Are rock agamas adapting to city life? A study on sleep sites answers

Though humans have modified the South Indian rock agama's natural habitat, “they seem to cope well with the drastically altered conditions of city life,” says Dr. Mohanty.

Peninsular Rock Agamas preferred sleep sites that are rocky and warm. (Wikimedia Commons)

Where an animal chooses to sleep can be the difference between life and death in the wild. By studying peninsular rock agamas (Psammophilus dorsalis) in Bangalore city and surrounding rural areas, researchers have found remarkable behavioural flexibility in city agamas in response to the stressor of artificial light. The city dwellers were nine times more likely to use covered sleep sites that limit illumination, compared to lizards in rural areas.

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The team saw that both populations preferred sleep sites that are rocky and warm. “Sleeping animals are vulnerable to predators and even harsh climatic conditions. A suboptimal sleep site can, for example, be uncomfortably cold, especially for ectotherms (cold-blooded) like lizards,” says first author Nitya Prakash Mohanty from the Centre for Ecological Sciences, Indian Institute of Science, Bangalore. The findings were published last month in Behavioral Ecology and Sociobiology.

Delighted to share our work on sleep behaviour in urban vs rural lizard populations with some pretty cool findings (thread), out today in BEAS :) link: https://t.co/05565B40KM pic.twitter.com/TXuzmXzHlL

— Nitya Prakash Mohanty (@NityaPM) December 3, 2021

Why should we study where animals sleep?

Dr. Mohanty explains that examining sleep site characteristics in terms of structure (e.g., type of substrate, perch height), temperature profile (of the substrate in relation to other available but unused sleep sites), and light conditions can yield valuable insights into why animals choose specific sleep sites. “They tell us if the choice of sleep site is driven more by a certain ecological factor (predation) than others,” he adds.

‘Cope well with city life’

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Though humans have modified the South Indian rock agama’s natural habitat consisting of rocks and boulders to urban structures, “they seem to cope well with the drastically altered conditions of city life, via a slew of behavioural (as in this study) and physiological ways,” says Dr. Mohanty.

Previous studies from the research group have shown that lizards from urban areas learn faster to choose safe refuges during the day, can respond to higher stress better, and also show changes to their limb lengths that enable them to better use urban surfaces.

The team has now planned to quantitatively compare the sleep duration between rural and urban rock agamas, to see if sleep is hampered or of poorer quality in cities, despite behavioural modifications.

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“Broadly, we want to understand how sleep responds to a changing world and plan to evaluate sleep ecology (combining behaviour, physiology, and neurology) in response to urbanisation, biological invasions, and climate change,” concludes Dr. Mohanty.