Remarkable Rodents: The Fighting-Fit Super Mammals

We were stumped.

This was day 4 of us trying to figure out what was stealing my dog’s poop from our fourth-floor balcony in an apartment roughly 60 feet up from the ground. The only urban creatures we thought could get up there were birds.

But no bird could move or stash poop the way we found it — neatly hidden in little sheltered corners of the balcony where it gave off gouts of noxious smells. This type of hoarding behaviour was very typical of rodents, but the only rodents that could get up to our balcony were squirrels, and they weren’t exactly known to feast on dog poop.

So, how was a rodent capable of doing this getting up to our balcony?

We eventually figured it out. Using a jury-rigged camera trap with a car dashboard camera, selfie stick, and several wires, we saw a house rat wriggling its way up the outside wall of the balcony and sliding through the gaps in the pigeon net. The rat scooted under and behind a cabinet, quickly sniffed the doggy potty pad from its hiding place and scurried out of the balcony. It was over in about three seconds, and if we’d blinked, we’d have missed the activity.

While we searched for the most humane methods to rid ourselves of this unwelcome visitor, it struck me that rodents — especially those that live around humans — are ridiculously clever and fascinating.

Rodents in urban spaces

India is home to about 128 species of rodents. However, not all can thrive in or even tolerate the urban concrete jungles of cities. One study in Bangalore found that rodents form a large percentage of the many small mammals living within and on the outskirts of cities.

In large Indian cities, we find seven common species of rodents, namely, the northern and southern Indian palm squirrels (Funambulus pennanti and Funambulus palmarum, respectively), house or black rat (Rattus rattus), Wroughton’s or brown rat (Rattus norvegicus), house mouse (Mus musculus), and the bandicoot rats (Bandicota bengalensis and Bandicota indica, respectively). Besides these, one rodent-like mammal, the Asian house shrew (Suncus murinus), also deserves a special mention as they are often mistaken for mice, although they have much longer snouts than mice.

Shrews usually do not prefer to enter buildings and are mostly found in and around urban green spaces and garbage dumps. Also known as “chuchunda/chuchundri”’ in Hindi and “sundeli” in Tamil, these little creatures are voracious insectivores and one of the most beneficial small city mammals to humans as they help keep cockroach populations under control. However, they are usually unwelcome visitors due to their stinky body odour (that serves to keep away predators). One of the most fascinating things about shrews is that mothers lead their babies around in a shrew conga. Since they are almost blind, one baby holds on to the mother’s tail with its mouth, while each successive baby holds on to the previous one’s tail. As journalist Janaki Lenin puts it, “the public image of these poor creatures needs an overhaul”.

The only urban rodent that shares the shrews’ general reluctance to invade human buildings is the squirrel. In Indian cities, squirrels are welcome visitors in gardens and balconies due to their entertaining antics and their association with Lord Rama in Hindu mythology. Unfortunately, they can sometimes create havoc by nesting in houses and chewing on wires.

The black rat, Wroughton’s/brown rat, bandicoot rats, and the house mouse are, unlike squirrels and shrews, more than ready to take up residence inside human dwellings and warehouses if given the chance. The black, brown, and bandicoot rats are aggressive burrowers and are even known to burrow under concrete. Black and brown rats and house mice are agile climbers and often nest in the roofs of houses.

The brown rat was once a warehouse pest in coastal cities such as Mumbai and Kolkata but is now found all over India, especially in sewage systems. The black rats, also known as ship rats, have colonised six continents and most of the world’s islands by stowing aboard ships. Ships were often home to huge colonies of black rats, with some of these rats spending their entire lives on ships, establishing core populations that would bleed off members at every port of call. Genetic studies show that European ships carried black rats from Asia to other parts of the world, causing “waves” of black rat invasions.

Given how resourceful and clever rats can be, it’s no wonder that the brown rat was the first mammal domesticated for research. Today, these rats have been bred into thousands of strains and are the cornerstones for behaviour, neurobiology, drug testing, and immunology experiments.

How do rodents in cities differ from their rural/wild counterparts?

A 2020 study comparing the genetics of the brown rat population of New York with one in Central China (its “presumed” ancestral range) shows huge differences between the two. The most changes between these two populations seem to have occurred in the genes associated with diet, behaviour, and movement. The study also suggests that these changes may help urban rats survive better in urban conditions. Even more surprising, though, is the result that urban humans and rats seem to be developing similar genetic changes. Since urban rats are so closely associated with humans, the shared stresses, diets, and exposure to pathogens could lead to this trend where humans and rats follow similar evolutionary paths and undergo similar changes.

But it’s not just urban rats that differ from their rural/wild counterparts. Urban red squirrels in Europe are less stressed by new environments but bolder and more aggressive towards humans than their rural counterparts. Other studies on mice suggest that urban mice are better problem solvers, more tolerant towards one another, bolder, and more explorative than rural/wild mice.

Overall, it’s clear that close association with humans is changing how rodents evolve, which in turn is also affecting humans — so much so that rat expansions have been used to understand how humans migrated, formed settlements, and established trade networks. 

Rodents as pests — can we ever be neutral neighbours?

Despite their close associations with humans, rodents aren’t always our friends. Rodents in India are carriers of several deadly diseases, including the Hantavirus that causes haemorrhagic fever, leptospirosis, Kyasanur forest disease, and the dreaded plague. India’s tryst with plague began in 1896 in Mumbai and terrorised the nation for almost 20 years. But although plague has remerged in small pockets of India over the last six decades, these outbreaks have been relatively small and well-contained. Apart from transmitting diseases, rodents also cause huge economic losses in damage to materials, structures, and food. According to a report in 1975, food-short India at that time lost an estimated 10 per cent of its food grains to rodents.

However, changes in food grain storage practices — some as simple as storing grains in metal boxes instead of jute sacks — have helped save more than 4 million tonnes of food from rodent and other damage over the last decade. In addition, ecologically based rodent management strategies have been formulated. These integrate good agricultural practices (such as rodent-proof storage of grains) with careful management of natural resources (such as installing perches and nest boxes to attract raptors that prey on rodents). This multi-stakeholder system (involving farmers, scientists, NGOs, and government institutions) has been successful in some rural settings. The strategies work by controlling the rodents’ access to food and shelter, reducing migration, and using natural predators to bring down rodent populations.

These simple rules can apply to both rural and urban settings but will require some basic changes in our behaviour, such as proper garbage disposal and educating the public about rodent behaviour. This will also need to go hand-in-hand with scientific pest management that integrates an understanding of rodent behaviour with effective and humane ways of extermination.

Circling back to my balcony story, my unwanted rodent guest thankfully never returned after we caught it on camera. And I mean that with all my heart, as the rodent capture and kill devices I found available in the market were uniformly ghastly.

Photo sources: brown rat, brown rat swimming, lesser bandicoot rat, greater bandicoot rat, house mouse, house shrew