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EASTMAN, D. Glenn 1934-2024 On Friday, April 12, 2024,...

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Science & NatureGreen TalkMammals and their role in the web of life: Part 2

Mammals and their role in the web of life: Part 2

Part 2:  The current state of wild mammals and how to remediate it

By Theresa Peluso

Because there’s so much to say about the topic of mammals, I have split this article into two parts. Part 1 briefly described the origins of mammals (which began about 200 million years ago), and provided some basic information on their characteristics, number of species (approximately 5,450), population size (about 130 billion), and distribution, as well as their importance in the web of life as sources of food for other animals, population controllers, seed dispersers, and maintainers of soil health and a diverse ecosystem.

A White-Tailed Deer near Almonte (Brent Eades photo)

I also alluded to the current human-caused tragedy that is unfolding; namely, the rapid, accelerating extinctions in all animal species, on a scale that has occurred only five times in the last 500 million years. In less than a century, it is expected that even the much diminished number of species that exist at present will be halved – leaving our planet with fewer than 3,000 species of mammals.

According to, between 1500 and 1900 BCE (Before Common Era), 47 mammal species became extinct.  During the whole twentieth century and the first 16 years of this century, 35 species of mammal have been killed off.  This does not include the decrease in populations of many species, or the species that are now on the endangered list.  Statistics in the World Wildlife Fund’s 2016 Living Planet Index indicate that global wildlife populations declined 58 percent since 1970, mainly due to habitat destruction, over-hunting and pollution.  It is projected that at this rate, 67 percent of wildlife could disappear by the end of next year.  Just some of the species predicted to become extinct in the near future are the rhinoceros, primates, pangolins (a kind of scaly anteater), and giraffes.

The countries with the most mammal species also have the greatest number of threatened species; for example, Indonesia (191 out of 670 species threatened), Brazil (80 of 648 species threatened (the current accelerated destruction of the Amazon rainforest will drastically increase this number), China (73 of 551 mammal species threatened), and Mexico (96 of 523 species threatened).  In Canada, 18 of our 202 mammal species are threatened.

Habitat loss is a major threat, and is the result of expansion of agricultural lands, urban sprawl, logging, and mining.  Like many other animals, mammals need places to hide, eat, drink, and breed, and often have to travel some distance to find what they need.  It is impossible for large mammals to live in micro-habitats, which is what ends up happening as a result of more highways and housing subdivisions criss-crossing the landscape, wetlands being drained, and forests being burned or cut.  Factor in climate change and extreme-weather events like floods, droughts and forest fires, and the options of these mammals are even more restricted. Recreational machines also damage and fragment habitat, and act as a means for invasive species to penetrate forests and other wild areas.  Animals affected include white-tailed deer, mule deer, caribou, elk and moose.

Toxicity, as a result of pesticide use, is another threat.  Because mammals are often at the higher end of the food chain, these chemicals can accumulate to hazardous levels by the time the mammal ingests its prey.

Another threat for freshwater and marine mammals is dead zones, low-oxygen areas in the world’s oceans and lakes. This problem, mainly the result of human activities (sewage and industrial spills and agricultural run-off), are caused by too many nutrients flowing into waterways.  The resulting algal blooms promote the development of a dangerous bacteria called cyanobacteria.  Not only do these algal blooms sicken and kill humans, they also sicken and kill birds and marine mammals.  These algae eventually die, but leave dead zones in their wake, and these are found world-wide.  A 2008 study counted 405 dead zones; One of these dead zones, in the Gulf of New Mexico, measured more than 22,730 sq km in 2017.

Water and air pollution of our oceans is also caused by most ships, including cruise ships, because the especially dirty fuel they use generates extremely high levels of CO2, as well as nitrogen and sulphur oxides.  Given the size of these ships (the largest cruise ships average 220,000 registered tons) and the thousands of kilometres distance they travel, the amount of pollution is huge.  The anti-fouling paint on the hulls of large ships releases heavy metals when the ships are in port.  In addition, ship engines produce vibrations and noise levels that can range from the equivalent of a loud rock concert to the equivalent of a vacuum cleaner.

Cruise ships, in particular, produce large quantities of sewage, bilge, drain and ballast water, and solid waste.  Their passengers produce up to 40 litres of sewage and 340 litres of wastewater per person, per day.  Although many countries have rules regarding the discharge of this waste, these rules are difficult to enforce once the ship is beyond the jurisdictional waters of these countries. With the increase in shipping traffic, including cruise ships, through the now mostly ice-free Northwest Passage, marine mammals such as narwhals, beluga and bowhead whales and walruses are dying.  According to the 2 July 2018 edition of the Science Daily (, this was the effect of vessel traffic:

The most vulnerable marine mammals were found to be narwhals, or tusked whales. These animals migrate through parts of the Northwest Passage to and from their summertime habitats.

