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Animal alarm calls are an aspect of animal distress calls and animal vocalization. The term refers to various vocalizations that they emit in response to danger. Many primates and birds have elaborate alarm responses for warning other animals of the same species about approaching predators. For example, the blackbird’s characteristic alarm call is a familiar sound in many gardens.
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[How to reference and link to summary or text].
Evolutionary psychology perspective
Evidently, alarm calls promote survival by allowing the hearers of the alarm to escape from the source of peril, but this ecological safety system comes at a high cost-- to the caller. When an animal calls attention to itself by making a noisy alarm, it is much 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.
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 themselves (their entire genome) for the sake of saving others (other genomes)?".
Some scientists have used the evidence of alarm-calling behaviour to challenge the theory that "evolution works only/primarily at the level of the gene and of the gene's "interest" in passing itself along to future generations." If alarm-calling is truly an example of altruism, then our understanding of natural selection becomes more complicated than simply "survival of the fittest gene". This feature of alarm-calling behaviour is taken to suggest that evolution by natural selection is not capable of explaining some behaviours , or else that evolution has the capacity not just to select at the genetic level, but also at the species level.
Other researchers, generally those who support the "gene's interest only" theory, question the authenticity of this "altruistic" behaviour. For instance, it has been observed that yellow-bellied marmots sometimes emit calls in the presence of a predator, and sometimes do not. Studies show that these marmots may call more often when they are surrounded by their own offspring and by other relatives who share many of their genes. Other researchers have shown that some forms of alarm calling, for example, "aerial predator whistles" produced by Belding's ground squirrels, do not increase the chances that a caller will get eaten by a predator; the alarm call is advantageous to both caller and recipient by frightening and warding off the predator.
In addition many of these auditory signals have characteristics that make it difficult for potential predators to identify the whereabouts of the caller. For example many calls begin and end gradually which makes it more difficult to compare the times at which the sound reaches the predators ears which makes localization of the source problematic. Many alarm calls are also low in pitch which makes it harder to locate than high pitched sounds. Many birds, for example, emit low pitched, continuous alarm calls, which begin and end gradually. Many calls are so similar in this regard that the can also warn members of other species. 
Considerable research effort continues to be directed toward the purpose and ramifications of alarm-calling behaviour, because, to the extent that this research has the ability to comment on the occurrence or non-occurrence of altruistic behaviour, we can apply these findings to our understanding of altruism in human behaviour.
- McFarland, D (2006). Oxford Dictionary of Animal Behavior. Oxford University Press. Oxford.
- Chickadees' alarm-call carry information about size, threat of predator
- The Trek of the Pika "A story complete with sounds of pika and marmot calls" 2002-10-30
- Characteristics of arctic ground squirrel alarm calls Oecologia Volume 7, Number 2 / June, 1971
- Why do Yellow-bellied Marmots Call? DANIEL T. BLUMSTEIN & KENNETH B. ARMITAGE
Department of Systematics and Ecology, University of Kansas