Alarm signal

In the field of animal communication, an alarm signal is an antipredator adaptation referring to various signals emitted by social animals in response to danger. Many primates and birds have elaborate alarm calls for warning conspecifics of approaching predators. For example, the characteristic alarm call of the blackbird is a familiar sound in many gardens. Other animals, like fish and insects, may use other non-auditory signals, such as chemical messages. While visual signs have been suggested as alarm signals, they are easier to pinpoint by predators and less likely to be received by conspecifics, so have tended to be treated as a signal to the predator instead. An animal who signals an alarm is called an alarmer.

Different calls may be used for predators on the ground or from the air. Often, the animals can tell which member of the group is making the call, so that they can disregard those of little reliability.

Evidently, alarm signals promote survival by allowing the receivers of the alarm to escape from the source of peril, but this ecological safety system may come at a cost to the signaller. When an animal calls attention to itself by signalling, it may be more likely to be eaten by a predator than if it had kept quiet. This intuition has been verified by experimental data on ground squirrel predation rates and the connection between this and the noisy chirping or whistling alarm calls. However, there is also some evidence that alarm calls can increase individual fitness as well.

Alarm calls are often high-frequency sounds because these sounds are harder to localize, despite common belief.

This cost/benefit tradeoff of alarm calling behaviour has sparked many interest debates among evolutionary biologists seeking to explain the occurrence of such apparently "self-sacrificing" behaviour. The central question is this: "If the ultimate purpose of any animal behaviour is to maximize the chances that an organism's own genes are passed on, with maximum fruitfulness, to future generations, why would an individual deliberately risk destroying itself (their entire genome) for the sake of saving others (other genomes)?".

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