Imagine you are a Crested Serpent Eagle and can fly in and out of Bengaluru city, unperturbed by the traffic to slow you down. You are gliding above the rocky landscapes near Nandi Hills. With razor-sharp eyes, you notice a foot-long, black-yellow male lizard perched on a rock. He is changing his colour to orange-black and doing push-ups to attract a not-so-colourful, cryptic female lizard. You wonder if you should grab this lizard for a meal but decide you are not that hungry. Later, as you get closer to the city, you notice things are changing – rocky areas are fast disappearing and giving rise to more buildings. You pinch yourself for not being proactive and picking that meal earlier. But then you notice, right there on a wall fence that separates two houses, a black-yellow lizard doing push-ups!
Let’s now return from being an eagle in the sky to a human being on the ground – someone who can take all these bits and pieces of information about lizard presences, absences, and various environmental conditions, to make sense of where the insect-eating Peninsular Rock Agama (Psammophilus dorsalis) lives in the city. That’s the study a bunch of us led by Dr. Maria Thaker from the Centre for Ecological Sciences, Indian Institute of Science, Karnataka, carried out.
We started by investigating how the city of Bengaluru changes as one moves away from the city’s centre (which is the Government Post Office near Cubbon Park). The most obvious change, of course, is that built-up areas reduce drastically 20 km away from the city centre and give rise to croplands and plantations. Artificial light at night is linked with built-up areas, and so, follows the same trend – night light intensity is high close to the city centre and then declines as you move away. What about temperature? Is the city a hot island with the peripheral areas being cooler? Actually, it is quite the opposite – the inner areas of the city experience milder temperatures than the outskirts. And finally, what about lizards’ avian predators (like the Crested Serpent Eagle) – do they differ within and outside the city? Not so much: some raptors like Black Kites do take to cities. All this indicates that the environmental conditions a lizard experiences in the city are bound to be quite variable and dependent on where they are found.
We then sampled where the Peninsular Rock Agama are found across the city. The sampling began from the city centre and went as far as 60 km away, reaching close to Kolar on one side and Ramanagara on the other. We counted lizards in many 20 x 20m plots and collected fine-scale habitat information that is not available from satellite data, using photographs taken by drones. Taking this information about lizards’ presence and the environmental conditions they experience, at the finer spatial scale we found that the lizards are most likely to be found in places with rocks, and at a larger landscape scale, the lizards are likely to be found in places with higher temperatures.
Other environmental conditions we examined to understand the lizard’s presence in the city were how rocky landscapes changed over the last decade, and how connected these rocky areas were to each other. But both these conditions did not turn out to be that important. These results, however, should be interpreted with caution – land use change over, say, twenty-five years might be more significant to the lizard population than the last ten years that we examined. Similarly, the connectivity of rocky areas was assessed at a large scale (1 x 1 km), but finer scale connectivity might matter more to the lizard. Take the example of a rocky patch found in the middle of Bengaluru in Lalbagh Botanical Garden, where the lizard was not recorded during the lizard survey. Their absence could mean that the lizards are not at all there in the patch, or their numbers are so low that it is difficult to detect them. This rocky patch is surrounded by greenery, and then buildings all around – it is hard to imagine how a lizard could enter and settle down in this patch after navigating across so many barriers.
Does this mean that all the other conditions, like the amount of built-up areas or night light intensity, do not affect where the lizards are found? The rock agama’s presence in the city does suggest that it can persist in pockets, with flexible behavioural changes irrespective of the challenges and conditions they face from rapid urbanization. For example, the conditions the lizard experiences at its refuge site at night are similar, irrespective of whether the refuge is a natural rock crevice or a wall crevice in the city. The city lizards are also fast learners of where their refuges are, which might help them escape predators like the Crested Serpent Eagle or feral dogs.
But to what extent of urbanization can the lizards tolerate? Can they survive a decline in insects — their primary food resource – or will that be the deal breaker? It is hard to say. Ideally, if one could monitor lizard numbers for many years continuously across the city, then one could, with greater confidence, say if the lizard is doing okay, and what change is affecting its survival. However, such long-term monitoring studies are difficult to carry out – for starters, imagine surveying the city of Bengaluru for lizards year after year. But until then, protecting some of the rock agama’s native, rocky landscapes from rampant mining and restoring destroyed habitats might be key to the lizard’s conservation. Given all these battles the lizard is fighting, you are probably lucky if you live in a part of the city that hosts this guy who basks on your wall, does push-ups, and changes his colour to attract mates.
Acknowledgement: I thank Sheshadri KS and Maria Thaker for their input on the article.
For more information on the study, check our publication in ‘Frontiers in Conservation Science’. Do also check other publications on the Peninsular Rock Agama from Dr. Maria Thaker’s lab.
- Thaker M, Amdekar MS, Mohanty NP, Nageshkumar AK, Prakash H and Seshadri KS (2022). An expanding cityscape and its multi-scale effects on lizard distribution. Front. Conserv. Sci. 3:839836. https://doi.org/10.3389/fcosc.2022.839836
- Mohanty NP, Joshi M and Thaker M (2021). Urban lizards use sleep sites that mirror the structural, thermal, and light properties of natural sites. Behav Ecol Sociobiol 75, 166. https://doi.org/10.1007/s00265-021-03101-5
- Batabyal A, and Thaker M (2019). Lizards from suburban areas learn faster to stay safe. Biol. Lett.152019000920190009. https://doi.org/10.1098/rsbl.2019.0009