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We do not know how vocal learning came to be, but it is such a salient trait in human evolution that many have tried to imagine it. In primates this is difficult because we are the only species known to possess this skill. Songbirds provide a richer and independent set of data. I use comparative data and ask broad questions: How does vocal learning emerge during ontogeny? In what contexts? What are its benefits? How did it evolve from unlearned vocal signals? How was brain anatomy altered to enable vocal learning? What is the relation of vocal learning to adult neurogenesis? No one has described yet a circuit or set of circuits that can master vocal learning, but this knowledge may soon be within reach. Moreover, as we uncover how birds encode their learned song, we may also come closer to understanding how we encode our thoughts. (Contains 8 figures.)

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2005.09.013 Byline: Noam Leader, Fernando Nottebohm Abstract: We investigated the effect of social variables on the regulation of the moult from juvenile to adult plumage in male zebra finches. Males reared in social isolation after day 31 after hatching retained their juvenile plumage until day 90; if then placed in a colony setting, they developed the typical male plumage in 2-3 weeks. The isolation-induced delay in male plumage resulted from a delay in the juvenile moult. Social isolates that could trigger song playbacks by pecking at a key developed male plumage at the same time as controls. We suggest that a nongonadal mechanism sensitive to social variables normally ensures that adult male plumage is acquired in zebra finches during the weeks leading up to sexual maturity. This is the first report of a social effect on moult. Author Affiliation: Rockefeller University Field Research Center Article History: Received 30 October 2004; Revised 21 December 2004; Accepted 12 September 2005 Article Note: (miscellaneous) MS. number: 8324

Does the ontogeny of vocal imitation follow a set program that, given a target sound, unfolds in a predictable manner, or is it more like problem solving, with many possible solutions? We report that juvenile male zebra finches, Taeniopygia guttata, can master their imitation of the same song in various ways; these developmental trajectories are sensitive to the social setting in which the bird grows up. A variety of vocal developmental trajectories have also been described in infants. Are these many ways to learn unique to the vocal domain or a hallmark of advanced brain function? learning strategy | social influence | vocal learning | zebra finch

The high vocal center (HVC) of adult male canaries, Serinus canaria, is necessary for the production of learned song. New neurons are added to HVC every day, where they replace older neurons that have died, but the length of their survival depends on the time of year when they are born. A great number of HVC neurons born in the fall, when adult canaries learn a new song, are still present 8 mo later, when this song is used during the breeding season. By contrast, most of the neurons born in HVC in the spring, when little song learning takes place, disappear much sooner. Here we show that infusion of brain-derived neurotrophic factor into HVC during days 14-20 after new HVC neurons are born in the spring confers on them a life expectancy comparable to that of fall-born neurons; this extension on life is not seen when infusion occurs 10 days earlier or later. We suggest that there is, in the adult HVC, a subset of neurons whose life expectancy is determined by brain-derived neurotrophic factor during a sensitive period soon after these neurons reach destination and start forming connections.