Main Cause of Animal Deaths: A Human Problem

The main cause of animal deaths is a stark reminder that our actions have a direct impact on the lives of other creatures. A staggering 70% of animal deaths are caused by human activities.

Pollution, in particular, is a major contributor to animal deaths, with plastic waste alone killing over 1 million birds and 100,000 marine animals every year. This is a tragedy that can be prevented with simple changes to our daily habits.

Human neglect and abandonment are also leading causes of animal deaths, with many animals suffering from starvation, dehydration, and exposure due to being left behind or discarded by their owners.

Broaden your view: Examples of Human Wildlife Conflict

Insects are among the most numerous and diverse animals, but understanding their causes of death is especially difficult due to their size and diversity.

Some insect species are viewed as pests, and commercial interest in understanding their natural causes of death has led to studies reviewing the causes of death of agriculturally relevant insects.

These studies use a combination of field observations and population modeling to estimate the effect of eliminating a given cause of death on the overall mortality rate.

Interestingly, if predators disproportionately target weak or sick prey, eliminating their predators may have only a small effect on the overall mortality rate because the same individuals who are vulnerable to predation are also vulnerable to dying soon from disease or starvation.

Animal-encounter mentions reported as underlying cause of death in the United States from 1999 to 2016 show that nonvenomous animals were responsible for 3638 mentions, while venomous animals were responsible for 1500 mentions.

Here is a breakdown of the top animal-encounter mentions reported as underlying cause of death:

Wild vertebrates face numerous threats to their survival, and understanding the causes of death in these animals is crucial for conservation efforts.

Predation is a leading cause of death in wild vertebrates, with many species falling prey to predators such as wolves, bears, and mountain lions.

Habitat loss and fragmentation can lead to isolation and reduced access to food, water, and shelter, making it difficult for animals to survive.

Human activities like hunting and poaching are significant contributors to mortality rates in wild vertebrates.

Disease is another major cause of death in wild vertebrates, with many species susceptible to diseases such as rabies, distemper, and parvovirus.

Climate change is altering ecosystems and disrupting the delicate balance of nature, making it harder for animals to adapt and survive.

Vehicle collisions are a common cause of death for many wild vertebrates, especially those that live near roads or highways.

Human-wildlife conflict is a significant issue, with animals often coming into contact with humans and suffering injuries or fatalities as a result.

Insects are among the most numerous and diverse animals, but also the smallest, making them difficult to monitor on an individual level.

Their diversity and size make it challenging to understand their natural causes of death, which is why some insect species are viewed as pests and commercial interest lies in understanding their natural causes of death to devise more effective management strategies.

Eliminating predators may have only a small effect on the overall mortality rate of an insect population, as the same individuals who are vulnerable to predation are also vulnerable to dying soon from disease or starvation.

Insect populations can be difficult to monitor, but studies have used a combination of field observations and population modeling to estimate the impact of eliminating specific causes of death on overall mortality rates.

Some insect species are viewed as pests, and understanding their natural causes of death is crucial for devising effective management strategies.

Research has shown that some causes of death, such as predation, may have a limited impact on overall mortality rates if the same individuals are vulnerable to other causes of death.

Fig. 1 shows the dead body of a Chinese spot-billed duck, which was severely emaciated, with a Keel Score of one out of five. The duck had been bitten multiple times, with three bite wounds found on its body surface.

Take a look at this: Duck Billed Platypus Venom

The bites were located on the duck's chest, belly, and limb, and swabs were collected from each bite point, but the DNA test was not performed on the limb bite due to decomposition. The feathers on the duck's back had been plucked and its neck had been bluntly cut.

The duck's body was collected 10 days after its release, and the upper part from the neck was lost, which made it difficult to identify the animal species responsible for the bites.

Discover more: Massasauga Rattlesnake Bite

Determining mortality risks is crucial to understanding the main cause of animal deaths. Compensatory mortality, where mortality due to a certain cause is replaced by mortality due to another cause when the first is removed, has been noted in many diverse species and ecosystems.

