In the current issue of Trends in Cognitive Sciences there is an interesting (and free!) review of the linguistics of birdsong and its similarities and differences to human language:
Unlike our primate cousins, many species of bird share with humans a capacity for vocal learning, a crucial factor in speech acquisition. There are striking behavioural, neural and genetic similarities between auditory-vocal learning in birds and human infants. Recently, the linguistic parallels between birdsong and spoken language have begun to be investigated. Although both birdsong and human language are hierarchically organized according to particular syntactic constraints, birdsong structure is best characterized as ‘phonological syntax’, resembling aspects of human sound structure. Crucially, birdsong lacks semantics and words. Formal language and linguistic analysis remains essential for the proper characterization of birdsong as a model system for human speech and language, and for the study of the brain and cognition evolution.
(2011) "Songs to syntax: the linguistics of birdsong." In: Trends in Cognitive Sciences." Volume 15, Issue 3, March 2011, Pages 113-121