Date: 3/14/19 8:14 am
From: <phawk254...> [arlingtonbirds] <arlingtonbirds-noreply...>
Subject: [Arlington Birds] Seven Bald Eagles Reported Simultaneously at Mystic Lakes (possibly Ten)
For more than twenty years I have been following the return of Bald Eagles as a wintering bird and then a breeding bird once again in eastern Massachusetts, especially with regard to the Mystic Lakes. In the 1970s and 80s the best opportunities to see a Bald Eagle (usually an adult) were in March, when the increasingly warmer rays of sunshine and longer days caused ice to melt on ponds, lakes and rivers. Frequently one found winter kills of fish released from the possessive ice. This "manah from heaven" attracted hundreds of Herring and Ring-billed Gulls and provided a valuable food source for the few Bald Eagles wintering in the eastern U.S. migrating back north to attempt nesting. In years when you were lucky to see one Bald Eagle in eastern Massachusetts in a year, Great Meadows National Wildlife Refuge in Concord during March was one of the best places to find one (and a lot of gulls.) The gulls were always a good clue as to where the fish kills were, and when they all went aloft screaming, you knew to look up for an eagle.

I'm stating that because there were several extraordinary events in my experiences with eagles over the past two days. On Tuesday March 12 I saw 6 Bald Eagles concurrently on the lower lake. Three on the ice and three more soaring overhead, all on or close to the southern end of the lake.

On Wednesday, March 13, I saw and photographed 6 Bald Eagles on the ice concurrently, all immature. and saw one subadult/adult on the far shore, so I had seven Bald Eagle concurrently, the largest concurrent count at the lakes of which I am aware. One huge white-bellied immature female had captured a fairly large fish and actively began "mantling" it, spreading her wings out attempting to prevent any other eagle from seeing that she had prey, and hopefully deterrring them from trying to take it. It didn't work. It appeared that every Bald Eagle within the 781 area code had heard about her catch and came to share in her bounty. Five immatures, all but one white-bellied, frequently leapt into the air, spreading their wings, trying to intimidate her into dropping the fish. It looked like an Irish step dance competition. Ultimately, she flew to a tree with the prey, pursued by a smaller immature. She ended up flying off with it to the opposite shore and apparently dropping it when harassed.

While watching the six on the ice, I met Jack Kelly of Wakefield, MA. Jack was watching the eagles on the ice without benefit of binoculars or camera, and was beating himself up over it. He remarked to me that on the 12th at about the same time he had seen ten Bald Eagles on the ice together at the same time. He accurately counted the six today and assured me he had seen ten on Tuesday. He seemed credible in knowing what eagles look like, but on Tuesday there were immature Black-backed Gulls on the ice near the eagles. To the unaided eye they could look as big as one of the young male eagles. Ten eagles was clearly possible, but there were no photos to confirm the unaided vision report (and they were far out).

In analyzing my concurrent counts and photographs over the past several months, I had concluded over the past two weeks that we had had 8 distinctly different Bald Eagles on the lakes, clearly identified by photographs, and I believed there was ample evidence that the minimum total was at least ten. Based on the number of very white-bellied immatures seen today without any juveniles and only one apparent adult/subadult, I would conclude we have had at least 12 and likely more distinctive individuals on the lakes this past six weeks or so. I am still going through my photos, often shot at a considerable distance, and some spectacular closer shots generously sent me by some of the local photographers.

Wednesday was dominated by immature birds that were white-bellied, showing variable white everywhere (especially on the belly), with very limited dirty white on the head or tail. Technically, we are at the point where most of our eagles become one year older, so it can be a bit confusing. (I will have a separate post suggesting how to identify individual Bald Eagles and "age them" in the near future.) Two of the white-bellied birds yesterday were virtually as white bellied as a Redtail, though Redtails do not have a dark brown bib above the white belly. One was a small male so that at first seeing it in a not-too-distant tree, my first thought was Redtail!

The ice shelves present in the lower lake are melting quickly. They are handy for the eagles in that they can perch closer to the fish and waterfowl they are hunting, including jumping a short distance off the ice onto a fish. They can eat the prey out in the open on the ice, which exposes them to harassment by other hungry eagles. (Whenever an eagle catches prey and starts to eats it on the ice, most every other eagle in viewing distance tries to see what it can get from this encounter.) Eating on the ice helps them protect the prey and themselves perhaps better than attempting to carry the prey in flight to a wooded perch, which exposes them to harassment while flying. Even eagles often drop prey while pursuing evasive flight. Sated eagles often leave some of the prey remains on the ice for others including crows and ravens and gulls, to eat, and often eagles will return time and again, after they've had time to digest their meal, to see if anyone left ANYTHING they can eat.

As the ice disappears, so too will most winter-kill remains. The number of eagles on the lakes should diminish. Adult breeding birds are on territory and generally don't tolerate other eagles, especially adult-plumaged ones nearby. The immatures will hang out somewhere like teenagers on a Friday night, looking for something to do, socializing, hoping that somebody will have found food they can scarf. MK, the three-year old bird hatched on the Charles River, has tended to act like the Mystic Lakes are her 'hood. Will that continue over the spring and summer? Will she convince the small adult-like Bald Eagle, a presumed male, with whom she hung out for several weeks earlier in the year, that they make a good couple and should play house, preparing for a more serious relationship ahead? Will she act possessive about THE TREE and major perches around the lakes?

Without the ice, it will be much more difficult to see the birds, especially when perched in trees on the western shore. If you go to the dam to look, remember that eagles spend about 90-95% of their lives sitting and watching, looking for food. If they are not flying, the cryptically colored immatures can be very difficult to see even with binoculars. Waiting for some considerable time can be required, followed by a brief explosion of activity. Within minutes of having seven eagles in view at one time, none were visible.

One last note. MK, the three-year-old who has lost her white-belly and gained a yellow bill, has developed an apparent fixation on a Red-throated Loon who has been on the lower lake for almost a week. Twice she has been seen diving repeatedly on the loon trying to take it. The loon dives and swims farther underwater than the ducks or even the Great Cormorant she has chased or taken in the past. So far the loon, in basic plumage, has eluded her, but after doing so yesterday after a flurry of attacks, MK retreated to THE TREE, while the loon called out plaintively. I have no idea if it was an exclamation of frustration or of victory. The saga continues.


Best,

Paul



Paul M. Roberts
Medford, MA
<phawk254...>
 
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