Stress Levels in Wildlife on the Urban Edge

If you live in or near a city, chances are you may see or have had some type of run-in with wild animals. From squirrels, to deer, to larger carnivores, wild animals are navigating an increasingly urban environment. As city populations continue to grow, interactions between humans and wild animals will only become more common as both work to find their place in a changing world.

Current research is investigating the impact that living in or near these urban environments has on wildlife. It is suspected that these urban areas increase the stress that wildlife feels, but the research into this is ongoing. Understanding the stress felt by wildlife provides insight into their overall health, as exposure to long term stress can decrease their immunity against diseases and shorten their lifespan. This research will be an important part of determining successful conservation methods for the species found near urban environments. 

Recent studies (Carroll et al 2021 and Robertson et al 2023) found that cortisol levels, a hormone released during periods of stress, were higher in coyotes (Canis latrans) and bobcats (Lynx rufus) living near urbanized areas than those in more rural, remote environments. Another study focused on white tailed deer (Odocoileus virginianus) found that living near urban environments did not play a role in deer cortisol levels. Their findings indicate that stress caused by urbanization may differ by species, and continuing to study the levels of cortisol in the different wildlife that frequent urban areas is a promising way to understand their impact. 

Cortisol can be collected from animals in a variety of ways, including from blood, saliva, hair, or fecal samples (scat). Utilizing animal scat is a non-invasive way to study the stress levels of an animal, as well as other factors such as their diet and diseases they may have. Non-invasive research techniques are one way to avoid or reduce any stress that wildlife may feel. As part of Felidae’s Wild Cat Health Project, we are collecting fecal samples from bobcats and pumas (Puma concolor) in the Greater San Francisco Bay Area and Orange County to better measure the impacts of urban expansion on wild felid health. Scat samples are found with the help of a specially trained scent dog, and are analyzed for cortisol levels to better understand the amount of stress these animals may be under. Findings from our 2023 samples revealed high cortisol levels in all samples, showing that felids in the Bay Area are feeling the stress of living near humans.

In a study from 2019, the body conditions of pumas in more developed versus less developed San Francisco Bay Area habitats were studied. Looking at body conditions, or the amount of fat and muscle present on an animal, can provide information about the animal’s health. This study found that while pumas in both location types had good body conditions, those in less developed areas were slightly better than those in urban areas. This is where understanding cortisol levels through scat collection is important because it can provide insight into whether the pumas with lower body conditions differ in their stress levels compared to the others.

While there is still much to be understood regarding stress in urban wildlife, the bottom line is that living near these urban environments does have an impact on wildlife. These landscapes provide more food options such as garbage or roadkill, but also increase the chance of interactions or conflict with humans and exposure to disease. Through research such as the scat sampling that Felidae conducts, we are beginning to gain a better understanding of the ways that human life and urbanization may be impacting our wildlife counterparts. 

References

Carroll, R. P., Litvaitis, M. K., & Foxall, T. (2021). Bobcat Hair Cortisol Correlates with Land Use and Climate. The Journal of Wildlife Management, 85(4), 772-781.

Coon, C. A., Nichols, B. C., McDonald, Z., & Stoner, D. C. (2019). Effects of land-use change and prey abundance on the body condition of an obligate carnivore at the wildland-urban interface. Landscape and urban planning, 192, 103648.

Heimbürge, S., Kanitz, E., & Otten, W. (2019). The use of hair cortisol for the assessment of stress in animals. General and Comparative Endocrinology, 270, 10-17.

Potratz, E. J., Brown, J. S., Gallo, T., Anchor, C., & Santymire, R. M. (2019). Effects of demography and urbanization on stress and body condition in urban white-tailed deer. Urban Ecosystems, 22, 807-816.

Robertson, K. E., Ellington, E. H., Tonra, C. M., & Gehrt, S. D. (2023). Stress in the city? Coyote hair cortisol varies with intrinsic and extrinsic factors within a heavily urbanized landscape. Science of the Total Environment, 901, 165965.