Birdcalls of Alarm

Many birds produce both extended songs and brief calls. A bird's vocal repertory may total a dozen or more songs and calls, each having a different sound pattern and serving a distinct function. Among the calls, none is more important than the call of alarm.

Birdcalls of alarm fall into three broad categories: subtle, short-distance calls that have a specific purpose and are hard to locate; loud shrieks that provide a general warning of a nearby predator; and raucous rattling calls that may scare off a predator.

An example of the first category, subtle calls for a specific purpose, is the alarm call of the North American black-capped chickadee. When a predator approaches, the chickadee emits a high-pitched, prolonged sound with a gradual crescendo and decrescendo in volume. The lack of stops and starts in the sound confuses the predator, and it does not know which direction to attack. The calls are just loud enough to reach the chickadee's own flock, but they are not aimed at the flock members or even at the bird's own offspring, which often flee from danger to other flocks many miles away. Instead, the chickadee's alarm calls are aimed only at its mate. Chickadees have a long-term monogamous mating system, and by protecting each other from predators, pairs of chickadees ensure their continued breeding.

The second category of birdcall alarms, loud shrieks of general warning, is exemplified by the redshank, an Old World sandpiper that nests mainly in swamps. Some bird observers call the redshank "the sentinel of the salt marsh" because its clear screech of despair warns all the nearby animals, birds and others, of approaching danger.

The third category of birdcall alarms, rattling calls to scare off a predator, includes the aggressive clattering of the American blue jay. The blue jay vocally "attacks" intruders, both animals and humans, often beginning singly and gradually inducing a chorus of other birds to join the sonic battle. Various members of the thrush family have a similar alarm call.