Psychologists know that childhood trauma, or the experience of harmful or adverse events, can have lasting repercussions on people’s health and well-being into adulthood. But while the consequences of early adversity were well researched in humanshumans are not the only ones who can experience adversity.

If you have a rescue dog, you’ve probably witnessed how abuse or neglect they may have experienced earlier in life is now influencing their behavior – these pets tend to be more nervous or reactive. Wild animals also face adversity. Although their negative experiences are easily dismissed as part of life in the wild, they still have lifelong repercussions – just like traumatic events in humans and pets.

As behavioral ecologists, we are interested how adverse experiences early in life can affect the behavior of animals, including the types of decisions they make and how they interact with the world around them. In other words, we want to see how these experiences affect how they behave and survive in the wild.

Many studies in humans and other animals have shown the importance early life experiences in shaping how individuals develop. But researchers know less about how multiple, different instances of adversity or stressors can accumulate in the body and what their overall impact is on an animal’s well-being.

Wildlife populations face many types of stressors. They compete for food, risk being eaten by a predator, suffer from disease and have to deal with extreme weather conditions. And as if life in the wild wasn’t hard enough, humans are now adding additional stressors such as chemical, turn on and noise pollutionas well as habitat destruction.

Given the spread loss of biodiversityunderstanding how animals react and are affected by these stressors can help conservation groups better protect them. But taking into account such a diversity of stressors is no easy task. To address this need and demonstrate the cumulative impact of multiple stressors, our research team decided to develop a wildlife index based on psychological research on human childhood trauma.

A cumulative adversity index

Developmental psychologists began to develop what psychologists now call adverse childhood experiences scorewhich describes the amount of adversity a person experienced as a child. Briefly, this index sums all adverse events—including forms of neglect, abuse, or other domestic dysfunction—that an individual experienced during childhood into a single cumulative score.

This score can then be used to predict subsequent health risks such as chronic health conditions, mental illness or even economic status. This approach has revolutionized many human health intervention programs by identifying at-risk children and adults, which allows for more targeted interventions and preventive efforts.

So what about wildlife? Can we use a similar type of score or index to predict adverse survival outcomes and identify individuals and populations at risk?

These are the questions we were interested in answering our latest research paper. We developed a framework for how to create a cumulative adversity index—similar to the Childhood Adverse Experiences Score, but for wildlife populations. We then used this index to obtain information on survival and longevity of yellow-bellied marmots. In other words, we wanted to see if we could use this index to estimate how long a marmot would live.

A groundhog case study

Yellow-bellied marmots they are a large ground squirrel closely related to marmots. Our research group studied these groundhogs in Colorado at Rocky Mountain Biology Laboratory since 1962.

Yellow-bellied marmots are an excellent study system because they are diurnalor active during the day and have an address. They live in burrows scattered within a small, defined geographic area called a colony. The size of the colony and the number of individuals living inside varies greatly from year to year, but they are normally composed of matrilinesmeaning that related females tend to stay in the natal colony, while male relatives move away to found a new colony.

Yellow-bellied marmots hibernate most of the year, but become active between April and September. During this active period, we observe each colony daily and regularly capture every individual in the population – that’s over 200 unique individuals in 2023 alone. We then mark their backs with a distinctive symbol and give them uniquely numbered rattles so they can be identified subsequent. .

Although they can live up to 15 years, we have detailed information about the life experiences of individual marmots, spanning nearly 30 generations. They were the perfect test population for our Cumulative Adversity Index.

Among the sources of adversity, we included ecological measures such as a late spring, a summer drought, and high predator presence. We also included parenting measures such as having an underweight or stressed mother, late birth or weaning, and maternal loss. The model also included demographic measures, such as being born in a large litter or having many male siblings.

Importantly, we only looked at females, as they are the ones who tend to stay at home. Therefore, some of the adversities listed are only applicable to women. For example, females born in litters with many males become masculinizedprobably from high testosterone levels in the mother’s womb. Females behave more like males, but this also reduces their lifespan and reproductive productivity. Therefore, having many male siblings is harmful for women, but perhaps not for men.

So does our index, or the number of adverse events a marmot experienced at baseline, explain the differences in marmot survival? I found that, yes, it does.

Experiencing even a single adverse event before age 2 nearly halved an adult groundhog’s chance of survival, regardless of the type of adversity it experienced. This is the first record of long-term negative consequences of the loss of a mother in this species.

So what?

Our study is not the only one of its kind. Several other studies have used an index similar to the Human Adverse Childhood Experiences Score wild primates and hyenaswith largely similar results. We are interested in expanding this framework so that other researchers can adopt it for the species they study.

A better understanding of how animals can or cannot cope with multiple sources of adversity can inform wildlife conservation and management practices. For example, an index like ours could help identify at-risk populations that require more immediate conservation action.

Rather than addressing the single stressor that appears to have the greatest effect on a species, this approach could help managers consider how best to reduce the total number of stressors a species experiences.

For example, changing weather patterns driven by global warming trends perhaps creates new stressors which a wildlife manager cannot address. But it may be possible to reduce the number of times these animals have to interact with humans at key times of the year by closing trails or providing extra food to replace the food they lose due to bad weather.

Although this index is still in development, it could one day help researchers ask new questions about how animals adapt to stress in the wild.

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