Contributions of IIT Bombay researcher to the field that won the 2023 Nobel Prize in Physics

Captive big cats show stress in different ways

August 21,2017
Read time: 6 mins

Photo : Vignesh Kamath / Research Matters


Observing wild animals in zoos is a refreshing break from everyday monotony for most of us. For the zoo animals, on the other hand, it’s a stressful life. Animals in zoos show certain specific behaviours not seen in their wild counterparts: elephants sway their heads from side to side, chimps rock back and forth, bears bite their feet, giraffes lick walls, and leopards pace in their cages, to name a few. Known as ‘stereotypy’, these behaviours are coping responses commonly observed in captive wild animals.

Being held behind bars – literally or figuratively – can be depressing for anyone. Wild animals, as such, are not evolved to exist in the zoo environments, and they tend to face a number of challenges in captivity, for which they are not equipped. The climatic conditions, the food provided, and the size and nature of captive habitat are very different from what exists in the wild or natural habitat.

Stereotypic behaviour is a repetitive pattern of action displayed by such animals, which have no obvious purpose; it is a sort of restlessness. Although not directly linked, stereotypy has been associated with factors related to captivity such as enclosure or cage size, social atmosphere with conspecific (their own species), human intervention, etc. The behaviour, therefore, suggests that the animals perform such actions when they are stressed or have been habituatedat the present, from a stressful event in the past.

Prof. Nagarajan Baskaran, and his team from A.V.C. College in Tamil Nadu, studied stereotypic behaviour in tigers and leopards, to test whether stereotypy and stress were correlated. “The idea was that if an animal is showing stereotypic behaviour (a psychological stress) then it is stressed and therefore the stress hormone levels (physiological stress) in the animal should be accordingly high. As what we expected our study, proved that this is true”, says Janice Vaz, the first author of the study.

Studying stress in animal subjects isn’t as easy as done with human subjects. This is especially so when it comes to wild animals. Researchers, therefore, measure Faecal Corticosterone Metabolite (FCM) levels to analyse the amount of stress the animal is dealing with. The theory is simple – when animals are stressed, their bodies produce more stress hormones, and a large amount of this is excreted in their faeces. And, obviously, obtaining faeces to measure hormone levels is far less complicated than drawing blood samples each time.

The group of researchers studied animals from 6 zoos, located in Pune, Thiruvananthapuram, Thrissur, Chennai, and Delhi. They monitored 41 Royal Bengal tigers and 21 Indian leopards for over a period of seven months, for stereotypic behaviour and the presence of stress hormones in their faeces. They even assessed environmental parameters such as the size of captive space, how closely the enclosure was made to resemble the wild habitat, temperature, number of visitors and even the zoo keepers' attitude towards the animal. Finally, they statistically analysed their observations, comparing stereotypic behaviour with hormone levels and habitation characteristics.

Of the 19 environmental and biological factors assessed, differences in stereotypic behaviours were only observed in enclosure size and keeper attitudein case of tigers and tree density in case of leopards – that is tigers in larger enclosures and with positive keeper attitude had significantly lowerstereotype than those maintained in smaller enclosures or with negative/neutral keepers, while the leopards managed in enclosures with higher tree density had significantly lower stereotype than those managed in enclosures with lower treedensity.

Similarly, among 19 factors tested, differences in FCM levels were observed only with health matters in the case of tigers — tigers with severe health problems had significantly more FCM than those with minor/without health problemsand in case of leopards, only inrelation to zoo keeper attitude — leopards cared for by active interested zoo keepers (who took their role seriously), had lower FCM levels than those supervised by keepers who didn’t care as much. Other factors such as the percentage of grass and tree cover, presence of stones and ponds, ambient temperature, etc., did not influence FCM levels but did contribute significantly to stereotypy.

These findings are comparable with the behaviour of tigers and leopards in the wild; i.e. tigers require larger natural habitats for fulfilling their needs, while leopards can manage even with smaller isolated patches but with dense vegetation cover.

Stereotypy is not completely understood, although there have been numerous attempts to study the behaviour in various species. What we do know is that stereotypy indicates a poor psychological state and that it is influenced by a number of factors, including being separated from mothers at early in life.

Prof.Baskaran who has been studying large mammals for over two decades, explains how stereotypy serves as a coping mechanism. “FCM levels are not always the best indicators of stress”, he says. “If an animal is continuously exposed to a certain form of stressful environment, which is beyond its ability to cope with, then the animal may begin to exhibit higher FCM levels. Thus, it is better to study the stereotypy as an indicator of stress because it reflects the animal’s first attempt to cope with the stress.”

Recalling an 11-month old leopard cub that she looked forward to visit during research, Janice observes “It was born in the zoo to parents who were caught from the wild. The mother passed away and the father was maintained in another cage next to it, allowing no interaction with the cub. It was expected that the cub would display wild behaviour. But at eleven months, the cub was already showing stereotypic behaviour although it did exhibit some wild behaviour as well. For instance, leopards in the wild and in zoo eat their prey (food) off the ground. But the 11-month old cub would carry its food to the top of a tree, sit there on top and eat – now that is the wild behaviour. It was a very playful creature, but it couldn’t play much because the enclosure was too small. And so, she would sit in a place and move her neck in a particular angle continuously from one direction to other – that was her stereotypic behaviour.”

This study is part of the Wildlife Biology Post Graduate Degree Research Project of Janice Vaz without any external funding. The professor and his team have communicated the results of the study along with their recommendations with the participating zoos that did kindly cooperate with them. “But we cannot expect immediately much from the zoo authorities”, explains Janice. “Today zoos are losing their status as ‘a place for animals kept on display’. They are being converted to zoological parks that facilitate species conservation. But even then, for most local zoos, changes such as increased enclosure size and habitat enrichment are difficult to implement because of constraints in space and funds.” What can be hoped for is that in the future design of new zoos the policy makers pay attention, and take measures to ensure that our wild animals get their due.