An endangered species is a plant, animal or other organism that is threatened by extinction. Species become endangered for two main reasons: loss of habitat and loss of genetic variation.

 
Loss Of Habitat
 
A loss of habitat can happen naturally. Dinosaurs, for instance, lost their habitat about 65 million years ago. The hot, dry climate of the Cretaceous period changed very quickly, most likely because of an asteroid striking the Earth. The impact blasted debris into the atmosphere, reducing the amount of heat and light that reached Earth's surface. The dinosaurs were unable to adapt to this new, cooler habitat. They eventually became extinct.


 
Human activity can also contribute to a loss of habitat. Development for housing, industry, and agriculture reduces the habitat of native organisms. 
 
Development can eliminate habitat and native species directly. In the Amazon rain forest of South America, for example, developers have cleared hundreds of thousands of acres. To "clear" a piece of land is to remove all trees and vegetation from it. The Amazon rain forest is cleared for cattle ranches, logging, and urban use. 


 
Development can also endanger species indirectly. Some species, such as fig trees of the rain forest, may provide habitat for other species. As trees are destroyed, species that depend on that tree may also become endangered. Trees provide habitat in the canopy, or top layer, of a rain forest. Plants such as vines, fungi such as mushrooms and insects such as butterflies live in the rain forest canopy. So do hundreds of species of tropical birds and mammals such as monkeys. As trees are cut down, this habitat is lost. Species have less room to live and reproduce.


 
Loss Of Genetic Variation
 
Genetic variation is the diversity found within a species. It's why human beings may have blond, red, brown or black hair. Genetic variation allows species to adapt to changes in the environment. Usually, the greater the population of a species, the greater its genetic variation. 


 
Inbreeding is when close family members reproduce. Groups of species that inbreed usually have less genetic variation, because no new genetic information is introduced to the group. Disease is much more common, and much more deadly, among inbred groups. Inbred species do not have the genetic variation to develop resistance to the disease. For this reason, fewer offspring of inbred groups survive to maturity.


 
Loss of genetic variation can occur naturally. Cheetahs are a threatened species native to Africa and Asia. These big cats have very little genetic variation. They cannot adapt to changes in the environment as quickly as other animals, and fewer cheetahs survive to maturity. 
 
Human activity can also lead to a loss of genetic variation. Overhunting and overfishing have reduced the populations of many animals. Reduced population usually means there is less genetic variation.
 
 
The International Union for Conservation of Nature (IUCN) keeps a "Red List of Threatened Species." The list alerts organizations and governments about species that require greater conservation efforts. 
 
The Red List defines the seriousness and causes of a species' risk of extinction. The threat is usually calculated by the size of a population, or if the population has experienced a sudden sharp decline. Rapid destruction of its habitat is also an important factor.
 
The Red List has seven levels of conservation: least concern, near threatened, vulnerable, endangered, critically endangered, extinct in the wild and extinct. Each category represents a different threat level. 


 
Least Concern And Near Threatened
 
Least concern is the lowest level of conservation. A species of least concern is one that has a widespread and abundant population. Human beings are a species of least concern, for example, along with most domestic animals, such as dogs and cats. Many wild animals, such as pigeons and houseflies, are also classified as least concern.


 
A near threatened species is one that may face a significant threat in the near future. 

Many species of violets, native to tropical jungles in South America and Africa, are near threatened, for instance. They have healthy populations. However, their habitat is disappearing at a fast pace. 
 
Vulnerable, Endangered And Critically Endangered Species
 
These three categories — vulnerable, endangered and critically endangered — include species facing potential threats. As their population and habitat decreases, these species become more threatened.


 
Vulnerable Species: Ethiopian Banana Frog

 
This small frog is native to southern Ethiopia in Africa. It is a vulnerable species because the size and quality of its forest habitat are in decline. 
 
Endangered Species: Siberian Sturgeon
 
The Siberian sturgeon is a large fish found in rivers and lakes of eastern Russia. It is endangered because it has lost more than half its total population in the past 60 years. Overfishing, pollution and dam construction have contributed to this decline. 
 
Critically Endangered Species: Bolivian Chinchilla Rat

 
The Bolivian chinchilla rat is a rodent found in a small part of Bolivia, in South America. It is critically endangered because its habitat has shrunk to less than 100 square kilometers (39 square miles). 