“Narwhals have all the traits that make them vulnerable to vessel disturbances — they stick to really specific areas, they’re pretty inflexible in where they spend the summer, they live in only about a quarter of the Arctic, and they’re smack dab in the middle of shipping routes,” said co-author Kristin Laidre, a polar scientist at UW Applied Physics Laboratory’s Polar Science Center. “They also rely on sound, and are notoriously skittish and sensitive to any kind of disturbance.”

Other mammals found to be vulnerable were beluga and bowhead whales. Walruses also were vulnerable because some populations are relatively small and known to live along shipping routes, compared to generally large and widely distributed populations of ringed and bearded seals, which were shown to be less vulnerable.

Plastic pollution is yet another threat.  Many marine mammals, such as whales, dolphins and seals, get entangled in abandoned fishing nets, end up swallowing plastic pieces.  As apex predators, they also suffer from the accumulation of plastic up through the food chain.  Globally, 100,000 marine mammals die each year as a result of plastic pollution, including whales, dolphins, porpoises, seals and sea lions.

Land mammals are also affected. For example, this year in Japan, the 14 Sika deer at a park in Japan died from ingesting huge masses of plastic bags and food wrappers. Out of 51 polar bears in the southern Beaufort Sea area caught and killed in the last 10 years, one quarter had plastic in their stomachs – this was determined to be caused by the bears, famished from the lack of sea ice, rummaging in dumps to find food.

And then there are all the diseases.  Certain diseases target a certain group or species, such as the white-nose syndrome in bats; the Ebola virus in the great apes; the Devil facial tumour disease, a cancer that affects only Tasmanian devils; chlamydia in koalas; plague, which in North America affects mainly prairie dogs, the main source of food for the black-footed ferret; chronic wasting disease, a fatal nervous system disease, which infects white-tailed deer, mule deer, moose, red deer, elk and reindeer.  Other diseases are less selective. Numerous bacterial and viral diseases affect marine mammals, including salmonella, pneumonia, septicemia, influenza, herpes and rabies. Sarcoptic mange, a disease spread by a parasitic mite, affects hundreds of species of mammals. Canine distemper, a virus spread by domestic dogs, is wiping out wild carnivores around the world.  The anthrax bacterium mainly affects herbivores, but also some carnivores, great apes and humans. Although there are some remedies to some of these diseases, it is almost impossible to reach all the mammals affected, or at risk of being affected.

Global heating (the result of increased greenhouse gases from human activity) is yet another problem affecting mammals. Many species require specific temperature ranges to survive, forcing them to migrate to new areas.  Moose are moving farther north to avoid the winter ticks that flourish in warmer temperatures, which are potentially fatal to moose.  Snowshoe hares are finding that their successful strategy of turning white in winter now makes them easy targets for predators when the landscape stays brown and green. Wolverines require persistent spring snow for their dens, and so they’re being driven further north as a result of global heating. American pikas and Alaskan caribou are also migrating to colder regions, even though they may not have access to suitable food sources.  The rise in sea levels as a result of global heating also affects the coastal environments where numerous species dwell, such as various species of sea otters, seals, manatees and polar bears.  The increased temperature of the oceans, the declining ocean turbulence, and the acidification resulting from increasing absorption of carbon in the water, are drastically impacting plankton and other tiny organisms, which form the base of the marine food web.

Overhunting and poaching are yet another cause.  Mammals are hunted for their pelts, their tusks and horns, meat, oil.  In 2011, the Center for International Forestry Research estimated that 6 million tonnes of animals were illegally taken each year.  More than 100,000 African elephants were killed between 2014 and 2017 for ivory.  More than 1,000 rhinos are slaughtered each year for their horns.

Some fishing practices, such as trawling, result in many fish and mammals being injured or killed as by-catch.  Bottom-trawling also damages the seafloor and coral reefs, a critical habitat for many species that form part of the food web.

Noise disturbance is a huge problem, especially for marine mammals.  Considering that human hearing tissue is permanently damaged at 180 decibels, why would humans expose marine creatures to underwater military sonar, which generates sound waves that reach 235 decibels?  These sound waves, which are known to travel underwater for hundreds of kilometres and maintain an intensity of 140 decibels as far as 500 km from their source, can end up causing whales and dolphins to lose their hearing, develop hemorrhages, and die.  Extremely harmful sound waves are also caused by underwater oil and gas exploration, which requires the firing of many dozens of seismic air guns on huge ships to map the ocean floor.  These guns blast pressurized air repeatedly (approximately every 10 seconds, 24 hours a day, over a period of several months) into the depths of the ocean.  Marine mammals are similarly harmed by noise from ship sonar and general tanker traffic.  This constant underwater noise pollution, in addition, disrupts feeding and migration behaviours, masks other normal background sounds, drowns out the communication sounds important for the survival of these mammals, and generally increases their stress levels.

