As birds flock together this time of year I get drilled with questions on the topic and evidently last month’s article didn’t answer all the questions. Whether it’s a congregation of crows, a swarm of shorebirds or a gaggle of geese, we want to know why birds flock.
Perhaps you’ve noticed bushtits bouncing like gray puff balls from bush to tree to shrub as they move through an open deciduous forest. They form into loose flocks and wander along with no apparent agenda other than happily sampling insects and grubs.
Or perhaps you’ve observed tight flocks of shorebirds performing aerial displays, alternately flashing their dark backs and white bellies, as they move in one undulating cloud over Deer Lagoon or Crockett Lake.
Birds flock for several reasons. They flock for more efficient feeding. The more eyes looking for rich feeding areas, the more likely an area will be found. Also, a group of birds can overwhelm other individual birds that may have established a feeding territory.
However, the main reason small birds flock is to minimize vulnerability from predators.
For most birds, the first defense against predators is hiding. Birds have developed into fast fliers for just this purpose. They zip into trees, scurry into thick brush, or just get the heck out of the way. But hiding is not always an option. So flocking developed as the next best line of defense.
Think about it. A bird by itself must be alert to attack from all sides at all times. If little Tweety spends a large part of the day watching for predators, little time is left for eating. But two birds feeding side by side theoretically can cut their watching time in half, and spend more time searching for food. Now put these two birds into a flock of 10 or 25 or 100, and their feeding time increases exponentially.
Also, flock movements can confuse an attacking predator.
This is one reason, presumably, why shorebirds fly in a tight swarm. It has been suggested that a huge undulating cloud of shorebirds gyrates to distract the attacking peregrine falcon and makes it more difficult for the attacker to pick out one bird. If you carefully watch these clouds of shorebirds the largest mass of birds within the flock seems to shift away from the attacker leaving a smaller domain of danger, the spot closest to the attacker.
Smaller passerines often form into mixed species flocks. Near-sighted gleaners, such as vireos and warblers, flock with far-sighted salliers like flycatchers, thereby taking advantage of the latter’s better vision. Constant chattering among flock members keeps the flock together and one alarm call scatters the group to seek shelter.
There is one more advantage of flocking as a defense from predators. Again, it’s the safety in numbers game. A lone bird is a sitting duck exposed on every side. However, if our bird is so wise as to join a flock, it is exposed to predation from a fraction of the possible directions. The larger the flock, the greater the chance of a given individual not ending up as lunch.
Do the birds also flock together for purely social reasons, such as we do over the holidays? No one has ever proven that, but from our perspective their constant vocalizations seem to suggest that they might.
On Dec. 30, the Whidbey Audubon Society will be conducting the first South Whidbey Christmas Bird Count. We’ll be counting birds from just north of Greenbank down nearly to the south end of the island. Watch for teams of birders scanning the skies, forests and beaches looking for all our winter birds, those flocking as well as those going solo.