The Amazing Spectacle of Grackle Flocks

This is the time of year when birds can surprise you just by their sheer numbers. For many species, it is time to flock together and appear to be friends. Around here, we are most likely to see large groups of starlings, crows, or Canada geese, but there are other species as well.

These flocks can be quite secretive and even mysterious. Take a walk in a field overgrown with bushes and grasses and stop by a brush pile hidden by tall weeds. All might be silent with not a feather stirring. Make a hissing noise, however, and from the depths of the brush, where they had been feeding quietly on fallen seeds, the little juncos rise like gray ghosts.

They sit in the open at the top of the pile and twitch their tails nervously, showing off the white outer tail feathers. The gentle tinkle of their tiny voices fills the air, building to a chorus as the flock grows to forty or fifty birds, all coming closer to find the source of the noise.

Once this fall, there was a louder clack note that caught my ear among the junco voices. A larger bird, which first appeared to be a mockingbird, was in a small tree among the juncos. It turned out to be a shrike, a predator of the small juncos, but they ignored their enemy as they slowly flew off and melted away again into the dense groves.

There have also been flocks of blackbirds around, these birds more obvious, ranging across the skies, especially in the late afternoon or early morning. They will appear suddenly overhead, heralded by their noisy chucking, which can be heard a mile away if there are enough birds.

Often, the first hundred or two suddenly becomes a stream that stretches into the high horizon. They pop into view in growing numbers as the lead birds are already disappearing in the opposite distance. The hill in Granville, where watchers are still counting migrating hawks during the day, has been in the flight line of a huge congregation of grackles.

One late afternoon, the watcher estimated a broad line of grackles flying toward the southeast numbering about 125,000 birds. The day before this, and a few miles away in Southwick, another startled yard raker looked up and witnessed a similar flight that she said seemed like 'millions.'

These grackles are staging for a massive flight farther south, where flocks and roosts of several million have been known to form, descending on the snowless countryside by day and gathering in a dense grove of tall evergreens by night. If this happens near human habitations, the alarm of nearby residents leads to measures aimed at disturbing or moving the roost.

Gathered together as they are, these birds do not do it for friendship. In fact, it is a syndrome known as the 'geometry of the selfish herd.' Each bird benefits from the flocking by reducing its exposure in the 'domain of danger,' where a predator might pick off a single bird at the edge of the flock.

In a roost, the experienced and healthy birds take the center of the flock, leaving others on the outer edge. In turn the younger birds benefit by having the veterans lead them to good foraging grounds during the day. As the young birds survive each year, they gradually move in to the center for a safer night's sleep.

Such flocks can be disruptive to both man and nature. In Africa, a bird called the red-billed quelea will swarm in the many millions, and flamethrowers have been used to control them when the crops of an entire region have been threatened. The quelea is a weaver finch, a close relative of the house sparrow, which is trouble enough at our feeders in their flocks of fifty or more.

The largest flocks on record belong to North America, where masses of passenger pigeons once darkened the sky as they flew. As many as several billion birds would descend on a single place in a nesting colony which would encompass square miles of soon-devastated countryside. The birds would move on and nature survived, as the pigeon did until man's assault with firearms. Flocking together did not protect this bird from the ultimate predator.