Fig. 7

The screenshots of calling postures of males of Oriental a–c and Common d–f Cuckoos. The spectrograms of calls are shown in the bottom panel (g, x-axis = time in s; y-axis = frequency in kHz), and the lowercase letters over blue arrows indicate the time position of corresponding still-frame images a–f. Common Cuckoo male produces the first note of a call with the open beak e, and the second note is produced while the beak is closed f. By contrast, Oriental Cuckoo male produces both notes with the closed beak b, and the beak is opening slightly only just before calling a. The enlargement of throat is characteristic for calling in both species (red arrows), and is the most apparent when the beak is closed. The video-recordings used for the analysis were downloaded from https://www.youtube.com/watch?v=4rq4J8i9QNo (Oriental Cuckoo) and https://www.youtube.com/watch?time_continue=11&v=wejl6ukN8yc&feature=emb_logo (Common Cuckoo)