22/02/2017 3:43 PM IST | Updated 22/02/2017 4:42 PM IST

Four New Species Of World's Smallest Frogs Discovered In The Western Ghats

They're so tiny that they can even sit on a human fingernail.

SD Biju

A team of scientists from Delhi has discovered seven new frog species, four of which are so small that they can perch on a coin or a human fingernail. Found in the Western Ghats in Kerala and Tamil Nadu, these are among the smallest-known frogs on earth.

All the new species are known as night frogs, and belong to the genus Nyctibatrachus. Night frogs are an ancient group of frogs endemic to the Western Ghats, which diversified approximately 70 to 80 million years ago. The discovery brings the total number of known night frogs to 35. Four of these are among the smallest Indian frogs, and measure between 12.2 to 13.3 mm in length.

The findings are the culmination of five years of extensive field exploration by Delhi University professor Satyabhama Das Biju, also known as the Frogman of India, and his PhD student Sonali Garg, along with two others. "These findings are evolutionarily significant, because the abundance and diversity of miniature forms are much higher than believed to be earlier," Garg said. "Now nearly 20 percent of night frogs have been found to be miniature."

Though these miniature frogs are fairly common, finding them was tricky business. They remained undetected until now not just due to their tiny size, but also secretive habitats and insect-like calls. "They hide under leaf litter and marsh vegetation," Garg said. "Their calls are not frog-like but like insects, so even if scientists are walking across the forest floor, they are mistaken as insects." On one occasion, Das and his team were so engrossed in listening to a frog call that they ignored an elephant's trumpet and ending up getting chased by the animal.

A global biodiversity hotspot, the Western Ghats has an extraordinary diversity of amphibians. Nearly 103 of the 1,581 frog species discovered between 2006 and 2015 all over the world were found in the Western Ghats region. "It is a haven for different species, with a wide range of habitats being found in the region," Das said.

Even as they celebrate the discovery of these new miniature frogs, Das warns that many of the frogs face serious threats due to loss of habitat caused by human activity. "At least five of the seven new species are vulnerable because they lie outside the protected regions," Das said. "Apart from this, over 32 percent, that is one-third of the Western Ghats frogs are already threatened with extinction."

For instance, one of the new species was named the Athirappally night frog since it was discovered close to Kerala's Athirappally waterfalls, the site for a proposed hydroelectric project. Another species called the Sabarimala night frog was discovered near the Sabarimala temple, which is located inside the Periyar Tiger Reserve. Yet, since the temple attracts a lot of pilgrims, there is considerable human disturbance near the frog's habitat. Other habitats lie in plantations.

"Today, frogs are facing extinction simply because of humans," Das said. "Habitat destruction, fragmentation and loss are major threats for amphibians not just in India, but all over the world."