I'm voting for Black Scoters as well. I frequently see very tight rafts and line formations off of Seawall Picnic Area in Acadia, albeit not as huge as Carol's. Here's one eBird list with a few photos (my estimate was 105 for that raft). Linear rafting is very common for this species in my experience.
Given that Black Scoters are late northbound migrants, perhaps this large flock could be a modest pile-up of northbound birds?
In addition to Carol's wondering about rafting up for protection against eagles, maybe this could also be a group courtship thing, getting everyone's hormones in sync for the breeding grounds and jostling for mates? Whatever the answer, this is a cool phenomenon. Thanks for sharing, Carol.
Craig K
On Mon, May 28, 2018 at 9:54 AM, Carol Muth <suzmuth@gmail.com> wrote:
Thank you for your responses to our seabird question. Halifax Island is about a mile offshore from here and the birds appeared to be about half to two-thirds of that distance from shore (closer to the island). We are used to seeing groups of DC Cormorants make daily flights back and forth, from sea toward mainland in morning and back again at evening. This did not resemble the usual DC Cormorant behavior and the birds seemed smaller, but it is possible. Common Eider also congregate here (not as many in recent years as in the past) but the usual groups are females with young and often they are near shore; we can hear their humming. Occasionally we see groups of Eider farther out but they don't seem to be doing the motivated directional movement that the birds showed yesterday. We see single to a few Black Scoters close to the rocks or much father offshore, but before this we have never noticed such a large group headed seaward together. But they seem to be the most logical possibility. Thanks for suggesting this.I wonder if the group movement of smaller birds is a defense against Eagles. Two days ago, at about 7 pm four Eagles were putting on a dramatic show close to shore. Two were adults, one had a faint buff band at the end of its white tail (an almost-adult?) and one was entirely black, no white visible on breast or anyplace else. After some dramatic swooping and chasing of the group of four, the young (?) black Eagle dove into the branches of a tall mature fir (or possibly spruce) near the water. It was facing toward the trunk of the tree about 10' off the ground, probably looking out at the other Eagles through the branches. At this point it was hard to tell the others apart. Two were strafing each other like dive-bombers, the chaser flying full-tilt into the midsection of the chased. Then there were numerous maneuvers on high with rapid descent, legs stretched full out and talons distended. Two birds would approach each other at full speed in this posture- yikes! Sometimes there was just chasing of the third bird. Half a dozen times or more an adult bird (I could not tell them apart when they were in action) would swoop into the conifer on the shore where the black (young?) Eagle was sitting. After a minute or two it would fly out again to rejoin the aerial activity but the black eagle remained. I think this might have been mating or dating or parent checking on the young? I had the binoculars in one hand and the bird-guide in the other, looking for info. The activity was fast and furious and non-stop for about half an hour, with only a few short breaks. Then a pair of the adults flew off to toward the small islands a mile away and I had to make dinner. When I looked again the young (?) Eagle was gone from the tree.On Mon, May 28, 2018 at 8:35 AM, Merle and Anne Archie <ravensreachme@gmail.com> wrote:Hello Carol, how far out where the birds? If I knew a distance estimate it may be possible to make an educated guess. If it was pretty far out the birds could be Double-crested Cormorants as their migratory flight pattern is very much what you describe. If it is a bit closer in the birds could be Black Scoters. They are the last sea ducks to move north in large numbers.
Brant were still being seen up on Grand Manan Island and it's kinda, a little, possible the birds are Brant but that would be my last resort for an answer!
Anne
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