Light cues outweigh temperature in prompting captive gharials to bask early

Light cues dominate morning basking decisions of captive Gangetic gharials, a new study finds.

What Happened

Researchers observed 382 gharials raised from eggs collected 2021‑2023 and housed at the Deori EcoCentre in Madhya Pradesh. From 20‑30 June 2023 they recorded basking numbers in three one‑hour morning and evening sessions, measuring air and water surface temperatures, natural light intensity and head‑region body temperature of up to ten individuals per group. The youngest gharials, less than one year old, left the water earlier than older ones, responding to lower light levels even when the air was colder than the water.

Reaction

Lead author Megha Khanduri, a post‑doctoral researcher at the University of Helsinki, says this shows light is a stronger cue than temperature for morning basking and warns that artificial night lighting could cause premature basking, risking hypothermia or exposure of hatchlings to land predators. The study also noted a three‑fold rise in night‑time radiance along the Chambal basin between 2012 and 2020, and a drop in dark‑sky cover from 92 % to 67 % in Hastinapur Sanctuary (2015‑2021). Jailabdeen A, project director of the Gharial Ecology Project at the Madras Crocodile Bank Trust, raised concerns about measuring head temperature instead of torso temperature and the limited June‑only observation period, urging longer seasonal studies. He added that while protected areas keep gharials away from bright zones, sand mining, dams and river changes remain the most urgent dangers.

Context

Light pollution has risen across many Indian rivers, making dark habitats scarcer. Gharials prefer dim riverbanks and may avoid bright spots, but limited dark zones can affect their natural behavior. Understanding how artificial light alters basking helps guide both captive care and river‑bank management.