July 27, 2018 Endangered Species Written by Greentumble Editorial Team
reasons why animals become endangered
The United States Endangered Species Act

sums up the problem succinctly: The Congress finds and declares that (1) various species of fish, wildlife, and plants in the United States have been rendered extinct as a consequence of economic growth and development untempered by adequate concern and conservation [and] (2) other species of fish, wildlife, and plants have been so depleted in numbers that they are in danger of or threatened with extinction.

What is endangered species?

Basically, “endangered” means that a species is in danger of extinction throughout all or a significant portion of its range. 

Internationally, the IUCN Red List of Threatened Species is the most well-recognized catalog of threatened species. The list and ranking are prepared by the International Union for Conservation of Nature based on very specific criteria. Although the criteria is specific, the information it seeks is not usually as definable as finding and counting species is a problematic venture for many reasons.

Generally speaking, the criteria for “endangered” are:

  • a very significant reduction in population size of a large percentage over recent years
  • a continuing decline
  • a severely shrinking geographic range

Experts estimate that the extinction rate of animal species today is between 1,000 and 10,000 times higher than the natural extinction rate, that is what the extinction rate would be without human encroachment and activity [1].

It is estimated that today 50 percent of the world’s species are at risk of extinction [2].


What will lead to a species becoming endangered?

When there are very few animals left within a range where they can safely mate with other animals and raise offspring, and there is no habitat containing a large number of those same animals, their species is in danger of extinction.


What causes animals to become endangered?

Conservation biologists recognize that multiple forces drawn along with human activity reinforce one another to cause a species to diminish. 

They use the acronym HIPPO for Habitat destruction, Invasive species, Pollution, Population and Overharvesting [3].

The general consensus is that it is the P for people that is the primary cause of the dramatic declines in species worldwide. The bottom line is that we have too many people consuming too much of the land and sea and the earth’s resources.

#1 Overhunting or overharvesting

This has been the fate of most large animals, slow animals and tasty animals when humans have migrated to a previously uninhabited area. 

History abounds with stories of mass extinctions of animals by hunters and the consequent deaths of their predators if not by direct hunting as well, then by starvation because they no longer have a food source.

And a long history it is… There are many historical accounts about how humans have over hunted and over harvested species, leading to their endangerment, and often, extinction. The Passenger Pigeon is a classic example of how humans over hunted a species, leading to the extinction of the entire species.

A recent study suggests that the reason for the mass extinction of large mammals like mammoths, mastodons, and camels in the Americas between 13,300 and 15,000 years ago was because today humans hunted them into extinction [4].

It is the cause of some high profile near extinctions today, like elephants for their ivory tusks and rhinos for their horn. The horn is sold at exorbitant prices as cures from everything from hangovers to cancer.

Rhinos are hunted down for their horns.

Rhinos are hunted down for their horns.

The black rhino population was at 65,000 in 1970, but then an odd phenomenon occurred. The rise of oil prices due to the OPEC oil embargo made a lot of theretofore impoverished Yemenis very wealthy. 

Ceremonial daggers are bestowed upon young Yemeni males as a rite of passage and the most prized ones were made of black rhino horn, wildly driving the price up and the population of black rhinos down. 

By 1997, when Yemen at last became a party to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), only 2400 black rhinos remained, leaving the species on the brink of extinction [5]

The most poached animals in the world today are the small, shy pangolins. 100,000 are poached each year for their meat, considered a delicacy on Vietnam and China and their scales, believed to have healing powers [7].

Read more about the sad story of pangolins: Why Are Pangolins Endangered and The Most Poached Animals in the World

Plant species can also be overharvested, leading to their endangerment. For example, the Goldenseal plant is a very popular medicinal plant in the United States that has now become threatened due to overharvesting in the wild.

#2 Habitat loss

This is one of the biggest reasons for the steep decline of species, both in the animal world and the plant world. Many species in our world today are becoming endangered due to a loss of their primary habitat.  

Deforestation, agricultural spread, water extraction, mining and human migration have either destroyed the only habitats the species can survive in or driven the species to a severely fragmented habitat, generally meaning simply a slower demise of the species.

#3 Highly specialized species

Rarity has its own problems. Highly specialized species that have very specific habitat requirements do not fare well when faced with a changing environment, such as a changing climate or a habitat loss.

A small or very local population only has problems due to lack of suitable mates, and inbreeding presents another set of problems. The higher the level of inbreeding the double the dose of defective genes are passed on, generally leading to sterility and early death.

