Experimental setup for periods of food manipulation and mate choice experiments (a) period of experimental food manipulation.

<p>Offspring were kept in the adjacent aviaries with one adult male as song tutor centered between the aviaries. The front of each aviary was made of mesh wire, the other parts of plywood. (1) Offspring aviaries had a perch in the rear (4) and a perch in front of the tutor (5). The separation between the two aviaries had mesh wire (2) instead of plywood between the frontal perch (5) and the front panel. Thus, offspring of the two groups could be in visual and acoustic contact to each other. Food and water was provided in dishes and differed in adjacent aviaries according to the two nutritional treatments. Overall nine of such setups were used, all located in the same experimental room. (b) mate choice experiments. Females could move freely in the large free-flight aviary. Two cages (2) with males that came from two adjacent aviaries (as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000901#pone-0000901-g001" target="_blank">Figure 1a</a>) were placed in the top rear corners of the aviaries. Females were provided with food and water (1) and perches in a neutral zone (3). Perches of male cages extended into the female cage (4) so that females could perch directly in front of either male (preference zone) without being able to see the other male. Males could not see each other due to a visual barrier between cages. Drawings are partly to scale. See text for further details