How does artificial light at night affect common toads?

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Artificial light at night (ALAN) is a global phenomenon. By changing the light–dark cycle, it may directly affect many organisms’ physiology and behaviour, including daily rhythms, hormonal regulation, food intake, metabolism, migration and reproduction. Although ALAN is known to strongly influence the health of humans and laboratory animals, wildlife studies remain scarce. Amphibians are among the most nocturnal vertebrates and have an unfavourable conservation status in most parts of the world.

To investigate ALAN’s consequences, researchers experimentally exposed 36 adult breeding male common toads (Bufo bufo) to light intensities of 0.1, 5 or 20 lux for 20 days. They studied activity using infrared cameras, whole-body oxygen consumption using respirometry, and also measured body mass and food intake.

Over 24 hours, ALAN reduced toad activity by 56% at 5 lux and 73% at 20 lux. Total energy expenditure was unaffected, but energy allocation changed. Standard energy expenditure increased by 28% at 5 lux and 58% at 20 lux, while activity energy expenditure decreased by 18% and 38%, respectively. Body mass and food intake were unaffected.

The study suggests that ALAN has a major role in common toad activity and energy metabolism, potentially affecting the fitness of common toad populations negatively over the long term. The authors say generalizing these results to other taxa is crucial for biodiversity conservation in an increasingly light world.