Sarus cranes typically live most of their lives as a male-female duo, singing tightly coordinated duets. At a glance, the male and female, both standing 1.5-1.8 meters (5-6 feet) tall, are difficult to tell apart visually. They’re both gray-bodied with red necks and head. But researchers have found a way of distinguishing between the sexes through the notes they sing in their songs, reports Mongabay India’s Kartik Chandramouli.
Being able to accurately tell between a male and a female of a species, such as the sarus crane (Antigone antigone), a species considered vulnerable to extinction, is crucial for understanding several aspects of its life: from the sex ratio of its populations and the sex-specific roles the individuals play in the wild, to how human activities influence the two sexes, all of which can ultimately help inform conservation actions.
So, for more than six months, researcher Suhridham Roy spent his time in agricultural fields in the Indian states of Gujarat, Haryana and Uttar Pradesh, observing and recording 215 duets from 136 breeding bird pairs of sarus cranes.
Roy and his colleagues analyzed the recorded duets as graphs called spectrograms. Each duet consists of an introduction, trill and the main section. The analysis, published in a recent study, showed that the male and female portions within each section — cross-referenced with careful field observations — varied significantly and had distinct acoustic signatures. Male notes tended to be longer, lower-pitched, with wider modulation. Female notes were brief, higher-pitched, and sharper.
“Identifying sex is a bigger problem in non-breeding flocks that don’t perform duets but are constantly vocalizing and form 50-70% of a population in an area,” study co-author K.S. Gopi Sundar, Roy’s Ph.D. mentor who has studied these cranes since 1998, told Chandramouli. He added the study offers baseline data to train machine-learning models to identify sexes in non-breeding birds, currently a major research gap.
Ecologist John Grant, who studies sarus cranes in northern Australia, told Chandramouli the acoustic sexing method developed using Indian sarus cranes can be used for all the subspecies. Sarus cranes can be found in the wetlands of Pakistan, Nepal and Myanmar, as well as the forests of Southeast Asia and Australia.
Mongabay India previously reported in a podcast episode that every sarus crane pair’s duet is acoustically unique, and used to reinforce bonds and announce the boundaries of their territories to other crane pairs.
While sarus cranes are typically monogamous, Sundar, Roy and researcher Swati Kittur also found that sometimes sarus crane pairs bring in a third crane into their closely knit families, singing unison calls called a triet. The presence of triets in a landscape can indicate poor habitat quality, where the third crane is essentially a helping hand, invited in to increase the chicks’ survival.
Read the full story by Kartik Chandramouli here.
Banner image: A sarus crane pair sings a duet. Image by Ad031259 via Wikimedia Commons (CC BY 4.0).
