Outside my office window in the afternoon, I see flocks of crows, robins and starlings heading for the roost. Lately it occurred to me that I'm able to identify them at a glance, not by looking at the individual birds but by looking at the shape of the flock. This skill was particularly useful at the robin roost on January 6 because it was too dark to see individual birds.
As you can see in the pictures above, the flock shapes can be different even in birds of the same size. From left to right are four flocks: American robins, European starlings, double-crested cormorants and tundra swans. (First two photos are by Tom Pawlesh, last two by Chuck Tague.)
Here are some flock shapes I can think of:
- American robins: loose flock, widely spaced. Each bird maintains the same relative position within the flock.
- Starlings and pigeons: tight flock, synchronicity. Every bird makes the same move at the same time.
- Double-crested cormorants: J-shaped flock or a long line. The flock looks scraggly.
- Geese and swans: V, J or crescent-shaped flock.
- American crows: A loose flock in which each bird has his own idea about where he wants to be. Individuals show considerable positional movement within the flock. The birds look like black rags flapping in the sky.
- Blue jays: A loose flock so widely spaced that they sometimes look like they're not traveling together. Individuals maintain the same relative position within the flock.
- Cedar waxwings and American goldfinches: The flock moves in unison but individual birds change position within the flock, mostly by moving up or down. American goldfinches say "potato chip" as they fly.
- Small finches, common redpolls: Fly fast in relatively tight flocks. The flock moves in unison. Individuals zip forward or slow down but maintain positional integrity.
- Cowbirds: have a cool hopscotch pattern as they sweep across a field searching for food. (comment from Chuck Tague)
- Brown pelicans: The flock travels in a long line, skimming the surface of the ocean. They will even skim the surface of high rise buildings at the beach. Each bird synchronizes wing movement with the flock: first bird flaps downward, then second bird, then third, then fourth...
- On water American coots huddle close together in an extremely dense flock in the presence of a bald eagle.
- Turkey vultures: Soaring birds. Each bird goes his own way but they stay together. They hate to flap.
- Cranes: Soaring birds who travel in flocks, sometimes in a loose V.
- Hawks and falcons: no flock at all.