Evolution may select certain birds that are able to produce mimicking mobbing calls and allow birds able to produce more effective alarm calls to survive, but there is also a neurological learning component from other birds. Also, "unlike children, who can learn any language they are exposed to, the musical language of most birds is somewhat constrained by their genetic heritage. Given a choice of two songs -- their own and that of another, even a closely related species -- they will learn their own. but, if exposed only to the song of another species, they will learn a version of it" (Brody, 1991:1). Thus, birds can develop certain species specific calls, like alarms, but also can within some constraint learn calls that sound the same and are recognizable to other species. Functionality is also an issue, as songs for mating, as discussed by Brody (1991) only have use in...
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