The world is facing a biodiversity crisis, mainly due to the death of wild animals. A major cause of harm to wild animals is human activity, otherwise known as ‘anthropogenic factors.’ These anthropogenic factors can be direct, such as hitting a deer with a car, or indirect, such as outdoor cats killing birds.

This study investigated the causes of injury, illness, and death for wild animals in Canada from 2009 to 2019 using data collected from the Canadian Wildlife Health Cooperative (CWHC) and 19 wildlife rehabilitation centers (WRCs). Over 160,000 records were evaluated: 18,540 from the CWHC and 144,846 from WRCs.

The CWHC conducts post-mortem examinations on dead animals submitted to them, whereas WRCs receive live animals and gather information on their circumstances and conditions. Combining this data develops a better understanding of how wild animals are impacted by human activity, as each option alone doesn’t paint a full picture of the anthropogenic factors that affect their health and welfare.

Trauma, mainly caused by anthropogenic factors, was the leading cause of death for both the CWHC and WRCs and the number one reason for admission to WRCs. This includes vehicle collisions, window strikes, cat and dog attacks, and projectile strikes. For WRCs, vehicle collisions were more common in adult animals than juveniles, while cat attacks were more frequently seen in juvenile animals than adults. It’s worth noting that most fatal cat attacks in the U.S. are thought to involve unowned cats. For larger animals brought to the CWHC, such as big cats, wolves, and bears, projectiles (like gunshots) were the top cause of trauma.

Situational reasons, such as parental loss or being in an unsuitable location, were responsible for over one-third (37%) of all animals admitted to WRCs. Parental loss affected nearly half (48%) of all mammals and was among the top three most common causes of admission for all bird species. Nest or habitat disturbance was a high-ranking reason for reptiles, amphibians, and mammals brought to WRCs. Amphibians, reptiles, and ungulates like deer were more likely to be brought in due to illegal or improper possession than other types of animals.

Close to one-third (29%) of animals who had been killed or euthanized and brought to the CWHC were due to conflict with humans, with many more mammals killed for this reason than birds. While felids such as mountain lions, lynxes, and bobcats contributed to less than 2% of all conflicts, they were the most common type of animal to be killed due to conflict. Yet, over 40% of them were diagnosed as clinically and behaviorally normal.

The authors point out that carnivores, such as bears, big cats, and foxes, are more likely to be perceived as threatening and so are more likely to be killed due to conflict. This is despite the fact that in reality, smaller species with low conservation interest, such as rats, are associated with more damage in rural and urban areas. As such, they highlight that education on the actual risks of these larger carnivores could improve people’s perception of them, potentially reducing the number of animals killed due to human conflict.

It was also found that non-human factors, such as infection, inflammation, and starvation, were significant causes of mortality in the CWHC data and were far more common in animals submitted to the CWHC than those brought to WRCs.

While combining data from the CWHC and WRCs helps provide a better understanding of the impact humans have on wild animals, this information relies on the public bringing animals to these centers in the first place. As such, there’s likely a skew towards animals living close to humans, along with those who are of more interest to humans. Moreover, as many animals are injured or die in the wild and are not brought to a wildlife center, the total number of deaths and injuries due to anthropogenic factors is likely to be much higher than reported in this study.

Understanding the causes of injury, illness, and death for wild animals can help animal advocates design more effective interventions to save them. For example, as outdoor cats are a leading cause of trauma and death for small wild animals, young ones in particular, sterilization programs may be effective in tackling this issue. Additionally, educational programs aimed at improving people’s perception of large carnivores may help to reduce the number that are killed as a result of human conflict.