Warning Of Climate Change or Anthropogenic Pressure: Mass Mortality Of Toads At Perbing Lake, South Sikkim

Dr BASUNDHARA CHETTRI Assistant Professor Department of Zoology Sikkim University Ms RABINAMOTHEY R

Amphibians: the most vulnerable vertebrates

Amphibians are the first vertebrates that attempted life outside water. They were largely successful in conquering land except for breeding. Hence, their life cycle is completed in both terrestrial and aquaticsystem and that’s how the term “amphibians” (referring to animals that lives both in water and land) is derived. Amphibians have a dual life history,land-dwelling adults gather at ponds or streams in spring to meet, mate and reproduce. Females lay eggs in water, which are then fertilised by males (external fertilization). Larvae (tadpoles in case of amphibians) which hatch out from eggs,developand metamorphose into tiny froglets andthen return to land thus completing their life cycle.

Amphibians are highly vulnerable to environmental changes because of their moist skin and life history traits. The causes for amphibian declines are many and complex including habitat destruction, pollution,introduction of exotic species, diseases and climate change. Among these, a harmful chytrid fungus called Batrachochytrium dendrobatidis (Bd) is causing major declineof amphibians worldwide. It leads to a disease known as Chytridiomycosis, which affects the skin of frogs and other amphibians. Since amphibians breathe and absorb water also through their skin, the body infection disturbs their balance and can lead to death. This disease has caused mass mortalityof amphibians in regions like Costa Rica, Panama, and Australia.The Golden Toad (Inciliusperiglenesoriginally described as Bufo periglenes), once found abundantly in the Monteverde cloud forests of Costa Rica, is one of the most well-known examples of recent extinction due to climate change. First described in 1966, thistoad was last seen in 1989 and was declared extinct in 2004 by the International Union for Conservation of Natureand Natural Resources (IUCN). Within a short span of 23 years after itdescription, it became extinct from the world. It said that if chytridiomycosis is a bullet then the trigger of gunwas pulled byclimate changethus resulting in the extinction of golden toad from the world. Warming temperature and changing rainfall patterns provided the ideal condition for the fungus to proliferate rapidly,followedby consecutive two to three years of droughts in Monteverde, Costa Rica in the late 1980s, lead to the extinction of golden toad. Today, the extinction of the golden toad is seen as a strong warning sign of global amphibian decline, showing how anthropogenic activities, climate change and infectious diseases together can threaten biodiversity in a short span of time.

A recent case fromPerbing

Perbing is a small villagein the Namchi district of Sikkim, Indiacharacterized by community driven organic farming practices. The village is demographically dominated by the Sherpa tribe of Sikkim who largely depends on agriculture for their livelihood and produce seasonal vegetables such as potatoes, radish, carrot, cauliflower, cabbage, peas, coriander, and exotic fruits such as kiwi. The temperate forest found in the area is dominated by oaks, pines and rhododendrons. The village experiences a temperate climate with high humidity making a favourable habitat for various flora and fauna including many amphibian species such Duttaphrynushimalayanus, Megophyrsrobusta, Amolopsmontiocola, Roarchestusannandalietc.

Along with rich diversity of flora and fauna, Perbingis blessed witha sacred lakein the middle of the forest. The pond is non-perennial and gets filled up during monsoon season and dries during winter.The lake isa breeding ground for many frogs and toads during monsoon season.However, recently this pond was beautified for the sake of tourism using cement and other materials for concretization.Such unthoughtful anthropogenic activity in the pond restricted breeding activities as these frogs and toads lay their eggs in crevices between the boulders surrounding the lake. On 12^th March 2026, a video on social media was posted regarding a mass death of toads (Duttaphrynushimalayanus) locally called “Bhaguta” from Perbing lake. Considering this, a team from Department of Zoology, Sikkim University visited the site on 17^th March 2026. Upon our visit, we found 42 pairs in amplexus (mating pairs), all females (larger one in the picture below) dead, whereas four males were alive. Additionally, six dead females and 12 spoiled egg clusters were noted around the lake vicinity. Additionally, we also noted 23 individuals which were alive but inactive. During our second visit on 3^rd April, we encountered three solitary dead individuals and 14 spoiled egg clusters whileno live individuals were observed. On our third visit on11^th April, we encountered only one dead individual and no live individuals.

Image 3:Duttaphrynushimalayanus,from left to right:  Spoiled egg clusters,dead female, Amplexus (female dead, male alive)

While the actual cause of death of toads atPerbing lake is yet to be known, we have collected skin swabs and sent it to the Centre for Cellular and Molecular Biology (CCMB), Hyderabad to rule out the possibility of chytrid fungus. However, the death of females much higher than males compel us to look further and investigate the cause of mass mortality. It can be speculated that gravid (with eggs inside) females being heavier and larger suffered more from dehydration and heat from the concrete floor while male suffered less as they were rested upon females. However, more investigation is needed for clearer understanding of the situation.

In addition to the toad species, pond ecosystems support a diverse assemblage of organisms, including zooplankton, microplankton, and phytoplankton, which are integral to trophic dynamics and ecosystem functioning. A significant proportion of these taxa remain undocumented and their role in nutrient cycling, organic matter decomposition, and overall ecosystem stability is yet to be understood. However, many developmental interventions may be hazardous for the local biodiversity as they may disrupt the normal activities of these organisms. Hence, prior to initiating any infrastructural developmental activities, it is imperative to conduct comprehensive baseline assessments of the aquatic system, including physicochemical water quality analysis, detailed characterization of benthic structure and composition, and associated flora and fauna.Such planned initiatives will not only be beneficial for the flora and fauna but it also aligns with Sustainable Development Goals (SDGs). Any development must be supported by the three foundational pillars—social, economic, and environment. Social and economic developments are an integral component of human civilizations whilethe ignorance to environmental dimension may doom the very existence of human being in this earth.