bay.
High tide, driftwood, eroding bank
Were three days enough to use up the carcass? Eagles can eat a large quantity and store that food in their crop to be digested over several days, so that might have accounted for their absence.
December 1:
The male eagle was back. A lot of the deer insides were now easily visible, ie. bone, muscle, etc. Eagles stand on a carcass for leverage, tearing through the tough skin where they can with their beak. It takes skill and patience (with no hands or artificial tools).
December 2:
This day I arrived just after the female eagle had finished feeding. She is bigger than him, which is how I could distinguish them. Likely on the other days I’d missed her feeding session. I was only there for about 20-30 minutes each day. But you can see all the white bird poop on the driftwood and rocks which tells us the birds were there much longer.
She is feeding while he watches and waits
Before she takes off for the trees
Video from December 2:
December 3, 4 and 5 there were no eagles on the beach when I was there. On December 6 there was one near the carcass but it wasn’t feeding, and flew over to the headland. By this point the carcass looked like there wasn’t much edible remaining.
Eagle is done.
The tide was low enough this time so I could walk down to take a look, and indeed there was nothing left but bones and fur, between the driftwood and rocks where it had gotten wedged by a high tide. All the soft parts were gone.
What’s left after bird scavengers have eaten all they can use.
So I can conclude it took two eagles, and possibly some ravens, six days to turn a small deer into valuable winter calories for birds.
🦅
I’ve seen other carrion being scavenged on the beach. Here an immature eagle feeds on what’s left of a raccoon, also in winter.
Survival rate for eagles in their first year is about 50%. A dead raccoon was a welcome meal for this immature eagle.
In summer carcasses are rendered down much faster than these deer and raccoon examples. That’s because we have lots of Turkey vultures from April to October. Here are two summer examples from my local beaches.
A dead seal pup that washed ashore was consumed down to fur in two days by about a dozen vultures on this same beach. There were a couple of eagles around too but that time the carcass was right below the overlook, and eagles are less tolerant of human presence than vultures. I can get within 20 feet of vultures feeding.
Two foggy days in August 2018:
Eagle and vultures in a tree down the beach
You can tell this is a new seal pup by its size, about the same length as a vulture. About half the seal pups do not survive their first year.
Seal fur/skin and flippers
May 2023:
A lot of birds were scavenging fish remains on a beach right next to a road, possibly left after some fisherman cleaned their salmon. There was nothing left but bones after one day.
The eagles ate what they wanted and left the rest for the vultures, ravens and crows
So, eagles have more competition for carrion in summer than in winter. The young spiker black-tail was a welcome boon for the local eagles in December. And lucky for them it was a calm week.
December 6. We don’t get many days this calm, especially in this particular bay. Prevailing winter storms blow this direction, onto the beach.
A week after the eagles abandoned the remains of the deer carcass, we had a storm and a high King tide. Waves washed right up through the driftwood onto the bank. When the tide went out, the driftwood was completely rearranged and the rest of the deer carcass was gone. Washed out to sea. Marine scavengers would take over from there.
December 13
The local sharp-eyed eagles jumped on a mid-winter food opportunity, turning an unfortunate young spiker’s death into eagle life. The deer’s nutrients did not go to waste. That’s nature.
The Dawn Chorus is now open for your birdy reports of the week.
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