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They observed something yet to be recorded by scientists: male frogs straddled across the backs of females, with minimal physical contact. Where frogs normally grab females with their front legs, the frogs were instead taking hold of branches or leaves. And when the acts were finished, after an average copulation time of about 13 minutes, the females arched their backs rhythmically to signal the males to leave.

The researchers also recorded a distinct mating call that males used more frequently as females moved nearer.

The study provides a detailed view of frog mating behaviour, expanding the list of six sex positions — used by nearly 7,000 frog species around the world — to seven. It also confirms that frogs can be defensive of newly-inseminated eggs. In one video, a frog defends his seeded clutch from another approaching male.

But why the dorsal straddle? Researchers say that while they can only speculate, the position could provide two key advantages.

First, rather than gripping the female, latching onto a branch could be more stable, and lower the risk of falling. Even so, researchers noted that in half of the events, either one or both frogs dropped into the stream below. Some were able to climb back up and continue where they left off.

Second, as was also suggested by a 2010 study, the pulsating movements against the females’ backs could stimulate ovulation.

Frogs are known as “indicator species,” which means they are particularly sensitive to environmental changes. They are often the first to be negatively affected by disease outbreaks or increased pollution.

The researchers say that understanding these sensitive species could help to develop conservation efforts in west India, where conversion of forest to agricultural areas and water pollution by chemical fertilizers pose a serious threat to species diversity.

“A good understanding of each species’ ecology, including reproduction, is of major importance for planning and successfully implementing conservation strategies,” the researchers noted.

“Additional studies further exploring the unique and diverse behaviour in Nyctibatrachus frogs are, therefore, badly needed.”