Nandini Rajamani, a faculty leading the Sciurid Lab at the Indian Institute of Science Education and Research (IISER), Tirupati, speaks about her group’s research studying palm squirrels, which reveals that cities are evolutionary arenas shaping the traits of animals living within them.
India is home to a remarkable diversity of squirrels, including the familiar tree squirrels, the more cryptic nocturnal flying squirrels, and ground squirrels that are only found in the high reaches of the Himalaya. The group of small palm squirrels—tree squirrels in the genus Funambulus—is especially familiar to people in peninsular India. With their striped backs and distinctive chik-chik calls, they are a part of the everyday soundscape in rural and urban areas. For many of us, these small, agile funambulists are ubiquitous companions—nesting under the tiled roofs of traditional houses, or finding shelter in the exhaust fan vents or air-conditioning units of high-rise apartments. This association of palm squirrels with human habitation is a long-standing one, even finding mention in the ancient Tamil text, the Thirukkural, dated around 2000 years ago. Despite these associations, scientific studies of how palm squirrels navigate today’s rapidly changing landscapes are still in their early stages.
At the Sciurid Lab at IISER Tirupati, we focus on understanding the evolution of palm squirrels, their behavioural responses to change, and their adaptations to life in modern environments. One of our central questions is whether squirrels thrive in cities because urban conditions favour higher densities, or whether their populations are naturally high in all ecosystems.
Palm squirrels are a genus of seven species distributed in South Asia, including India and Sri Lanka. These are small, mouse-sized squirrels that are brown to grey in colour with patterns of stripes on their backs that vary across species. Four species occur in India, while three are found in Sri Lanka. The three-striped palm squirrel, Funambulus palmarum, found in the drier eastern parts of southern India and in Sri Lanka, and is a highly commensal species. We set out to ask whether this species thrives in cities because urban conditions favour higher densities, or whether their populations are uniform across forests, villages, and cities.
To explore this, we conducted a two-year study across a landscape gradient stretching from forests to urban centres around Tirupati, a rapidly growing town in Andhra Pradesh. We had teams of people counting squirrels and characterising their microhabitats in relation to human presence. The results were striking, and we found that squirrel density and abundance increased significantly with urbanisation. However, this came with a caveat—squirrels seemed to occur mostly in areas with specific types of trees, especially commonly planted fruiting and flowering trees in gardens and along roadsides. These include the familiar but often non-native Neem, Prosopis, Pongamia, and Copper pod, among others. We saw similar patterns on the Kodaikanal plateau of the Western Ghats, where the three-striped palm squirrel occurred in high numbers in villages, especially around gardens with planted fruiting and flowering trees.
Living in close quarters with humans seems to change other aspects of squirrel behaviour as well. Urban squirrels were noticeably bolder than those in less disturbed habitats. In a carefully designed food experiment across the forest-to-urban gradient, we offered squirrels both familiar and novel food items, including processed human foods. Urban squirrels approached novel foods more quickly, consumed greater amounts of processed items, and even showed a preference for high-fat foods. In contrast, rural squirrels were more cautious and selective. We also saw this same preference for fatty foods in an observational study around Tirupati, where we measured nutritional content of foods eaten by squirrels - urban squirrels would gravitate to fat-rich foods (like chips and payasam) in garbage dumps. There was also more social interaction between squirrels in urban areas, and shyer animals would follow bolder individuals that were exploring new food items. Our findings so far suggest that the urban lifestyle not only shifts their dietary choices and risk-taking behaviours, but possibly also their social interactions.
What does this tell us more broadly? First, it highlights the remarkable flexibility of some palm squirrel species in adapting to human-dominated landscapes; a pattern that is seen in many species the world over. Commonly denoted as ‘Urban Adapters’, these adaptable species might have traits like boldness, sociability, and a willingness to experiment with new foods which may be key to their success in foreign habitats. Second, it emphasises that urban environments are evolutionary arenas. Just as humans are reshaping landscapes, cities are reshaping the animals that live within them.
Other Sciurids by Aparajita Datta and Nandini Rajamini in Mammals of South Asia (Volume 2), edited by AJT Johnsingh and Nima Manjrekar, Universities Press, Hyderabad, 2015.
