The frogs are secretive, breed only at night, and always at the peak of monsoon season, but researchers have finally identified their remarkable mating habits

They mostly come at night. Moments after sunset, and calling as they move, the Bombay night frogs climb high into the trees that overhang rivers swollen by the warm monsoon rains in the forests of Western Ghats in India.

And then the action begins. On rain-soaked leaves, branches and tree trunks, the amphibians pair up. The female sends a willing signal by backing towards her male and touching his head with her toes. What follows is a mating position never seen before in the wild world of frog sex.

Facebook Twitter Pinterest The Bombay Night frogs in Dorsal straddle: a new amplexus mode in frogs. Photograph: SD Biju ￼

“It’s remarkable,” said Sathyabhama Das Biju, an expert on amphibians at the University of Delhi, who has published a comprehensive report on the frogs’ sexual antics. “So far, this mating position is known only in Bombay night frogs.”

It was 2002 when Biju first witnessed Bombay night frogs mating. But the animals are secretive, they breed only at night, and always at the peak of monsoon season. He got the odd glimpse, but not much else. It took eight more years for Biju to launch a study dedicated to unravelling the beasts’ mysterious breeding habits.

Now, after 40 nights in the forest, Biju has amassed enough field notes, photographs and infrared night-vision video footage from 13 encounters to describe the breeding habits of the frogs, Nyctibatrachus humayuni, in detail.

Until Bombay night frogs fell under the spotlight, scientists had identified six mating positions among the world’s 6,650 frog species. The male might clasp the female around the waist, grab her armpits, hold her head, attach himself to her back with a gluey substance, sit back-to-back, or perhaps sit on her head. But the Bombay frogs do none of these.

Facebook Twitter Pinterest Before now, scientists had identified six mating positions among the world’s 6,650 frog species. Photograph: SD Biju ￼

Writing in the journal PeerJ, Biju and his colleagues describe how they filmed males clambering on to females. What happened next was unexpected. Instead of clasping his partner, the male took hold of nearby branches or leaves to steady himself. He then appeared to release his semen on to the female’s’ back. Soon afterwards, the female shrugged the male off, and laid her eggs, which, the researchers hypothesise, are “fertilised by semen running down her back and hind legs.”



Facebook Twitter Pinterest The researchers discover their remarkable findings.

Asked why the frog might have adopted the unusual approach to mating, Biju said: “We have no idea.” But the new position does have a name: the dorsal straddle. “It differs from the other six positions because the male does not grasp the female under her armpits or head, but instead places his hands on the leaf, branch or tree trunk the pair is sitting on,” he noted.

The 5cm-long Bombay night frog is endemic to the Western Ghats, a mountain range and world heritage site that runs parallel to the west coast of India, spanning a thousand miles from Gujarat to Kerala. While males of all frog species call for mates, Biju’s field recordings reveal that female Bombay night frogs issue their own calls, making them one of only 25 frog species known to do so. He also recorded fights among males, with interlopers forcefully barged out of the way, and predation of the frogs’ fertilised eggs, with 80% of a female’s clutch being eaten by nearby snakes.