Land mammals are also affected by the noise of machinery, including motor vehicles.  They can suffer auditory damage, which impairs their ability to survive predation.  In addition, the noise from motors can mask the sounds of predators.  As with humans, high levels of background noise can cause an increase in animals’ heart rates and affect their ability to reproduce, feed and forage.

Cars don’t just kill amphibians, birds and reptiles – they kill mammals (other than people) too.  Each year in the state of Maine, roughly 3,000 to 4,000 deer are hit by vehicles.  Other casualties are skunks, porcupines, racoons, squirrels, foxes, wolves, coyotes, moose, elk, bison, antelopes, and bears.  In other countries, vehicles are responsible for 50 percent of the deaths of Florida panthers, and are the largest cause of badger deaths in England.  In Australia, koalas, eastern quoll, brushtail possums and Tasmanian pademelons are victims of vehicle impacts.

Watercraft can also be deadly. In just the first six months of this year, a total of 81 manatees (an endangered marine mammal) have been killed by watercraft in Florida’s waters, according to the Florida Fish and Wildlife Conservation Commission.  This is 11 more than were killed last year during the same time frame. Sight-seeing boaters can also harm whales and dolphins by getting too close to them.  In busy shipping corridors, like the east coast of the United States and Canada, and in the Mediterranean Sea, there is the problem of whale strikes by huge ocean-going vessels.

Pets also kill wildlife.  According to an article in the January 2013 edition of Live Science (, cats kill between 6.9 billion and 20.7 billion small mammals, such as meadow voles and chipmunks, each year.  Although cats are effective at killing vermin like Norway rats and house mice, their hunting skills must be restricted to their owners’ houses and barns to avoid this huge impact on our natural environment.

The situation looks very discouraging.  What actions can we take to turn things around, to provide mammals with a healthy habitat and prevent further species loss?

Part of the solution is political.  We need to work together to vote for political parties and candidates at all levels (federal, provincial and municipal) who will make the natural environment a key element of all their decision-making, and who will work with other countries to promote environmental and species protection – an example is the Rio Accord, which includes 189 signatory countries that have committed to identifying endangered species and habitats. Advertising one’s province as “open for business” is destructive, as we are seeing in our province, and in other countries like Brazil, the United States, and Australia.

As individuals, we also need to actively support organizations that work to identify mammals and actively advocate for species protection, such as the IUCN (International Union for Conservation of Nature), with a membership of over 1,200 governmental and non-governmental organizations. Other more local organizations are Ontario Nature, Environmental Defence Canada, Canadian Wildlife Federation, Canadian Parks and Wilderness Society, and the Ontario Land Trust Alliance.  Working with and learning from Indigenous Peoples; for example, through Plenty Canada, is another important approach. In keeping with Pope Francis’s call for urgent action to stop climate change and to care for the environment, many church groups are adding environmental projects to their traditional works of mercy. In addition, we need to drastically reduce carbon emissions, cut back on what we buy, and ensure that the food and products we buy are grown and produced sustainably.

It goes without saying that as motorists, we need to drive carefully to avoid hitting wildlife.  Replacing motorized recreational activities with non-motorized outdoor activities will enable us to improve our fitness levels, while also hugely reducing negative impacts on wildlife.  Boaters can learn how to minimize their impact on marine life by accessing the following link, courtesy of the Department of Fisheries and Oceans:

Within our own community, we need to encourage our elected officials and responsible agencies to maintain and, where possible, improve landscape connectivity, as well as landscape diversity.  A connected landscape allows mammals to seek suitable habitats and prevents the negative consequences of species extinction and compromised fitness. Diverse and remediated landscapes increase the overall resilience of mammals and provide opportunities for them to adapt. Lastly, because climate change will lead to many unexpected ecological effects, these effects need to be clearly identified and monitored by qualified experts to make it easier to respond appropriately.

The current situation of species extinctions and diminishing numbers of mammals simply can’t be allowed to continue.  In Pope Francis’s words:

The idea of infinite or unlimited growth…is based on the lie that there is an infinite supply of the earth’s goods, and this leads to the planet being squeezed dry at every limit….Yet all is not lost. Human beings, while capable of the worst, are also capable of rising above themselves, choosing again what is good, and making a new start. (end of quote)

The decline of wild mammals that we have witnessed over the last century is yet another consequence of unchecked, selfish human behaviour squeezing the planet dry.  So let’s rise above ourselves, choose again what is good, and make a new start today to redress this decline and create a world where wild mammals and other creatures flourish, in natural, healthy, sustainable surroundings.





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