I watched the true meaning of "birds flocking" recently. It was a warm early December day, in the early afternoon. In a not-too-distant tree there were maybe 70 or so chattering starlings, a murmuration of starlings, as such a flock is called.
All of a sudden, as if on cue, the birds took to the air and flew in " tight formation," veering this way and that in perfect unison over the golf course across the road from our home. Soon they were joined by maybe 40 more starlings coming from a different direction, which merged with this first mass without incident. They melded seamlessly into one synchronized black cloud and continued the aerial dance.
The gist of this account is this type of "choreographed" flying is not for entertainment, but protection, and as I watched, I saw it was to confuse a predator. What I assumed was a Cooper's hawk was following at a safe distance and, at one point, dove toward them, only to come into view again empty-handed, or I should say empty-clawed? I can only imagine just how bewildered the hawk must have been, which is one of the reasons behind flocking. Sandpipers also flock tightly for this very reason.
Communal roosting is common among crows during non-breeding months, and flocks may be seen, all heading to the same direction to, or from, a roosting site, and as mentioned last week, so also do starlings, grackles, blackbirds and shorebirds. They, and other species may also gather into flocks to feed. Often, robins, bluebirds and cedar waxwings visit our crab apple during colder months.
Another form of flocking, known to most people who spend a lot of time outdoors, doesn't adhere to the synchronous movement mentioned above, but is a form of protection, actual or perceived. Most notably termed mobbing, it occurs when a loose flock of crows, sometimes called a "murder of crows," harass an owl, hawk or other predator. I have often found barred owls by following the excited "cawing" of a number of crows.
In another encounter with this behavior while kayaking the Housatonic River, I watched crows repeatedly take aim at a nesting bald eagle and apparently overwhelmed it, eventually contributing to nest failure.
Migration may be the single largest seasonal flocking. Listen after dark, especially during the late summer, for dozens or hundreds of peeps and chirps coming from overhead flocks of songbirds heading south. Or listen for the honking of geese flying high in the sky during daylight hours in a "V" formation. These are wild or migratory geese that pass through each fall and spring. More familiar are local or urban geese, our resident populations, and descendants of captive geese once used by waterfowl hunters. These geese more often fly at lower altitudes, just above rooftops, and shorter distances also in formation.
Also flocks of swallows, most commonly tree swallows, may be seen by the hundreds or thousands feeding, resting or flying south in flocks in the late summer.
Sea birds and a few species of swallows, for instance, congregate for nesting and feeding. And surprising at is may sound, while not exactly flocking, some birds gather together for warmth, as do bluebirds.
Not only birds gather in flocks, so do fish, insects and some mammals, only this behavior goes by different names, according to types, as in schools, swarms or herds. Even marine mammals gather into pods.