The temperature is five degrees below zero. Animal science PhD student Judy Stryker says she’s freezing, but the Siberian tiger she’s observing in a zoo is panting. For him the weather is almost too warm, and he’s panting just a little because that’s the way tigers stay comfortable.

The lions in another enclosure – Stryker says they’re brothers – sit together on a heated pad set in the ground. Unlike their tiger cousins, they find this weather a little cool and enjoy relaxing in the heated area.

Stryker says zoo designers are giving more thought to the comfort and well-being of the animals living there than in past years, when their goal was to make the animal habitats interesting for the people who come to visit. Her research encourages that shift by giving zoos one more factor to consider: thermo-regulation, or how the animals maintain a comfortable body temperature.

“I’m looking at the big cats and trying to compare the different species,” she explains. She studies jaguars, lions, pumas, snow leopards and Siberian tigers and uses a thermal camera to produce images that translate temperature into colour. The results are what Stryker calls “some pretty neat technicolour pictures of animals.”


Her research has a number of goals. One is to develop an understanding of how these animals behave throughout the day in a zoo environment. Her results so far will seem familiar to owners of domestic cats: they sleep a lot. Stryker also says the big cats may be crepuscular, meaning they are most active at dawn and dusk and less active during the day and night, although more work is needed to confirm this.

She’s also hoping to validate the use of the thermal camera to determine the actual body temperatures of the animals. Earlier this year, Stryker and others in a research group led by Prof. Esther Finegan visited a zoo with nine Bengal tigers, where the staff are trying to train their tigers to tolerate rectal thermometers. If the training is successful, one of the zoo keepers will take rectal temperatures while Stryker is taking thermal images. This will allow her to more accurately calibrate the connection between the animals’ core temperatures and the external temperatures captured by the thermal camera: eyes, inner ears, urine and fecal matter as it is voided.

If the thermal camera can provide an accurate way to determine an animal’s internal body temperature, it could provide a non-invasive method of assessing the animal’s health, says Stryker. “We often don’t know that a dangerous carnivore is sick until we see obvious behaviours. This technique could detect a fever or elevated temperature and help us recognize illness sooner.”

Thermoregulation can be a challenge for these big cats. They don’t sweat the way we do, so they pant to get rid of excess heat. Many will lie spread-eagled on their backs, to expose the stomach – where they have the least fur – to the air. They may also seek out shady areas as the day heats up.

“A tiger might be sleeping under a tree for five hours, but he’ll move a little bit every 15 minutes as the shade patch moves, so that he remains in the shade patch,” says Stryker.

When they have access to water, tigers will swim or sit in the water on hot days. So will jaguars, but not as much. At the Toronto Zoo, most of the large cats can be sprayed with misters in the summer to help them cool off.

Some cats, including the Siberian tiger and the snow leopard, grow thick winter fur and are well-adapted to the cold. Others, like the lions and jaguars who live naturally in warmer climates, are comfortable in the warm Toronto summers but curl up together in cool weather and spend time in the cave shelters in their exhibit area. In really cold weather, the Toronto Zoo moves them into heated indoor enclosures.

“Keeping warm uses up a lot of energy for an animal,” points out Stryker, and not being able to reach a comfortable temperature can be stressful for them. But it is overheating that is actually more dangerous since it can cause brain damage or even death.

The next step in Stryker’s work will be to apply this research to exhibit design. “There is so much that goes into the design of zoo enclosures, and now I hope we can add something else: thermal comfort.”

Some of the design elements are simple, she says: making sure the animals have access to sufficient shade, adding in-ground heating pads for the animals that are most sensitive to the cold, and being aware of how the exhibit is oriented to the movement of the sun and the prevailing winds.

While her work is still preliminary, Stryker is excited about the possibilities for better understanding the needs of these animals. “I have always been interested in animal behaviour and animal welfare,” she says. “While it is not easy to find funding to study zoo animals, it’s important work.”