Supplementary Figure 14: Sound amplitudes of vocalizations measured with near and far backpack microphones and distances between animals during songs and calls

Four panels (a-d) show median sound amplitudes during vocalizations of birds 1-4 recorded with microphones 1-4. Standard errors are estimated by bootstrapping. Sound amplitudes are reported in units of air pressure mPa (1 mPa = 10^-3 H/m²). Note that on average song vocalizations were 3.16 ± 0.80 times louder than calls (amplitude, mean ± s.e.m). The ratio of amplitudes on vocalizing and listening birds’ microphones was used to estimate the distance between animals, assuming a fixed distance between the beak and the backpack microphone in the vocalizing bird (∼3 cm). The four panels (e-h) show median distances between vocalizing birds 1 - 4 and all listeners when the vocalizing animal was either calling or singing. The shown standard errors were estimated by bootstrapping. Note that bird 1 kept a large and similar distance with all other birds during calling and singing (e). Bird 2 was closer to other birds during calls, but when singing it was closer to bird 1 and further away from bird 4 (f). The co-singing birds 3 (g) and 4 (h) were closer to other animals during singing than during calling. *P < 0.05, **P < 0.001, bootstrap.