Using Behavioral Imaging To Study Animal Welfare

Monkeys and non-human apes — often called “non-human primates” or NHP — are often kept in captivity at zoos and as test subjects in biomedical research. While many animal advocates want to end the practice of keeping NHP in captivity, those who are currently living in these conditions deserve to experience the highest standard of animal welfare.

As intelligent and social animals, NHP use a combination of body posture and positioning of limbs to convey emotions and communicate with each other. In this study, the authors review technological advances in behavioral imaging techniques to study NHP body language as a means to enhance their welfare.

Behavioral tracking or imaging systems use digital cameras and analytical software to track NHP body position at any given point in time (called pose tracking) and reveal the behavior they’re performing at that moment (called behavioral identification). For example, while pose tracking may identify that a monkey is seated, behavioral identification clarifies if the monkey is seated for foraging or for grooming her neighbor. 

The review focuses on behavioral tracking systems in the context of (1) reducing pain and distress in NHP, (2) promoting “natural” behaviors in captive NHP or wild NHP populations, and (3) improving the welfare of NHP used in laboratory research. While the authors of this study were in support of zoos and animal research, the information can also be used in advocacy settings. 

Studying pain and stress in primates is challenging. They tend to mask their pain behaviors when being observed by humans, which makes observational studies difficult. By the time an NHP reveals impaired behavior due to stress or illness, it’s often too late to intervene for the animal’s health. Furthermore, physiological measures (such as blood tests) can be stressful. Behavioral imaging is able to detect early signs of pain — such as impaired movement, favoring limbs, over-grooming, and hunching — even when these behaviors are subtle. It can also detect stereotypies, a common indication of stress. 

When it comes to tracking pain and stress responses, behavioral imaging has some obvious benefits over human observers. These include reducing the cost of hiring a full-time observer, limiting human bias, and the ability to collect large amounts of data to track behavioral changes over time. However, because different NHP species (and individuals) may respond to pain and stress in different ways, it’s important to have a human observer on hand to interpret the findings. 

The authors also believe that NHP welfare can be improved by assessing their responses to environmental changes and enrichments provided within captive spaces over time. In the fields of conservation and rehabilitation, behavioral tracking can be used to determine the success of newly housed or released animals. The authors foresee using the information from such studies to design better enclosures and habitats where the impacts of ecotourism and stimulants such as lights, noise, and human interactions can be minimized.

Improving the welfare of NHP such as rhesus macaques and marmosets — who are often used in neuroscience laboratory experiments — was explored in the context of the “3Rs” of animal research and big data. Big data refers to the unprecedented ability to collect large volumes of data from neuroscience animal experiments. With this technology, data from past animal experiments can be used to design future neuroscience experiments, replacing animal studies with non-animal methods.  However, the neuroscience data needs to be considered along with behavioral data, which is where behavioral tracking systems come into play. By providing rich, valid behavioral data, these systems can also help reduce the number of primates used in experiments and eliminate the need for some invasive research methods, thus refining the test model. 

The authors frame the use of NHP as test subjects in laboratories as “unavoidable.” This is arguably an opinion, given the alternatives to NHP animal models that are being actively pursued for scientific, ethical, and economic reasons. While the review focuses on NHP behaviors, it is unknown whether these animals express internal states and emotions solely via posture and interactions. In the future, analytical methods that track eye movement and facial expressions are worth considering. 

In the meantime, animal advocates can use this knowledge to push for more behavioral tracking systems in situations where NHPs may be experiencing stress, such as zoos, laboratories, and rehabilitation centers. Until we are able to end the use of NHP in captive settings, it is imperative to find ways of making sure their welfare is as optimal as possible.