Fig. 1.

The dawn chorus ritual of great tits (Parus major) peaks with female fertility. (A) Sonogram of a stereo recording shows the acoustic interaction between a male (song in blue) and a female (calls in red). Males continuously sing or call close to the nest box during dawn, and females can call in response. Females call mostly at the start of male dawn singing, during song type switches, and shortly before emergence from the nest box. Upper and Lower show recordings made with the outside and inside microphones, respectively. (B) Within individual variation of great tit song behavior is related to egg laying (GLMM; **P < 0.001), and males sing lowest when fertility is highest (egg day −1). (C) Female calling changes with egg laying (GLMM; ***P < 0.001), and females call most on days around the start of laying. The graphs show means ± 1 SE. The x axes show days related to start of laying (egg day 0; indicated by barred line), and y axes show male average weighted frequency of low notes and female calling (number of calls produced during dawn chorus, normalized per female).