The major threat to this species is loss of its forest habitat.
 
Extinct In The Wild And Extinct
 
A species is extinct in the wild when it no longer lives in its natural habitat. However, it may survive in zoos (animals) or be cultivated in greenhouses (plants). A species is extinct when the last individual of that species has died. 


 
Extinct in the Wild: Black Soft-shell Turtle
 
The black soft-shell turtle is a freshwater turtle. It exists only in one man-made pond in Bangladesh. The 150 to 300 turtles that live at the pond rely entirely on humans for food. 
 
Extinct: Cuban Macaw
 
The Cuban macaw was a tropical parrot native to Cuba. Hunting and collecting the birds for pets led to the bird's extinction in the 1800s.
 
Protecting Endangered Species
 
When a species is classified as endangered, governments and international organizations can work to protect it. Laws may limit hunting and destruction of the species' habitat. Individuals and companies that break these laws may face huge fines. Because of such actions, many species have recovered from their endangered status.
 
The brown pelican was taken off the endangered species list in 2009, for instance. This seabird is native to the coasts of North America and South America, as well as the islands of the Caribbean Sea. In 1970, the number of brown pelicans in the wild was estimated at 10,000. The bird was classified as vulnerable.


 
During the 1970s and 1980s, governments and conservation groups worked to help the brown pelican recover. Young chicks were reared in hatching sites, then released into the wild. The pesticide DDT, which damaged the eggs of the brown pelican, was banned. During the 1980s, the number of brown pelicans soared. The bird, whose population is now in the hundreds of thousands, has been moved to the category of least concern. Today, it is considered safe from extinction, thanks to the efforts of people who worked to save it.
 
endangered species
Unlike many endangered species, there are still more giant pandas in the wild than there are in zoos.
abnormality
Noun

deformity or condition different from the normal or expected state of being.

abundant
Adjective

in large amounts.

adapt
Verb

to adjust to new surroundings or a new situation.

agribusiness
Noun

the strategy of applying profit-making practices to the operation of farms and ranches.

Noun

the art and science of cultivating land for growing crops (farming) or raising livestock (ranching).

Noun

the distance above sea level.

antelope
Noun

grazing mammal.

Noun

science of the origin, development, and culture of human beings.

area of occupancy
Noun

geographic area where a specific population of a species resides, used to determine a species' level of conservation.

asteroid
Noun

irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.

Noun

layers of gases surrounding a planet or other celestial body.

bamboo
Noun

type of huge, woody grass.

ban
Verb

to prohibit or not allow.

benthic
Adjective

having to do with the bottom of a deep body of water.

big cat
Noun

large predators, including tigers, lions, jaguars, and leopards.

biologist
Noun

scientist who studies living organisms.

botanical garden
Noun

place where plants and flowers are grown and displayed for education and study.

breed in captivity
Verb

to mate animals in a controlled environment.

breeding pair
Noun

animals who cooperate over a period of time to produce generations of offspring.

calculate
Verb

to reach a conclusion by mathematical or logical methods.

canopy
Noun

one of the top layers of a forest, formed by the thick leaves of very tall trees.

cattle pasture
Noun

large area of grassland where cattle graze.

cattle ranch
Noun

large farm where cattle are raised and bred for meat or leather.

cheetah
Noun

large, spotted cat native to Africa.

chess
Noun

game of strategy played by two players, each with 16 pieces moved across a checkered board.

chinchilla
Noun

rodent native to South America.

classify
Verb

to identify or arrange by specific type or characteristic.

climate
Noun

all weather conditions for a given location over a period of time.

Noun

gradual changes in all the interconnected weather elements on our planet.

cloud forest
Noun

wooded area, usually high-altitude, almost always covered by clouds and fog.

Noun

edge of land along the sea or other large body of water.

Noun

management of a natural resource to prevent exploitation, destruction, or neglect.

Convention on Biological Diversity
Noun

international treaty to sustain and protect the diversity of life on Earth.

Cretaceous period
Noun

145 million to 65 million years ago. The period ended with extinction of the dinosaurs and the rise of mammals.

critically endangered
Noun

level of conservation between "endangered" and "extinct in the wild."

Noun

agricultural produce.

cultivate
Verb

to encourage the growth of something through work and attention.

cyanea
Noun

type of plant native to Hawaii with large, broad leaves.

dam
Noun

structure built across a river or other waterway to control the flow of water.

