Graduate student Nick Mason and collaborators recently published a paper in Evolution about diversification, rates of song evolution, and vocal learning in passerine birds. By combining two large vocalization data sets, this study finds a positive association between accelerated bursts in speciation and vocal evolution. Furthermore, the authors find evidence that songs evolve faster in tangagers, which learn their songs through cultural transmission, compared to ovenbirds and woodcreepers, which have innate song.
Mason, N. A., Burns, K. J., Tobias, J. A., Claramunt, S., Seddon, N., & Derryberry, E. P. (2017). Song evolution, speciation, and vocal learning in passerine birds. Evolution. http://doi.org/10.1111/evo.13159d