In a study on cormorants along the Columbia River in Oregon, researchers found that cormorants selectively preyed on poorer-condition juvenile steelhead salmon, which would likely have succumbed to harsh conditions and competition in the ocean anyway.

Mortality risks can be complex and influenced by ecological context. For example, if chronic illness made animals less effective at competing for food in a dense population, death by starvation may occur first and compensate for some disease-related mortality.

In some cases, cause-specific mortality really is irreplaceable, as demonstrated by a study on plant chemical defenses against wheat stem sawflies.

Determining the significance of competing mortality risks is crucial for understanding how interventions can impact wild animal populations. This involves considering how actions to protect animals from specific causes of death could influence population sizes, lifespans, and alternative causes of death.

Compensatory mortality, where mortality due to a certain cause is replaced by mortality due to another cause when the first is removed, has been observed in many species and ecosystems. For example, cormorants along the Columbia River in Oregon selectively predate poorer-condition juvenile steelhead salmon, which would likely have succumbed to harsh conditions and competition during their first winter in the ocean.

In some cases, removing a cause of death can actually increase mortality due to another cause. Researchers found that removing coyotes over winter reduced the rate of mule deer deaths by predation, but did not increase their overall survival rates, as they observed increased mortality due to starvation.

The degree to which mortality due to a particular cause is compensatory depends on ecological context. For example, if chronic illness made animals less effective at competing for food in a dense population, death by starvation may occur first and compensate for some disease-related mortality.

Research suggests that mortality risks compete under different conditions, and studying mortality dynamics in a snapshot of a population's present conditions is not enough. We should also model how mortality risks compete under different conditions to fully understand the impact of interventions.

Table 1 provides a fascinating look at animal-encounter mentions reported as underlying cause of death (UCD) and multiple cause of death (MCD) in the United States from 1999 to 2016.

According to the data, nonvenomous animals were responsible for 2138 UCD mentions and 2567 MCD mentions, resulting in a difference of 429 mentions and a percentage difference of 20. This suggests that nonvenomous animals are more likely to be involved in multiple cause of death situations.

The ICD-10 code W55, which represents "bitten or struck by other mammals", had the highest number of UCD mentions at 1314, followed closely by W54, "bitten or struck by dog", with 553 mentions. In contrast, W53, "bitten by rat", had the lowest number of UCD mentions at just 3.

Venomous animals, on the other hand, were responsible for 1500 UCD mentions and 1713 MCD mentions, resulting in a difference of 213 mentions and a percentage difference of 14. This indicates that venomous animals are also more likely to be involved in multiple cause of death situations.

Here are the top 5 animal encounter mentions for UCD and MCD:

The rate ratio of MCD to UCD mentions for nonvenomous animals is 1.20, indicating that nonvenomous animals are more likely to be involved in multiple cause of death situations. For venomous animals, the rate ratio is 1.14, suggesting a similar trend.

Expand your knowledge: Common Snapping Turtle Growth Rate

Wolves are highly selective hunters, targeting specific prey species based on factors like age, size, and health.

Their preference for old or weak prey reduces competition for younger, healthier animals, which helps maintain a balance in the ecosystem.

Wolves often hunt cooperatively, working together to corner and capture their quarry.

This coordinated effort allows them to take down prey much larger than themselves, like elk or moose.

Their hunting strategy is also influenced by the time of day and season, with wolves typically hunting at dawn and dusk when their prey is most active.

In areas with abundant prey, wolves may even hunt at night, taking advantage of the cover of darkness to stalk their quarry.

You might enjoy: Sharp Tailed Grouse Hunting

Predation is the leading natural cause of death for terrestrial mammals, birds, and reptiles. It's especially true for juveniles, which is a crucial stage in their development.

