Vocal development and voice breaking in Demoiselle Cranes (Anthropoides virgo)

Abstract

The vocal development of cranes (Gruidae) has attracted scientific interest due to a special stage, so-called voice breaking. During voice breaking, chicks produce both adult low-frequency and juvenile high-frequency vocalizations. The triggers that affect voice breaking are unknown. For the first time, we study the vocal development of the Demoiselle Crane (Anthropoides virgo). We describe the age and possible drivers of the onset of voice breaking. We analyse the calls of 21 Demoiselle Crane chicks, and compare them with the calls of six adult birds, noting the day when adult low-frequency calls are first recorded as the day when voice breaking begins. The age of voice breaking onset does not depend on hatching date, clutch order or chick body mass. Thus, there is no correlation between body growth and the onset of voice breaking for individual Demoiselle Crane chicks. However, there is a strong relationship between body mass and voice breaking among different crane species. Demoiselle Cranes stop intense body growth at the age of 2 months and start voice breaking at 70 ± 46 days. By way of comparison, Red-crowned Cranes finish the period of intense body growth at the age of 7 months and start voice breaking at 211 ± 60 days. Thus, we show that the Demoiselle Crane has a sudden vocal development, similar to other crane species, and we suggest that the end of intense body growth is the trigger for the onset of voice breaking in cranes.