To Abhijit Das, scientist at the Wildlife Institute of India (WII), it sounded like a frog calling from underground. He and his team began searching beneath the thick layer of leaves covering the forest floor. “We are exactly on the call. But when we start moving the leaf litter, we don’t find it,” said Das. “The frog stops calling.”
A year later, two of Das’ students, N.V. Rajiv and Sourav Dutta, lay on the ground deep within the rainforest, slowly picking up one leaf at a time as they followed the frog’s distinctive sound. Finally, they spotted the calling male hidden in a depression in the mud under leaf litter. The team would later describe this as a new species of fanged frog, Limnonectes motijheel, in their paper published in Zootaxa in April 2026.
Detailed morphological and genetic analysis of specimens collected during surveys showed that this small, brown frog belongs to the Limnonectes genus, a group of fanged frogs whose males possess tooth-like projections on their lower jaw, giving them their name.
“This is the first species in our country that makes a cup-shaped nest on the ground completely under leaf litter which is many layers thick,” said Das, the study’s corresponding author. In some cases, they found leaf covers more than 10 to 12 leaves thick. This discovery opens up a “new research dimension” to understand the functional diversity of species, he said, adding, “Now that the species has been discovered, we need to know what function it is playing in the ecosystem.”
A complex group of frogs
There are currently 104 known species of fanged frogs of the Limnonectes genus distributed across South, Southeast and East Asia, the study noted. According to Das, strong competition exists among males of this group, who use their ‘fangs’ to fight other males, possibly for a mate. This may explain why male fanged frogs are larger than females, unlike in most other frog species.
Although L. motijheel is currently known from Namdapha Tiger Reserve, researchers suggest it may also be found in neighbouring Dehing Patkai National Park, Assam. “The habitat is similar to Namdapha,” said Bitupan Boruah, a Ph.D. student at WII and the study’s lead author.
The team named this ground-dwelling frog after Motijheel — a small, biodiverse wetland within the protected area where they recorded several individuals. Motijheel serves as breeding ground for at least 10 amphibian species, the authors noted.
Between May 2022 and June 2023, researchers collected six specimens while surveying the evergreen forests for herpetofauna during the pre-monsoon months, when amphibians are most active. The species was first detected through its call, which the team was only able to record during their fourth sampling survey in May 2023. Boruah explained they use a red light in the process to avoid disturbing the frog and obtain its natural call.
Back at the lab, researchers extracted the frog’s tissue samples for genetic analysis, comparing its DNA with all available genetic sequences to ensure this specimen is distinct from related species. They also compared the frog’s physical characteristics and the properties of its call with related species, confirming L. motijheel is a new species using three lines of evidence.
Their analysis showed that L. motijheel is one of several species comprising the L. limborgi species complex — a group of closely-related species that look similar but are genetically distinct. L. limborgiwas once considered widely distributed. But in 2021, researchers found nine distinct lineages within this group. Of these, only three — including L. motijheel — have been formally described so far.
“It is good that their taxonomy is resolved,” said Gururaja K.V., batrachologist and professor at Srishti Manipal Institute of Art Design and Technology, MAHE. “Kohler et al, in 2021, indicated there is such a group and now authors got proper morphological and genetic data to ascertain it as a new species,” added Gururaja, who was not associated with the study.
The team also recorded the presence of another fanged frog, Limnonectes longchuanensis, the first record of it in India. Previously reported from China and Myanmar, this species is larger and breeds in puddles along the forest trail.
The two new records bring the number of fanged frog species in India to six. Five of these are found in northeast India, south of the Brahmaputra River which, the authors suggest, acts as a geographical barrier, restricting species’ distribution.
Specialised breeding habitat
Mud-nesting has been observed in other species as well. Nidirana noadihing, described in 2023 from the same forest, creates an open mud pit too, though without the leaf litter cover that is unique to L. motijheel. The mud nest plays an important role in its breeding, said Das. But the details of this specialised reproductive behaviour, like much else about this frog, remain a mystery for now.
Researchers hypothesise that males call for mates while hidden in their nest, which transforms into a “private pool” when it rains. Females may lay their eggs in this pit that hatch into tadpoles while remaining hidden under leaf litter, far from waterbodies where predators lurk. “So it gives a two-way protection,” Das added.
They further speculate that a parent carries these tadpoles to a water source where they develop into adult frogs. Similar behaviour has been observed in related species — L. palavanensis and L. finchi in Borneo — where the male carries the tadpoles on its back to a waterbody. The team hopes to investigate this further in the case of L. motijheel. “We strongly presume that very strong parental care probably exists within this species of frog,” said Das.
Having discovered what he calls a “unique breeding habitat”, he emphasised the need to monitor the frog’s breeding biology, behaviour and acoustic properties in the future, cautioning that their findings are preliminary at present.
Monitoring amphibian diversity
This discovery is significant given how little is known about amphibian diversity and the inadequate conservation attention this group receives, despite being the world’s most threatened vertebrate class. “It’s possible that without knowing a frog, they are going extinct,” Boruah said.
The study also emphasised the rich biodiversity of Namdapha Tiger Reserve, much of which remains undocumented. In the last five years, Das and his team have recorded around 15 new-to-science species by only exploring the lower elevation band of this protected area. “Areas that are beyond 2000-metre elevation are completely unexplored,” he added.
“As the authors rightly say, there needs to be extensive survey in Namdapha to understand biodiversity, specifically amphibians,” agreed Gururaja.
The discovery of L. motijheel also highlights the importance of bioacoustics for conservation research. Das recommended carrying out regular monitoring of aquatic diversity in protected areas by recording soundscapes of overlooked microhabitats such as canopies or the forest floor, developing call libraries and training forest staff. “Once we know the call of all the species, that opens up a great dimension for citizen science approach in wildlife monitoring,” he added.
(The article was first published in Mongabay India)