DDT
Noun

(dichloro-diphenyl-trichloroethane) toxic chemical used as an insecticide but illegal for most uses in the U.S. since 1972.

debris
Noun

remains of something broken or destroyed; waste, or garbage.

decline
Verb

to reduce or go down in number.

descendant
Noun

children, grandchildren, and other offspring.

development
Noun

construction or preparation of land for housing, industry, or agriculture.

dinosaur
Noun

very large, extinct reptile chiefly from the Mesozoic Era, 251 million to 65 million years ago.

Noun

difference.

domestic animal
Noun

animal that has been tamed for work or to be a pet.

dwarf
Verb

to make something appear small by having it appear next to something much larger.

ebony
Noun

tree native to Africa that produces dark, hard timber.

eliminate
Verb

to remove.

Noun

irregular, recurring weather system that features a warm, eastern-flowing ocean current in the eastern Pacific Ocean.

encounter
Verb

to meet, especially unexpectedly.

Noun

organism threatened with extinction.

enormous
Adjective

very large.

extent of occurrence
Noun

smallest area that could contain all the sites of a species' population, used to determine a species level of conservation.

extinct
Adjective

no longer existing.

extinct in the wild
Noun

highest level of conservation of a living species, when the only living members of that species are protected in captivity such as zoos or aquariums.

Noun

process of complete disappearance of a species from Earth.

farm
Noun

land cultivated for crops, livestock, or both.

fertilizer
Noun

nutrient-rich chemical substance (natural or manmade) applied to soil to encourage plant growth.

fine
Verb

to punish, usually by charging an economic penalty or fee. Or, the penalty or fee itself.

fingerboard
Noun

flat part of a stringed instrument where the musician presses the string down to create a note.

fishery
Noun

industry or occupation of harvesting fish, either in the wild or through aquaculture.

frequent
Adjective

often.

fungi
Plural Noun

(singular: fungus) organisms that survive by decomposing and absorbing nutrients in organic material such as soil or dead organisms.

generation
Noun

group in a species made up of members that are roughly the same age.

Noun

differences in the genes among individual members of a species.

gourmet
Adjective

high-quality, expensive, or difficult-to-prepare food.

Noun

environment where an organism lives throughout the year or for shorter periods of time.

hatch
Verb

to emerge from an egg.

hippopotamus
Noun

large mammal native to Africa that lives near rivers.

ice age
Noun

long period of cold climate where glaciers cover large parts of the Earth. The last ice age peaked about 20,000 years ago. Also called glacial age.

impact
Noun

collision or crash.

inbreed
Verb

to produce offspring with close family members.

industry
Noun

activity that produces goods and services.

Noun

unit made up of governments or groups in different countries, usually for a specific purpose.

International Union for the Conservation of Nature (IUCN)
Noun

environmental organization concerned with preserving natural ecosystems and habitats.

Noun

type of plant or animal that is not indigenous to a particular area and causes economic or environmental harm.

Noun

body of land surrounded by water.

jungle
Noun

tropical ecosystem filled with trees and underbrush.

kelp
Noun

type of seaweed.

least concern
Adjective

lowest level of conservation, used when the population and habitat of a species are healthy.

legume
Noun

type of plant with a pod that splits, with seeds in the middle, such as peanuts.

level of conservation
Noun

one of seven categories of a species' threat of extinction, assigned by the International Union for the Conservation of Nature: least concern, near threatened, vulnerable, endangered, critically endangered, extinct in the wild, and extinct.

livestock
Noun

animals raised for human use.

logging
Noun

industry engaged in cutting down trees and moving the wood to sawmills.

Lonesome George
Noun

last surviving Pinta Island tortoise.

macaw
Noun

long-tailed parrot native to the Americas.

marble
Noun

type of metamorphic rock.

mature
Adjective

adult member of a species who is able to reproduce.

meteorologist
Noun

person who studies patterns and changes in Earth's atmosphere.

