Central Ridge important habitat of rare frog, Delhi's smallest vertebrate: Study

The Microhyla nilphamariensis was first discovered in 2015 in Bangladesh and was recognised as a distinct species in Delhi only in 2019

Scientists researching the Microhyla nilphamariensis frog — Delhi’s smallest known land vertebrate, which is a locally threatened species — have discovered a healthy colony of more than 100 individuals in the Central Ridge, according to a study published in the global journal PeerJ.

The frog is only between 20 to 25mm in length, and is rarely found in Delhi. (HT photo)

The frog is only between 20 to 25mm in length, and is rarely found in Delhi, barring some sightings at Asola and JNU, making the Central Ridge an important habitat for the tiny amphibian, the study published on March 29 said.

The Microhyla nilphamariensis was first discovered in 2015 in Bangladesh and was recognised as a distinct species in Delhi only in 2019 — till then, this frog was believed to be Microhyla ornata, another similar species.

During their study — held over a six-year period between 2015 and 2021 — the researchers, led by a team from Delhi University’s Venkateshwara College, also studied the vocal acoustic repertoire of the frog, finding it to be making four distinct calls – only one of which was identified as a breeding call. The study said that the remaining three vocal calls have never been documented, and their purpose is still unknown, requiring further analysis.

The study included participation from the University of California in the US, the Centre for Advanced Learning in Mangalore, St Joseph’s College in Kerala, and DU’s SGND Khalsa College.

“Individuals were mostly found to call in grass and leaf litter, up to distances ranging from 0.5 to 20 m from the pond. Calling activity was observed to be synchronised with rainy days. A few individuals started calling shortly after sunset and within an hour, choruses were established. On an average the chorus size comprised of about 80–100 individuals spread across the pond,” said the research paper.

“Further, we compare the vocal repertoire of M nilphamariensis with that of the congener Microhyla ornata from the western coast India and Sri Lanka and also compare the call properties of these two populations of M ornata to investigate intra-specific call variation. We find statistically significant differentiation in their acoustic repertoire in both cases,” the paper said.

Robin Suyesh, assistant professor of environmental science at Venkateshwara College and lead researcher of the paper, said the latest study — focusing on vocalisation of the frog — further helps establish the fact that the species in Delhi is Microhyla nilphamariensis and not Microhyla ornata.

“The frog is not found anywhere, barring a few spots such as Asola or JNU. The Central Ridge was one of the locations where we were able to find them in large numbers, with 100 to 200 individuals recorded in the six-year period. Though it may seem a large number, it is not, given the period of time over which the study was carried out, and the fact that the frogs should have been much higher in number in the wild,” Suyesh said, adding that stating a seasonal, rain-fed water body was currently sustaining the frogs in Delhi.

Megha Srigyan, another researcher from the department of ecology and evolutionary biology at the University of California, said the vocal diversity in Microhylids across the Indian subcontinent may also be used to identify and assess the distribution of this species.

“A majority of our study population comes from a forest in Delhi, which suggests that there is a lot of scope to monitor biodiversity in urban settings,” she said.

Experts further said the presence of the frog is an indicator of a healthy ecosystem.

“More often than not, the value of wildlife in urban ecosystems is underestimated and hence understudied. Our study highlights the importance of amphibians in urban ecosystems, as not just as an indicator of its overall health, but also with respect to the value they provide for conducting large scale research studies,” said Ashish Thomas, assistant professor at the SGND Khalsa College, who also took part in the study.