Beecher (2008), however, cautions that sharing patterns may result solely from a simpler, underlying rule by which young males learn the songs they hear most often and most clearly. The song-learning rules emphasized above seem designed to maximize the sharing of songs between neighbors, implying that song sharing is selectively advantageous. Once the repertoire of song types is crystallized at 1 year of age, it does not change thereafter ( Nordby, Campbell, & Beecher, 2002). A young male is especially likely to retain in his repertoire songs that are sung by neighbors that survive into his first breeding season, often biasing his final repertoire toward one particular neighbor's repertoire ( Nordby et al., 1999). Young males learn songs from multiple males encountered during this period ( Beecher, Campbell, & Stoddard, 1994 Nordby, Campbell, Burt, & Beecher, 2000 Nordby et al., 1999, 2001), preferring to learn songs that are sung by more than one potential neighbor ( Beecher, Campbell, & Stoddard, 1994 Nordby et al., 1999, 2001). During the period in which they learn their songs, young males visit as many as 30–40 territories, gradually reducing their home ranges from their natal summer to the subsequent spring, when their home ranges become normal-sized territories ( Templeton, Reed, Campbell, & Beecher, 2012). Males in this population learn songs from potential neighbors after natal dispersal, that is, after they have left the territories where they were born and have moved to the areas where they will establish their own territories ( Beecher, Campbell, & Stoddard, 1994 Nordby, Campbell, & Beecher, 1999). Patterns by which songs are culturally transmitted have been worked out for a nonmigratory population of song sparrows in Seattle through a combination of field and laboratory studies ( Beecher, 2008 Nordby, Campbell, & Beecher, 2001). Because a song repertoire adapted for territory defense is presumably one of the chief outcomes of song development, the song-learning strategy of song sparrows has implications for our understanding of how song functions in territory defense in this species. Song learning appears to be universal in songbirds, but strategies for learning vary substantially among songbird species ( Beecher & Brenowitz, 2005). Song sparrows reared in acoustic isolation from other individuals develop abnormal songs ( Kroodsma, 1977 Marler & Sherman, 1985), whereas young males exposed either to recorded songs or to live tutors produce songs that closely resemble species-typical adult song ( Beecher, 1996 Marler & Peters, 1987). Beecher, in Advances in the Study of Behavior, 2014 2.3 Song Learning
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