This is the time of year you see flocks of birds heading south. If they are geese, they typically fly in a skein or V formation. Ducks fly in looser skeins, and smaller birds like shorebirds and songbirds fly basically in a bunch. Pelicans and cormorants fly in a line. And many blackbirds and starlings fly in enormous flocks.
Let’s look at geese. There are no leaders, birds just take their turns up front. The large wing of geese produce updrafts or vortices at the tip. So each bird flying just behind the wingtip of the one in front gains lift from those vortices. The lead goose gets no advantage, so it lets a substitute take over after a while. The wings of ducks and other smaller birds don’t produce these vortices, so they just fly in a loose flock. Pelicans and cormorants will fly in a line over water as they get lift from the surface of the water, but if they fly higher they often form a V.
To me, one of the most amazing feats of bird flight is the gathering of thousands or even hundreds of thousands of birds flying as if they were a coordinated flock. Look at one of the YouTube videos of Red-winged Blackbirds wintering in the dismal swamp of Virginia.
.jpg){kind=link}
It appears to our eyes that the birds are turning and swooping on cue, gracefully in tune with each other. But high speed photography reveals that they are not all that graceful, turning at slightly different times and sometimes colliding with each other. That they can do this at all is because they are not in a round, spherical flock. Their flock is shaped like a thick pizza, only 5-7 birds thick.
Watch how the flock moves, like pizza dough being thrown into the air. Why that shape? Because the birds can only keep track of 6-7 birds around them. Any more birds and there would be more collisions. Think about yourself moving in a crowd of holiday shoppers. How many folks around you can you keep track of? Maybe 5-7. Watch those flocks this winter and notice the pizza shape. Amazing.
Coming from the old English “floc”, flock, meaning bird groups, has been around for 600 years.