Voice breaking and its relation to body mass and testosterone level in the Siberian Crane (Leucogeranus leucogeranus)

Vocal development of cranes (Gruidae) has attracted scientific interest due to its special stage, voice breaking. During voice breaking, chicks of different crane species produce calls with two fundamental frequencies that correspond to those in adult low-frequency and juvenile high-frequency vocalizations. However, triggers that affect voice breaking in cranes are mainly unknown. Here we studied the voice breaking in the Siberian Crane (Leucogeranus leucogeranus) and test its relation to the body mass and testosterone level. We analyzed 5846 calls, 39 body mass measurements and 60 blood samples from 11 Siberian Crane chicks in 8 ages from 2.5 to 18 months of life together with 90 body mass measurements and 61 blood samples from 24 Siberian Crane adults. The individual duration of voice breaking and dates of its onset, culmination and completion depended neither on the body mass nor on the testosterone level at various ages. But we found correlation between the testosterone level and mean deltas of percentages of the high and low frequency components in Siberian Crane calls between the closest recording sessions. We also observed some coincidence in time between the mean dates of voice breaking onset and the termination of body mass gain (at 7.5 months of age), and between the mean dates of voice breaking completion and the start of a new breeding season. Similar relations have been shown previously for some other crane species. We also showed for the first time that the mean dates of voice breaking culmination correlated with the significant increase of the testosterone level (at 10.5 months of age). So, we suggest that voice breaking in cranes may be triggered by the end of chicks’ body growth, is stimulated by the increase of testosterone level and ends soon after adult cranes stop taking care of their chicks.