Monitoring stress in wildlife: how to do it and why does it matter? (Summer 2009) By Ben Dantzer

February 6th, 2012 | Research

A common attribute among all animals (including humans) is the stereotypical physiological response to a stressor. Whether it is from your workplace, family, or even the continual abysmal performance from your favourite hockey team (Leafs), we all experience some sort of stress in our daily lives.

In our recent evolutionary history, humans have had to deal with a number of life_threatening stressors such as dangerous encounters with animals or starvation. For example, upon an encounter with a grizzly bear, the body immediately starts to mount a two_pronged stress response. Firstly, adrenaline and other chemicals called catecholamines are released instantaneously to mount the widely known “fight or flight” response. Secondly, stress hormones (glucocorticoids), the second line of defense, are released within 3 minutes of this encounter, and help us cope with the dangerous situation. For example, the release of stress hormones helps to mobilize energy stores (glucose and free fatty acids) and improve blood flow to important areas (muscles) and away from non_essential areas (digestion).

While the temporary presence of stress hormones helps us cope with such immediate stressors, prolonged circulation of these stress hormones can be detrimental to our health. For example, chronic stress can reduce our ability to fight off infections and may lead to hypertension and other cardiovascular problems. For these reasons, medical doctors often warn us to take measures to avoid or reduce chronic stress.

Wild animals also experience a variety of daily stressors, ranging from harsh weather, starvation, or the presence of predators. However, human activities and alteration of wildlife habitat has arguably become the most severe source of chronic stress in wildlife. Highway traffic, habitat alteration/destruction, and even city lights and sounds are likely a primary source of stress in the daily lives of many animals. Human activities can even induce chronic stress in wildlife in relatively remote areas. For example, Dr. Scott Creel and colleagues at Montana State University showed that snowmobile activity in remote National Parks in the United States significantly increased stress hormone levels in both elk and wolves. However, few additional studies have actually addressed how chronic stress affects wildlife.

Chronic stress can have several negative consequences in humans, but it also likely has some detrimental effects on wildlife (e.g., reduction in survival, suppression of reproduction). Therefore in our rapidly changing world, not only do wildlife have to cope with habitat loss, but they also have to do so with elevated stress hormone levels. This situation may lead to reduced population sizes and also reduce the ability for wildlife populations to respond to other natural stressors such as harsh weather or food_shortages. Such a recipe could lead to instability and crashes in wildlife populations.

Although we know that human activities impose chronic stress upon wildlife and that chronic stress in humans is harmful, we still know very little about how chronic stress affects wildlife populations. Because human activities are likely to intensify in the future, it is imperative that we document stress hormone levels in wildlife and also determine how chronic stress can affect survival and reproduction.

As a part of my PhD research, I am collaborating with Dr. Rudy Boonstra, at the Centre for the Neurobiology of Stress, at the University of Toronto, Scarborough, to develop non_invasive methods to measure stress hormones in North American red squirrels. Historically, stress hormone levels were documented by obtaining blood samples. However, stress hormones can also be measured relatively non_invasively in fecal samples from wildlife. This technique requires little expertise because fecal samples can be collected via live_trapping or by simply collecting fecal samples soon after defecation.

To measure stress hormone levels in fecal samples, it is critical to validate the laboratory techniques. This is a crucial step that involves showing that changes in stress hormone levels in the blood are reflected in the feces. In other words, we need to document that we are actually measuring stress hormone levels in the feces rather than some other substance. The key problem is that the liver degrades the stress hormone and excretes complicated breakdown products into the intestines. It is these metabolites that we analyze in feces. Dr. Rupert Palme at the University of Veterinary Medicine in Vienna, Austria is helping us identify the primary metabolites.

With financial assistance from CAHT, I am currently in the process of finishing these laboratory analyses to finish the validation of this technique. The outcome will be a robust laboratory assay that can be used to measure stress hormones in the feces of red squirrels.

Dr. Boonstra and I are developing this non_invasive technique so that we and other biologists can monitor stress hormone levels in red squirrels across North America. Because red squirrels live in both remote areas relatively free of human activities and also in urban areas, they represent an excellent study animal to monitor chronic stress in wildlife and also determine the effects of this chronic stress. Our hope is that other biologists will use similar non_invasive techniques to monitor stress in wildlife so that we have a more complete picture about how human disturbance affects animals. Gathering such basic information is essential for us to predict how wildlife populations are going to respond to increased human activities (Ed. Note: including being caught by live-trapping) in the near future.

Benjamin J. Dantzer is a PhD Candidate

Ecology, Evolutionary Biology, and Behavior Program

Department of Zoology, Michigan State