Most studies focus on adults and large-bodied species, which can lead to a biased account of cause of death. This is because accidents involving small animals often go unreported, inflating the number of deaths caused by hunting rather than vehicle collisions.

Research on juveniles and small mammals is desperately needed to get a more accurate picture of cause-specific mortality. This would help us understand the replaceability of different sources of mortality and make interventions more effective.

Fish and juvenile amphibians are still seriously lacking in data on cause-specific mortality, especially relating to juveniles. They spend some or all of their lives underwater, making it challenging to study their deaths.

Biologging technologies, such as pop-up satellite archival tags and acoustic telemetry, could enable more research on cause of death in aquatic environments. These technologies could help us better understand predation and other causes of death in fish and juvenile amphibians.

Insects face surprising challenges that would surprise us, such as developmental abnormalities and drowning during rainy weather. For example, many whiteflies die as a result of poorly understood developmental abnormalities.

A different take: Afghanistan Fish

Cold temperatures can lead to reduced birth weights in stags, making them more likely to die in their first few years of life.

Stags are more sensitive to environmental conditions than hinds, which means they're more likely to die due to harsh weather or competition for food.

High population density on the island of Rum leads to increased competition for food, resulting in higher calf mortality rates.

Calves born in areas with high-quality grazing, such as bentgrass and fescue grasslands, are more likely to die due to intense competition for food.

The condition of a calf at the end of summer is a major factor in determining its survival over the winter months.

Males, or stags, are more likely to die than females, or hinds, because they grow faster and require more food, making them more susceptible to competition.

A unique perspective: American Bald Eagle Food Chain

Humans have a disproportionately huge effect on other species, causing more than 25 percent of the deaths among vertebrates globally. This staggering statistic comes from a recent study that analyzed 42,755 animal deaths in 1,114 published studies.

The study found that 28 percent of animal deaths were directly caused by humans, with larger animals being more likely to be killed by humans than smaller species. Adult animals were also more likely to be killed by humans than juveniles.

Humans' impact on the planet is not limited to direct causes of death, but also includes habitat loss and other land use changes that reduce habitat. This is evident in the fact that 75 percent of Earth's land surface is affected by human activity.

The study's findings highlight the significant role humans play in shaping the fate of other species. It's a wake-up call that should prompt us to consider the consequences of our actions on the planet.

Worth a look: American White Ibis Habitat

Deformities can be a significant cause of animal deaths, with approximately 25% of animal deaths attributed to congenital defects.

Many animals are born with physical deformities that can make it difficult for them to survive. For example, a study found that about 12% of cattle are born with clubfoot, a condition that can cause them to be unable to walk or stand properly.

Accidents, on the other hand, can be caused by a variety of factors, including human error, environmental hazards, and animal behavior. For instance, a study found that about 30% of animal deaths are caused by accidents, such as being hit by a car or falling from a height.

Red deer are susceptible to various accidents, including falls and drowning.

High rainfall in the spring and autumn can lead to a reduction in both adult and calf survival, presumably because it negatively impacts plant growth and food availability for the winter.

Road traffic is also a significant threat, with an estimated 1% of the total UK population killed on roads each year.

Discarded items such as netting, twine, snares, barbed wire, and fishing nets can be deadly for deer, particularly in coastal regions.

Deer can also become entangled in fishing wire and drown or be latched to rocks and starved to death.

For your interest: Blood Tracking Dog Breeds

Deformities and stillbirth can be a devastating reality for young calves.

In some cases, calves are born with congenital defects that can be fatal.

Five out of 31 calves born in a study were stillborn, which is a staggering 16%.

Calf deformities can range from shortened hoof tendons to perforated skulls, all of which are invariably fatal.

Some calves with skeletal defects can live for several months, but malnutrition often proves to be their downfall.

A red deer was born without eyes or eye sockets, a truly bizarre congenital abnormality.

Malnutrition is responsible for almost 90% of calf deaths, making it the leading cause of mortality among yearlings.