Too, a small population is especially vulnerable to the vagaries of Mother Nature. A single strong storm, flood, wildfire or drought can be a death knell to a species.

Deforestation is shrinking the habitat of red pandas.

Deforestation is shrinking the habitat of red pandas.

While some species have become well adapted to human presence (e.g. the Norway Rat), some species are so specialized that changes in their environment may threaten their very survival.

#4 Pollution

The Declining Amphibian Phenomenon is one of the more obvious measures of the declining state of our biosphere due to pollution. 

In Minnesota, many of the amphibians have extra legs or missing limbs due to birth defects from exposure to chemicals sprayed in the water to kill mosquitoes.

Although biologists have been unable to isolate a single cause for the recent rapid decline in numbers and extinctions of many species, it appears that much of it is due to pollution.

For example, the Peregrine Falcon almost became extinct in Canada when DDT was widely used prior to becoming banned in the U.S. and Canada in 1971. 

In the Sierra Nevada, cell damage due to excessive ultraviolet-B radiation, too strong with the thinning of the ozone layer. 

#5 New species introduction and competition

Invasive species are a major cause of loss of diversity of both plants and animals. When a new species arrives with no natural predators to keep it in check, it can take over

A familiar example is the brown tree snake inadvertently arriving in Guam on a cargo ship following WWII. The venomous brown snake has decimated on virtually all of the local bird, fruit bat and lizard populations [8].

Trout and bullfrogs introduced into streams are blamed for some of the amphibian dieoff.

And one other example happened in the Great Lakes region of the United States, where the Zebra Mussel was accidentally introduced. Many of the native mussel species in the Great Lakes have now become threatened or endangered due to the presence of the highly competitive Zebra Mussel.

#6 Human-wildlife conflict

“If it moves, kill it.”

Is pretty much the mentality in rural America. And yet in a surprising twist, Los Angeles, a city and its suburbs home to 19 million people is an enclave where mountain lions live side-by-side with humans [9].

Mountain lions have been roaming the city for at least 30 years and The National Park Service has been studying them since 2002, curious how mountain lions survive in an increasingly fragmented and urbanized landscape [10].

A recent citing prompted this response from a 65-year old resident. “I was stunned and amazed at the beauty. I didn’t feel scared, it didn’t seem like it was aggressive,” said Moore, who was returning from checking on her neighbor’s small Yorkie while she was out of town. “We just had a kind of staring contest and I didn’t want to take off and have it chase me or something.”

On the other hand, as our populations increase and more people move into areas where wildlife previously lived in abundance, new human-wildlife conflicts arise. Sadly, in many cases, wildlife is killed when they cause too big harm to farmers by hunting livestock or destroying crops.

Deer crossing the road.

Deer crossing the road, often resulting in animal being hurt.

For wildlife populations that have already been reduced due to loss of habitat and other issues, such conflicts can increase the chances that a species will become threatened or endangered.

#7 Disease

Diseases kill humans and animals alike. The Ebola virus killed 5000 critically endangered western gorillas between 2002 and 2003 at the Lossi Sanctuary and other hundreds of gorillas in the Odzala-Kokoua National Park in 2003-2004 [12].

A deadly fungus decimated 30 species of amphibians in Panama in the early 2000s

A deadly fungus from Europe, where it is harmless to bats has spread to North America killing 6 million bats and taking many species to the brink of extinction. The northern long-eared bat is believed to have declined by 99 percent due to the “white nose syndrome [13].”

It was a fungus that destroyed the American chestnut tree, one hundred-foot hardwoods that once numbered in the billions in eastern forests of the United States, and a significant food source for a variety of wildlife, but which were virtually eliminated by a fungal pathogen accidentally imported into the United States from Asia [14].

Because the American Chestnut tree had evolved in conditions without the presence of the fungus, it lacked the natural resistance to survive.

Currently, there is ongoing research with the aim of creating a hybrid chestnut variety that is a cross between the American Chestnut and a variety of Chinese chestnut that is resistant to the chestnut fungus.

#8 Low birth rate

It is believed that reproduction rates are a natural way of maintaining a population equilibrium. Some species do not reproduce very often, and they may have few offspring each time when they breed. Other species may take a number of years to become sexually mature, thus reducing their opportunity to breed over their lifetime.

Generally, larger mammals have longer lifetimes and lower birth rates and smaller animals like rodents who do not live as long produce many litters in succession [15].

Female pandas ovulate only once a year, in the spring for only a short period of two to four days on average – which is the only time she is able to conceive [16].

