IWN Daily Digest — Saturday, 17 October 2026
Young gharials appear to take their cue to start basking each morning from the light in the sky, a finding that raises questions about what artificial light along riverbanks does to a species with a recovery score of just 19 per cent.
As reported by Mongabay India:
“Like all crocodilians, Gangetic gharials regulate their body temperature using external heat sources. They warm their enormous bodies, which can grow to 15 to 20 feet in length, by basking on sandbanks, making it an important daily activity. Both temperature and light are important environmental cues for basking.”
Megha Khanduri, a postdoctoral researcher at the University of Helsinki in Finland, led the study, which followed 382 captive Gangetic gharials at the Deori EcoCentre in Madhya Pradesh. The animals had been raised from eggs collected at nesting sites in the National Chambal Sanctuary between 2021 and 2023, and the researchers divided them into 12 age groups.
Between 20 and 30 June 2023, the team ran morning and evening observation sessions for each group, counting basking animals and recording air and water temperatures along with the intensity of natural light. They also took head-region body temperatures of up to 10 gharials per group.
Light turned out to be the stronger cue for morning basking, especially among gharials under a year old. Those youngsters responded to lower light levels and left the water earlier, even on mornings when the air was colder than the water. The study found no link between light or temperature and evening basking.
The authors say light pollution could disrupt basking timing, which risks hypothermia and exposure to predators. They suggest captive enclosures should give the animals access to direct sunlight, since heaters and lamps alone may not do the job.
Expert Caution
Jailabdeen A, Project Director of the Gharial Ecology Project at the Madras Crocodile Bank Trust, raised several concerns about the design. Head temperature may not reflect body temperature because the head heats faster than the torso, June observations may not reflect winter behaviour, and a 10-day window is too short to capture seasonal patterns.
He also told Mongabay India that sand mining, dams, barrages and river interlinking are more urgent threats to gharials than light pollution, which he believes wild gharials largely avoid.
Khanduri’s earlier work found a threefold increase in night-time radiance along the Chambal and other gharial river systems between 2012 and 2020. A separate 2022 study found that the dark night sky area in Hastinapur Wildlife Sanctuary fell from 92 per cent to 67 per cent between 2015 and 2021.
Sources: Mongabay India
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