The image of stress: Detecting stress in animals using thermal imaging

It’s not just humans that get stressed: animals do too. Predators, human disturbance, and food availability can all cause physiological changes in animals. How do you measure the effect of stress on an animal? Researchers at the Institute of Biodiversity, Animal Health and Comparative Medicine at the University of Glasgow are looking at using the animal’s temperature to monitor its physiological state.

By Elizabeth Thomsen

It’s not just humans that get stressed: animals do too. Predators, human disturbance, and food availability can all cause physiological changes in animals.

How do you measure the effect of stress on an animal? You could take a blood sample to measure hormone levels, or fit a device to measure their heart rate. However, both of these tactics involve capturing an animal, are limited to animals that are easily caught, and can actually cause the stressful response.

Taking the temperature of stress

Instead, researchers at the Institute of Biodiversity, Animal Health and Comparative Medicine at the University of Glasgow are looking at using the animal’s temperature to monitor its physiological state. Just like we blush when embarrassed, or get cold fingers and toes when frightened, different parts of animals’ bodies change temperature when they are under stress.

Animals’ temperatures can be measured using thermal imaging cameras, which pick up body heat. Dr Paul Jerem says: “We want to develop something that can be used in the field, and we want to measure [the animals’ temperature] without influencing them.”

The team is using this technique in birds such as wild Blue Tits (Cyanistes caeruleus). The researchers use the thermal camera in much the same way a digital camera would be used. Techniques from wildlife photography and filmmaking are used to create setups where they can video the birds without disturbing them.

A snapshot of stress

The researchers have looked at acute stress in birds, and at longer term processes that may relate to chronic stress. For the acute stress measurements they used a box with a tray of birdseed to bring the bird in front of the camera. The bird was recorded while it was undisturbed, and then the researchers closed the box, capturing the bird and creating a mild stressor. The bird’s response was recorded by looking at the temperature around the eye of the bird (where there were no feathers). The researchers could see patterns of temperature change that related to stress hormone levels.

Researchers also examined the relationship between body condition (how heavy an animal is for its size) and temperature. The body condition of an animal is a good reflection of its energy reserves. And, if energy reserves are diminished (for example, due to lack of food), then they can be protected by lowering the metabolic rate. A lower metabolic rate is associated with reduced body temperature. The researchers hypothesized that birds in poor condition would have a lower temperature, and this was confirmed by their experiments. In both the breeding season and in winter, birds with lower body condition had a lower temperature. These lower temperatures were also associated with higher hormone levels associated with stress, as measured by blood tests.

The scientists would like to confirm their results by performing controlled experiments where the body condition of birds is manipulated, and their temperature is measured. The body condition of the birds could be changed by techniques like changing the number of chicks in the nest, making the bird work more or less hard.

“We want to develop something that can be used in the field, and we want to measure [the animals’ temperature] without influencing them.”

A bird’s eye view

While the researchers have been focussing on birds, the thermal imaging technique could potentially be used to monitor any terrestrial warm-blooded animal that can be filmed. Only a very small area of bare skin is needed for the temperature measurements. In the blue tits, this area is a small ring of skin around the eye. Despite the size, Dr Paul Jerem says they can “see a lot through this tiny window.”

The team would like to apply their technique to work on both wild and captive animals. Thermal imaging also offers a way to monitor the welfare of captive animals, such as chickens. And better welfare isn’t just a sensible ethical decision, it means more eggs are produced.

The scientists hope to detect when a wild animal population is in trouble. Falling population numbers are often the first sign that animals are struggling, however by that stage it may be too late for conservationists to help. Dr Jerem says, “we hope we can use a snapshot from a few individuals to give us an idea of the state of the population.”

What’s next?

There is still some work to be done before this imaging process can be used by conservationists and animal welfare experts. Along with working on understanding the relationship between physiology and temperature, the scientists are attempting to make the technique as economical and easy to use as possible. They would like to further automate the analysis process, and would welcome collaborations from mathematicians specialising in machine learning. They are also working on using open source software for all stages of the work, and using small cameras and computers such as the Raspberry Pi.

This novel technique has enormous potential for investigating and monitoring the responses of animals to environmental challenges. Making the technique accessible, cheap, and easy to use, will have great impact in conservation, ecology, and animal welfare.

Photo credit: Paul Jerem