Temporal domain dynamics in Bengalese finch songs:
Female preference and Evolution

Kazuo Okanoya
(Chiba University and PRESTO, Japan Science and Technology Corporation)

In passerine birds, song is a learned behavior used by males to attrac
t females and to repel rivals. Generally, a song is composed of several types of song notes and the order of these notes is stereotyped. However, unlike the most of songbirds studied to date, Bengalese finches sing complex songs with several possible patterns of note-to-note transitions.
The Bengalese finch is a domesticated strain of the white-backed munia. Japanese Daimyo had imported white-backed munias 250 years ago and the birds had been domesticated in Japan. We compared songs of Bengalese finches and white-backed munias and found that the temporal domain dynamics was absent in white-backed munias. So why domesticated Bengalese finches sing such complex songs? By domestication, the cost of singing complex songs should be reduced because the risk of predation and the cost for foraging are reduced. This might account for a part of the puzzle.
To answer from the functional point of view, we examined whether the temporal domain dynamics affect female reproductive behavior and physiology. Female Bengalese finches were individually kept in a small cage supplied with pot nest and nesting materials. When stimulated by a syntactically complex song, females carried more nesting materials and their E2 level after the experiment was higher than when stimulated by a simple song without temporal domain dynamics.
Next, to answer from the evolutionary point of view, female white-backed munias were kept and stimulated by a complex Bengalese finch song, simple white-backed munia song, or a white-backed munia song edited so that it had a temporal domain dynamics. The last stimulus was most effective in inducing reproductive behavior from white-backed munia females, suggesting that the tendency to prefer complex song syntax could be traced back to the wild strain even though wild type males do not sing syntactically complex song.
Taken together, we propose hypothesis that could account for the evolu
tion of complex song syntax in Bengalese finches. 1) Domestication freed Bengalese finches from the cost of singing complex songs, 2) females had sensory bias to prefer complex song patterns, and 3) the tendency to sing temporally dynamic songs was selected by females.

(Work supported by JST)