In teeming city, lizards selective in choosing snoozing sites

In the hustle-bustle of a teeming metropolis, it may seem inconceivable that small wild animals such as reptiles can sleep restfully.

But a team of scientists who spent months poking around urban neighborhoods at night has found that at least one species of lizard is getting around the hurdle of insomnia by picking out urban snoozing spots which closely resemble their rural counterparts.

Sleep is fundamental for animals. Sleep helps the brain to sort and categorise memories while restoring energy. However, urban habitats like cities with their higher ambient temperatures, artificial structures like walls and buildings, and artificial lights at night, disrupt an animal’s sleep quality and patterns.

To adapt to these unusual conditions, urban peninsular rock agama has been choosing sleep sites that have the same type of surface, plus the amount of light and heat received as rural locations, according to researchers from the Centre for Ecological Sciences (CES) at the Indian Institute of Science (IISc) in a new study published in Behavioral Ecology and Sociobiology.

While scientists have a reasonably good understanding of how animal brains work during sleep, Maria Thaker, Associate Professor at CES and senior author of the study, said how these creatures sleep in the real world is less well known.

“We know from human literature that certain conditions allow us to sleep better than others, and some disrupt our sleep. But animals live in the real world with all these conditions … and we wanted to understand where and how they sleep in the wild,” she said.

The researchers compared lizard sleep sites in urban and rural habitats to look for differences in the types of surfaces the lizards were sleeping on: the extent of cover, temperature and amount of light received.

“In rural areas that are undisturbed, we scanned rocks, boulders, the ground, and shrubs to look for sleeping lizards. But in (urban) Bangalore, we would go into people’s backyards, because these lizards occupy empty lots or undeveloped plots, where there would be some concrete blocks that they use,” says Nitya Mohanty, first author of the study.

However, prowling around nocturnal neighborhoods with headlights and fancy camera equipment, led the team to begin drawing attention from the public and the police. They had to often explain what they were doing, according to the researchers.

Since urban habitats pose differences in terms of structure and more illumination at night as compared to rural areas, lizards would have to cope somehow, Thaker pointed out. “One way is to just sleep under these conditions. Or they can cope in another way: by finding conditions that closely match the wild as much as possible. What we found is somewhere in-between the two,” she said.

The lizards were found to pick structures that mimicked those in their natural habitat – such as rough concrete blocks that resembled their rocky sleep sites in the wild. Temperatures of both urban and rural sleep sites were also found to be similar.

Urban sleep sites, however, were nine times more likely to be sheltered and covered as compared to rural sites, and this helped address the problem of artificial light. This indicates that the lizards try to mitigate urban stressors by being flexible in their sleep site choices, and end up picking sites that resemble their rural sites.

Studying animals coping with anthropogenic environments is very important, according to Thaker. “The world is changing, and it is going to continue to change. So, if we know what it is that (other organisms) require to live here, then we can make some choices of our own to help keep them here.”

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