Publications

Abstract

Vocal development of cranes (Gruidae) has attracted scientifc interest due to its special stage, voice breaking. During voice breaking, chicks of diferent crane species produce calls with two fundamental frequencies that correspond to those in adult low-frequency and juvenile high-frequency vocalizations. However, triggers that afect 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 frst time that the mean dates of voice breaking culmination correlated with the signifcant 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.

Abstract

Vocal-based monitoring is increasingly being used as a non-invasive method for identifying individuals within avian populations and is promising for the Siberian Crane, Leucogeranus leucogeranus. This is a poorly studied, long-lived, secretive and critically endangered bird species that breeds in the Arctic tundra of western and eastern regions of Siberia. We assessed between- and within-year stability of individual-specific vocal features in duets of Siberian Crane and tested the effect of pair-mate change on their stability. Previous findings showed that duets are specific to different pairs of birds; however, it is still unknown how long pair-specific traits of duets remain and if they change in the course of a year or when birds re-mate. We recorded duets of 15 reproductively active pairs in the Oka Crane Breeding Centre in 2003–2006 and 2013–2017. We found that pair-specific vocal signatures remained stable both within the year and across ~ 10 years. After a change of mate, most of the variables we measured in the call did not change in any of the birds. Our data suggest that the stability of the
individually specific vocal features may enable Siberian Cranes to be reliably identified by their duets over the birds’ lifetime. We believe that our work can increase confidence in the use of acoustic recognition techniques for endangered crane monitoring programs. Our results also suggest that Siberian Cranes may use their duets to form long-term social bonds between neighbours.