Seasonal changes in testosterone, neural attributes of song control nuclei, and song structure in wild songbirds. The Journal Of Neuroscience : The Official Journal Of The Society For Neuroscience, 17(15), 6001-10. Retrieved de http://www.jneurosci.org/cgi/pmidlookup?view=long&pmid=9221796 (Original work published 1997)
. (1997).