Many species of birds are extremely adept at mimicking both the calls of other birds, and other animal and non-animal sounds. Notably parrots and Minah birds - but also documented in blackbirds, bower birds, sparrows, lyrebirds, robins, owls etc etc.
Over the past few decades, numerous research studies have attempted to explain why such skills might have developed.
Theories include :
• Beau Geste hypothesis (birds pretending to be other species in order to deceive others that their territory is bigger than it actually is)
• Batesian Acoustic Mimicry (the idea that mimics may deter competitors or potential predators by copying the vocalizations of animals that are predatory or agonistic)
• Attracting a Third Species (mimics might benefit by inducing mobbing of their own predators or competitors by individuals of one or more other species)
However, an extensive review of such research was published in the journal Animal Behaviour in 2008, finding that :
“With few exceptions, our understanding of the function and acquisition of this fascinating behaviour seems to have scarcely progressed. […] We conclude that there is no compelling evidence to support any of the functional hypotheses but, rather, that almost all of the data concerning song mimicry are consistent with the learning mistakes hypothesis, whereby birds learn simple and common sounds, frequently using them in inappropriate contexts. Additionally, many apparently mimicked sounds are calls, not songs, which themselves may not be learned by the models. ”
A later study (2014) noted that :
“Vocal mimicry is poorly understood despite being widespread amongst birds. Our understanding of the evolutionary dynamics of vocal mimicry has been hampered by a severe lack of observational, descriptive and experimental data on mimics, models and receivers, as well as conceptual confusion over the definition of mimicry.”
See: Avian vocal mimicry: A unified conceptual framework in Biological Reviews, July 2014