Figure 8. Timeline of trials.
Timeline indicating housing conditions and approximate timing of backpack application, habituation phase (minimum 7 days), beginning of trial and sound recordings (ca. 3 weeks, see ‘Materials and methods’), onset of nest material availability, end of trial. Of the continuous sound recordings, mornings (220 ± 20 min) of different days (differed between trials, not indicated in graph) equally representing birds' breeding stages were analysed. Blood sampling occurred three times (indicated by red arrows): before the beginning of the trials, 1 day after males and females were joined and 1 day after nest material became available.