September 9, 2022

Thermal imaging technology used to be heavy, bulky, and difficult to use, but today, scientists can fit infrared cameras into spaces as small as a bird nest box. Paul Jerem, a Marie Curie Global Fellow at Tufts University, uses thermal imaging to study body surface temperature and its relationship to stress and energetics — his PhD work focused on associations between body surface temperatures, acute stress, and energy reserves in blue tits (Cyanistes caeruleus).

“People are constantly looking for new opportunities to use this technology,” Jerem says. 

Over the past few decades, researchers have leveraged thermal imaging in numerous wild animal studies, using body surface temperature to investigate thermoregulation in Egyptian fruit bats (Rousettus aegyptiacus), parasitic infections in Spanish ibex (Capra pyrenaica), and behavior in giant honeybees (Apis dorsata).

Now, with a Wild Animal Initiative grant, Jerem and Tufts University Professor Michael Romero plan to point their infrared cameras at juvenile house sparrows (Passer domesticus) to better understand what body surface temperature might tell us about stress and energy reserves in young birds. Altricial birds, who need intensive parental care until they mature, suppress parts of the physiological stress response that are active in adult birds, so it can be more challenging to measure their internal state. Using noninvasive thermal imaging systems planted in nest boxes, Jerem seeks to figure out how researchers might use body surface temperature to monitor young wild birds, and in doing so, learn more about their welfare. 

Stress signals in young birds

Jerem, an early-career researcher, doesn’t have “the usual scientist backstory,” he says. At 23, he landed his dream job as the graphic lead of a video game company, but the commercial nature of the field limited his creativity and pushed him to look for a new profession.

Jerem pursued nature photography for a time, blending his interest in wildlife with his background in art and design. He recalls hour-long drives to the countryside, where he photographed a range of birds, mammals, and numerous insects. His observations left him with a sense of wonder, including a memorable morning when he watched dragonflies emerging from their larval cases and unfurling their shimmering filigree wings.

Jerem realized what he enjoyed most about photography was learning about the animals and environments featured in his pictures. With that, Jerem turned to science, completing an undergraduate degree in biology while working full time and going on to earn his PhD from the University of Glasgow. 

“My scientific work has been relatively varied, but the common thread is that I'm interested in how wild animals cope with changes in their environments,” Jerem says. “I’m motivated to understand what they’re doing and why they’re doing it.”

Jerem studies stress physiology, looking at the mechanisms that wild animals use to respond to their environment. When an animal encounters a predator or becomes frightened by a loud noise, their autonomic nervous system quickly reacts to generate measurable hallmarks of stress such as increased heart rate and rapid breathing. 

The sympathetic nervous system (SNS) controls classic “fight or flight” responses. There’s evidence that in some animals, such as songbirds, a subsystem of the SNS called the hypothalamic pituitary-adrenal (HPA) axis is suppressed in juveniles. Vulnerable altricial birds aren’t mobile and can’t get away from stressors, being entirely dependent on their parents to feed and care for them. Since they can’t respond to stressful events, it’s possible that this particular stress response is suppressed to avoid harm to their development until they gain mobility and independence. However, this makes it harder to monitor stress in young birds, because they’re not generating the same stress signal as adults. 

Jerem wants to know if other stress-related physiological systems are active in altricial birds, and if they are, scientists could use these indicators to study juvenile bird welfare. From previous lab studies, Jerem knows that heartbeat patterns can reveal what part of the autonomic nervous system is activated and provide a window into metabolic rate. By looking at body surface temperature and heart-rate variability, Jerem wants to build a better understanding of the relationship between these metrics.

Thermal imaging for welfare

Thermal imaging can help researchers study a bird’s rate of breathing, as seen in this video. Video courtesy Paul Jerem.

Through his fellowship, Jerem already has funding to study adult birds in the lab and field. He will use advanced lab equipment to determine how heart-rate variability relates to specific body surface temperature patterns in adults. But he will use Wild Animal Initiative’s grant to look at juvenile birds, investigating how stress physiology changes as a bird matures. His team will use lab results to guide further study of wild birds, seeing if body surface temperature dynamics differ between adults and juveniles.

“What we’re trying to do with thermal imaging is take a different approach from more invasive methods,” Jerem says. “It’s possible we can infer what’s going on inside the bird’s body by looking at temperatures on the outside of the body.” 

Jerem will subject the young birds to various stressors, such as simulating predators’ attacks with calls or smells that could activate stress responses in nestlings. Then, he will compare body surface temperature readings from these birds to others taken from adults in the lab and field in similar situations.

This noninvasive technique represents a promising way to measure welfare in young, free-living birds. In lab studies, researchers use sensors or take blood samples to study the hormonal processes behind stress, but these methods aren’t practical in the wild and only cause further stress. Innovative and less invasive ways to measure welfare, like Jerem’s methods, will play a foundational role in the growing field of wild animal welfare.

If validated, the low-cost thermal imaging cameras equipped with tiny Raspberry Pi computers could be adapted to study other animal species, because the underlying physiology mechanisms dealing with stress are essentially identical across birds and mammals. Jerem wants to ensure that the technology is open source and broadly available for other researchers to use. 

“Although we are also interested in the fundamentals of how wild animals are dealing with changes in their environments, there’s huge potential for applying this technology to studying welfare,” Jerem says. 

The welfare angle

Young wild animals can have dramatically different life experiences than adult wild animals, and it’s important to understand those differences to better assess their well-being. Since many wild animals die before reaching adulthood, learning how to improve their lives could have an enormous impact on wild animal welfare. 

If body surface temperature fluctuations are linked to stress in juvenile birds, this metric could become another handy indicator in a welfare biologist’s toolkit.

“What’s great about physiological state is that it’s a very good quantitative measure of welfare,” Jerem says. “It’s one way to gather hard data on how individuals cope with stress, whether it’s caused by human disturbance, climate change, or something else.”

Jerem says welfare blends well into his physiology studies, and much like photography made him look at the natural world in a different way, “looking at wild animals from the angle of welfare brings a new perspective.” 

“To me, studying welfare is a no-brainer, especially in conservation terms,” he adds. “It’s something that we should consider, and the fact that we haven’t considered it much to date is a massive omission.” 

This is the fifth story in a series of features on our spring 2022 cohort of grantees. Please subscribe to our newsletter to get future stories delivered straight to your inbox.