Question:
I help out the dolphin education program at the Spit. Across the river at Kiawah’s most eastward point of beach I often see a huge flock of birds. They seem to randomly all lift off and fly a short, low course for just a minute or two and then land back where they started. In air they remain closely packed just as they are on the ground. I have several questions:
-do we know what birds they are? They may be migrating but they are there for at least several days, I recall they are there all the time.
-is there an “alpha” bird who decides when to take off and when to land?
-If lift off is caused by a perceived threat why does that threat disappear so fast, allowing the flock to land in just a few minutes?
-how do the birds fly so very close to each other without collisions? I think the answer, if known, applies to schools of fish.
Thanks for your thoughts
Andy Allen
Answer: What great questions! To answer them, we asked two of the leaders of our Seabrook Island Shorebird program, Mark Andrews and Bob Mercer, to give us their thoughts, based on the above description and known behavior of our shorebirds.
Mark’s response:
Black Skimmers, terns, gulls all roost at the inlet and fly in large flocks. We’ve had
Semipalmated Plovers, Sanderlings, etc., but only in flocks of 50-150. Dunlin often fly in flocks like Red Knots, and are often imbedded in Red Knot flocks as well.
The flocks often fly when Bald Eagles, Peregrine Falcons and even Osprey fly over. Peregrine Falcons and Merlins are the main threat for smaller birds, and Osprey eat fish. Other unknowable factors can make a flock “nervous”. Just before takeoff you’ll often see widely separated individuals raise and lower their wings.
Bob had this response:
I would assume that the birds he is seeing are gulls, terns, and Black Skimmers.
A human visual reaction is about 194/1000 of a second, or 194 milliseconds – fast! Birds are faster! For a bird to react takes 67 milliseconds, or about 1/3 of the time it takes us to react. As the flock starts to move, the reaction time drops to 15 milliseconds. The hypothesis is that the first bird gets spooked somehow. We know from personal experience this may not be the result of a predator or other obvious stimuli. Animals do have personalities, with some being more skittish. Once a bird reacts, the 6 or 7 birds next it pick up the signal and start to react within 67 milliseconds. The 6 or 7 birds near each of them then jump into action. At that super-fast reaction speed, it does not take long for the movement to spread to the whole flock. While the birds in the flock pay close attention to the 6 or 7 birds in their immediate vicinity, they can also see how the birds farther away behave. This may enable them to prepare to react, which allows them to reach the super-fast reaction speed of just 15 milliseconds. As a flock of birds like shorebirds or starlings swoop around in the large “coordinated” flocks, the laws of mathematics and physics drive the eventual flock movement. No “leader’ is needed.
These details came from a website: How does a flock of birds wheel and swoop in unison? – The Straight Dope
Recently, I was able to take a few photos of the flock resting at the inlet in the afternoon. The birds most prevalent that day were Black Skimmers and Royal Terns. They started out on the Kiawah side of the inlet, but due to beach walkers who got a little too close, they soon took flight and landed on our side, giving me a closer look at the birds in the group. The birds did exactly what Andy said, periodically taking flight, circling a few times, then settling back down in the same or nearby location. Two Osprey were circling overhead, and a couple of dolphins were swimming in the inlet as well. The majority of the birds in the flock by far were Black Skimmers, who incidentally are white on the underneath. My observation, when in flight, the birds are flying in different directions, flashing different sides of their bodies, therefore seeming like a mix of white and black birds from a distance, when in actuality they’re mostly skimmers. At least that was the case the day I was there. Here’s a short video clip from that afternoon to illustrate my point.
We have a wide variety of shorebirds on our beaches year round, with many more stopping off to rest and refuel during migration. Opportunities to learn more about our shorebirds, and to volunteer as a Shorebird Steward, will be coming our way early in the new year. Consider volunteering as a steward, it’s a rewarding and educational opportunity with great benefits to our beaches and birds alike.
Submitted by Gina Sanders