Consequently, when large mammals suffer man-induced mortality, it takes longer for their populations to recover. A good example are marine mammals whose populations were diminished by commercial exploration.

#9 High genetic vulnerability

If a population has low genetic variation, it cannot evolve on the face of changing environmental variables and will face an increased risk of extinction. 

For example, if a population does not have a gene that is resistant to a certain disease, that disease may wipe out the entire population in one fell stroke [17].

Some species, such as the Cheetah, maintain low genetic diversity, which makes them less able to adapt when faced with challenges such as overhunting or habitat loss. This low genetic diversity also makes them more vulnerable to diseases and expressions of negative genetic mutations.

Cheetah populations are vulnerable to diseases and sudden changes of their environment.

Cheetah populations are vulnerable to diseases and sudden changes of their environment.

Koalas are known to have low genetic variation [18]. This may be why they are showing high vulnerability to Chlamydia and the koala retrofit virus. Their vulnerability may also make it more difficult for koalas to adapt to global warming and human encroachment of their habitats.

#10 A particular species is rare to begin with

Some species can be found only in certain areas. If there are only a limited number of individuals of a species that are in existence to begin with, and the environment changes, there is a lower probability that such a species will survive in the future.

Rare species can easily become extinct in the face of hunting. The Sumatran Tiger is an example of a rare species that was over hunted to the point of extinction, as there were a very limited number of individuals to begin with.

There are only 1,000 ili pika, a tiny mammal living in a remote mountain range in China. Rising temperatures have forced them to the mountain tops. It is believed that the air pollution of the Xinjiang region has contributed to their decline. Removal from their habitat, vulnerability to pollution, and vulnerability to predators as they are too quiet by nature to warn each other makes their survival as a species unlikely [19].

What efforts are being taken to protect endangered wildlife?

Internationally, 199 countries have signed an accord to create Biodiversity Action Plans to address the conservation of threatened species and habitats [20].

CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora) is an international agreement between governments. Its aim is to ensure that international trade in specimens of wild animals and plants does not threaten their survival [21].

Many worthwhile organizations also exist to protect endangered species [22].

Efforts are made to find and rescue animals on the brink of extinction, bring them back to health, allow them to breed and raise their young in safe places, create a sustainable habitat and protect the habitat from encroachment, helping the animals along until they reach numbers that give them a fighting chance of survival as a species.

You can help too.


Find out from our article: Easy Things You Can Do to Save Endangered Wildlife.



[1] http://wwf.panda.org/our_work/biodiversity/biodiversity/
[2] https://web.archive.org/web/20120913043721/http:/www.conservationandwildlife.com/threatened-species
[3] https://www.e-education.psu.edu/geog30/node/394
[4] https://motherboard.vice.com/en_us/article/78kzke/new-evidence-suggests-early-humans-hunted-large-mammals-into-extinction
[5] The Future of Life, Wilson, Edward O., A.A.Knopf, NY 2002, p.86.
[6] https://www.savetherhino.org/rhino-species/black-rhino/western-black-rhino-declared-extinct-in-2011-journalists-reporting-news-two-years-later/
[7] https://greentumble.com/the-most-poached-animals-in-the-world/
[8] https://www.britannica.com/animal/brown-tree-snake
[9] https://www.cbsnews.com/pictures/60-minutes-mountain-lions-photo-gallery/
[10] https://www.nps.gov/samo/learn/nature/pumapage.htm
[11] http://www.latimes.com/local/lanow/la-me-ln-mountain-lion-azusa-20180326-story.html#
[12] http://www.bbc.com/earth/story/20150327-ten-scary-diseases-of-animals
[13] http://www.bbc.com/earth/story/20150327-ten-scary-diseases-of-animals
[14] https://www.acf.org/the-american-chestnut/
[15] https://www.mammalogy.org/uploads/committee_files/Why%20species%20become%20threatened%20or%20endangered%20brochure.pdf
[16] http://askascientist.co.uk/biology/pandas-low-birth-rate/
[17] https://evolution.berkeley.edu/evolibrary/article/conservation_04
[18] https://www.sciencedaily.com/releases/2012/10/121023204636.htm
[19] https://haydensanimalfacts.com/2015/04/30/5-interesting-facts-about-ili-pikas/
[20] https://www.sciencedaily.com/terms/biodiversity_action_plan.htm
[21] http://cites-dashboards.unep-wcmc.org/
[22] https://www.gviusa.com/blog/10-best-organisations-to-follow-help-endangered-animals/