Noun

process of extracting ore from the Earth.

monitor
Verb

to observe and record behavior or data.

monoculture
Noun

the system of growing one type of crop.

mountain lion
Noun

large cat native to North and South America. Also called a cougar, puma, catamount, and panther.

mountain range
Noun

series or chain of mountains that are close together.

near threatened
Noun

level of conservation between "least concern" and "vulnerable."

nesting site
Noun

place where birds build nests and raise their young.

non-native species
Noun

a type of plant or animal that is not indigenous to a particular area. Non-native species can sometimes cause economic or environmental harm as an invasive species.

offspring
Noun

the children of a person or animal.

oryx
Noun

antelope native to Africa.

overfish
Verb

to harvest aquatic life to the point where species become rare in the area.

overharvest
Verb

to use more of a resource than can be replaced naturally.

overhunt
Verb

to capture and kill enough animals to reduce their breeding population below sustainable levels.

parrot
Noun

type of bird with a large beak.

patrol
Verb

to survey and monitor an area by passing through it.

pelican
Noun

large marine bird with a big bill.

pesticide
Noun

natural or manufactured substance used to kill organisms that threaten agriculture or are undesirable. Pesticides can be fungicides (which kill harmful fungi), insecticides (which kill harmful insects), herbicides (which kill harmful plants), or rodenticides (which kill harmful rodents.)

pet
Noun

animal kept as a helper or companion.

piano key
Noun

lever, either black or white, which triggers a hammer to hit a specific string inside the body of a piano.

Noun

large region that is higher than the surrounding area and relatively flat.

poach
Verb

to hunt, trap, or fish illegally.

poisonous
Adjective

toxic or containing dangerous chemicals.

Noun

introduction of harmful materials into the environment.

population reduction rate
Noun

rate at which the numbers of a specific species are shrinking.

population restrictions
Noun

calculation of a species' population and its area of occupancy that helps determine its conservation status.

probability of extinction
Noun

calculation of how long a species can survive without human protection.

racerunner
Noun

small lizard.

Noun

area of tall, mostly evergreen trees and a high amount of rainfall.

ratify
Verb

to formally approve or confirm.

Red List
Noun

list defining the severity and causes of each species' threat of extinction. The Red List is maintained by the International Union for the Conservation of Nature (IUCN).

reduce
Verb

to lower or lessen.

reproduce
Verb

to create offspring, by sexual or asexual means.

reproductive system
Noun

organs involved in an organism's reproduction.

rodent
Noun

order of mammals often characterized by long teeth for gnawing and nibbling.

Russet Burbank
Noun

large, brown-skinned potato often used for making french fries in fast food restaurants.

salination
Noun

process where soils build up high salt content.

scimitar
Noun

long, curved sword with a sharp outer edge, developed in the Middle East.

seabird
Noun

bird native to an aquatic environment.

seaweed
Noun

marine algae. Seaweed can be composed of brown, green, or red algae, as well as "blue-green algae," which is actually bacteria.

seep
Verb

to slowly flow through a border.

severe
Adjective

harsh.

shrine
Noun

place of worship or spiritual devotion.

soil
Noun

top layer of the Earth's surface where plants can grow.

songbird
Noun

bird with a recognizable vocal pattern.

Noun

native, geographic area in which an organism can be found. Range also refers to the geographic distribution of a particular species.

specimen
Noun

individual organism that is a typical example of its classification.

sturgeon
Noun

type of marine or freshwater large, long, bony fish.

Noun

use of resources in such a manner that they will never be exhausted.

tendency
Noun

habit or predictable way of behaving.

threatened categories
Noun

three levels of endangered species: vulnerable, endangered, and critically endangered.

threatened species
Noun

organism that may soon become endangered.

threshold
Noun

point in a process that must be met to start a new stage in the process.

timber
Noun

wood in an unfinished form, either trees or logs.

tortoise
Noun

land-based turtle, usually with a tall, rounded shell.

tree crown
Noun

top branches of a tree.

tropical
Adjective

existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.

turtle
Noun

type of reptile with a shell encasing most of its body.

Noun

developed, densely populated area where most inhabitants have nonagricultural jobs.

vegetation
Noun

all the plant life of a specific place.

violet
Noun

plant with small flowers.

virus
Noun

pathogenic agent that lives and multiplies in a living cell.

vulnerable species
Noun

level of conservation between "near threatened" and "endangered." Vulnerable is the lowest of the "threatened" categories.

warbler
Noun

type of small songbird.

weather pattern
Noun

repeating or predictable changes in the Earth's atmosphere, such as winds, precipitation, and temperatures.

weed
Noun

unwanted plant.

Noun

area of land covered by shallow water or saturated by water.

Noun

place where animals are kept for exhibition.