Researchers say amphibians are not getting enough time to complete the breeding cycles, eggs drying out early
Erratic and deficit rainfall in monsoon 2023 in the Western Ghats have affected the breeding cycles of amphibians, according to scientists. Animals usually found abundantly in the region during the season have been absent, showed recent visits by researchers.
Coastal Karnataka in the Western Ghats has recorded a 13 per cent deficit in rainfall since June, according to the India Meteorological Department. Most parts of Kerala have also seen over 50 per cent of rainfall deficit this year.
Jithin Vijayan, research fellow at Bengaluru-based Nature Conservation Foundation recently visited the rock outcrops of Ratnagiri, in the northern Western Ghats.
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“We have carried out a study on amphibians and reptiles during the last monsoon. A striking difference compared to last year is the increased number of dried rock pools, which are very critical for many threatened and endemic amphibians in the region,” said Vijayan.
Rainfall results in the formation of temporary rock pools and replenishment of the permanent water bodies where frogs breed, he explained. “The temporary pools require water to last for a few days depending on species’ larval period to enable frogs to breed and give birth to the newer generation,” Vijayan said.
However, in the northern Western Ghats, water remains in some pools for only two to three days under short-duration rainfall. Frogs lay eggs in this period but they dessicate or dry up before the tadpoles metamorphose into adults, as the pools lose water and moisture essential to complete the breeding cycle.
The details of Vijayan’s last visit are not comprehensive and the absence of the amphibians was not the focus of that specific study.
“Usually on average, in a square kilometre area, we can find around 1,000 pools. At least one third of these pools have dried this year. But these are very crude estimates and need to be studied in detail,” Vijayan told Down To Earth.
Primary streams in Coorg (Kodagu), Karnataka seem to be drying too, Madhushri Mudke found after a recent visit earlier this year. Mudke is a PhD candidate at Ashoka Trust for Research in Ecology and the Environment and Zoological Society of Landon’s EDGE Fellow.
“The frogs don’t seem to be breeding for as long as they used to. August rainfall in Coorg this year was less than expected. The flow in primary streams, which the amphibians heavily depend on for breeding and releasing eggs, is low,” she observed.
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Mudke found certain species of frogs to have completed one breeding cycle as some sub-adult frogs were seen. “The breeding process usually begins at the onset of monsoon and continues until November, which in some cases is disturbed, as it’s not raining that much,” she said.
“There is no study or data that can back the claim. Research in this direction is important to understand how climate change will impact these animals,” she added.
Species such as bull frogs, cricket frogs breed during the beginning of monsoon, while night and dancing frogs breed in late monsoons, Mudke explained. “With erratic rainfall, the breeding patterns are mixing and they are not getting enough time to complete the cycles,” she said.
The researcher has also noticed numbers of Malabar gliding frogs dwindling. “The Malabar gliding frogs were seen breeding abundantly about five years ago. Only a few pairs were found breeding and very few eggs were laid this year,”
These amphibians create nests on tree branches to lay eggs, but the dry and hot temperatures with humidity are dessicating them, she further said.
These eggs are laid over ponds or a waterbody so that when the tadpoles hatch, they fall in water and eventually develop into frogs. However, if the ponds dry up, these tadpoles die prematurely, Mudke explained.
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Herpatalogist and head scientist at Reliance Foundation, a non-profit, Varad Giri, said such erratic rainfall, which may become common in coming years, owing to climate crisis, will greatly impact the breeding patterns of frogs, especially the endemic ones.
“Certain species of frogs follow different strategies for breeding. Some species complete it in 2-3 days while others continue for 2-3 months. For example, Indirana species endemic to Western Ghats start breeding early. They lay eggs in moisture laden or damp conditions,” he explained.
The tadpoles feed on algae, which helps them develop and fully grow. But if the rains are erratic, algae does not form, depriving these tadpoles of their food for growth and development.
Another species Xanthophryne tigerina or the Amboli toad breeds only for two to three days in a year and lives in lateritic rock, commonly found in tropical regions.
“These frogs lay eggs in already water scarce areas. But the species have evolved and adapted themselves with the monsoons considering there will be continuous rains for months. But with erratic patterns, the rocks dry desiccating their eggs,” he said.
It also breeds only once a year. If the breeding is disturbed for consecutive years, the population will drop significantly, he noted.
Another factor to consider is that rock pools or water ponds where eggs develop need a certain ecosystem.
“Though temporary, these ponds have a certain pH level of water, have optimum temperatures, life-supporting oxygen and other parameters ideal for eggs to hatch and eventually for tadpoles to survive. If the rainfall stops for a long period, the water remains stagnant, changing all the above mentioned parameters,” he said.
Even a slight rise in temperature and polluting of water can impact the survival of these small creatures, Giri said.
Read more: World Rainforest Day: Goliath frogs need urgent conservation measures
Erratic rainfall, which is sudden and heavy, along with long breaks, is unsuitable for these species. “They require less but consistent rainfall over months to survive,” he said, adding a dearth of frogs may impact the population and survival dynamics of reptiles dependent on them for food.
Other than core habitat or Western Ghats, the amphibians are threatened in urban areas too, said Robin Panjikar, faculty assistant professor in department of environment science at SB College of Science and Technology, Delhi.
“Last year, Delhi received good rains owing to cyclones in May, but June and July were dry and didn’t rain as much. The tadpoles may have not survived with such short time rainfall. If the new recruitment each year gets affected, the amphibians will decline as they are already threatened with habitat loss,” he said.
Animals like birds and reptiles that prey on frogs will get affected directly if the life cycle of frogs gets disturbed. “Such food chain links will be broken in the long run,” he said.
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Researchers say fewer Malabar gliding frogs, an endemic species, were spotted in Western Ghats this year. Photo: iStock.png)
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