The World Conservation Union has classified more than 700 species of animals worldwide as endangered—that is, faced with extinction unless humans provide direct protection, and another 800 as vulnerable, or threatened. Although some extinction is part of the natural ebb and flow of life on the planet, many human activities contribute to the dwindling numbers of many of the earth’s animals.
The existence of life on earth depends on a narrow range of acceptable conditions, and even small variations in such factors as rainfall, temperature range, or chemical pollution levels can lead to the extinction of a variety or a species of animal. And each extinction inevitably has some effect on all the local species, as the ecological balance readjusts to compensate and regain stability.
A larger climatic or other change can have even more dramatic effects. For example, there is strong evidence that the sudden and total disappearance about 65 million years ago of the dinosaurs (then the dominant life form) and many other species resulted from catastrophic climatic changes caused by a collision between the earth and an asteroid. Ice ages, which might have been caused by variations in the sun’s activity, had a dramatic effect on plants and animals, leading to the reduction or extinction of some species and the increase or evolution of other better adapted ones.
Effects of one species on another
The gradual evolution of better adapted life forms causes the reduction in numbers and possibly the eventual extinction of less well-adapted species trying to occupy the same ecological niche. In addition, groups of plant and animal species become interdependent in areas of reproduction, habitat, or food requirements. Any external event that affects the numbers or habits of one of these species may therefore have disastrous effects on the survival of the other dependent species. Such interdependence reduces the chances of survival of the species concerned. And disease particularly the evolution of new virus strains threatens certain species with extinction while leaving others relatively unaffected.
In each ecological environment one dominant species is likely to evolve, and it has a major influence on the ecological balance, affecting the numbers and survival of other species. The dominant species is most likely to be the predator at the top of the food chain. It will be challenged and replaced as the dominant species only by the evolution of a better adapted species, or by a physical change in the environment.
The activities of humans
The evolution of humans as an intelligent and highly adaptive species has led to a situation in which they have a position of dominance over all other species on earth. This fact, linked with the ability of humans to modify or even totally alter the environment, has placed many species in danger of extinction. Pressures of food production for a rapidly expanding human population have meant that there is probably no natural habitat that is not now threatened.
The threat of humankind to other species is apparent in a number of ways. The development of domesticated strains of plants and animals to improve the efficiency of food production (for example, wheat and domestic cattle) demands the creation of specialized environments that make large areas of habitat unavailable to the native plants and animals. Indeed, people take positive action to exclude the naturally occurring plants and animals from these areas with such weapons as weed-killers, insecticides, traps, and fences.
Increased requirements for living space for people remove land from the natural environment as new towns and cities are built. Relocation of waterways and the physical manipulation of the landscape further eliminate natural habitats. In addition, overgrazing of domestic animals can cause soil erosion, reducing previously fertile land to desert, again changing the local ecological balance.
The exploitation of a species for food, clothing, or ornament can reduce its numbers to below that necessary to maintain a population that can survive. Human activities such as farming and industry create pollution by releasing poisonous chemicals into the atmosphere, soil, and water. Species with little tolerance to such pollutants may be threatened. Sometimes catastrophic accidents that release large amounts of oil, toxic gases, or radioactive waste can have immediate and disastrous effects on wildlife. The burning of wood and fossil fuels to produce energy may have longterm effects on the carbon dioxide content of the atmosphere, possibly negatively affecting the climate. Other experiments in climate control might have unpredictable effects on the world’s ecology.
The deliberate or accidental introduction of species from different parts of the world into an ecology can have a disastrous effect on local species and may result in the extinction of those that are unable to compete or those that the new species prey upon.
Endangered lower animals
Increasingly, people are becoming aware that various species of birds and mammals are in danger of extinction. But many other animals, such as mollusks, insects, fishes, and reptiles, are also endangered. Colorful tropical butterflies are caught by the thousands so that their wings can be used in jewelry and ornaments. Some species of snails, crabs, and crayfish are caught and eaten as delicacies in restaurants throughout the world. Fishes continue to suffer from the effects of overfishing and pollution of the seas and oceans.
Nearly all such lower animals are part of the food supply of an interdependent chain of higher animals. Eventually, some birds and mammals also may become threatened as their food supply diminishes. And ultimately, the threat may extend to the food supplies of humans themselves.
The greatest of the threats to lower animals is pollution—from the testing of nuclear weapons to the dumping of sewage and industrial waste. For example, the Puerto Rican crested toad, the Virgin Islands boa, and the Aruba Island rattlesnake now exist on only a few islands because humans have claimed their natural habitats for tourism and agriculture. Their continued survival is dependent on reintroduction of zoo-born animals and careful management of protected areas.
An instructive example of the threat to lower animals in the sea is provided by the myriad array of fishes and other creatures that depend for their existence on Australia’s Great Barrier Reef. Since the 1960’s, some parts of the coral reef have died off as a result of pollution and a plague of large, dark, spiny starfish known as the crown-of-thorns. These starfish, often as many as 15 of them on each square yard or meter of reef, prey on coral-forming animals.
The large increase in the number of crown-of-thorns is due in part to the removal from the reef of their chief natural enemies—and population stabilizers—the large marine snails called tritons and helmet shells, whose ornamental shells were much prized by tourists. The sale of these shells has now been halted. If the snail population increases, it will keep the crown-of-thorns population in check, which will allow the coral to revive. Thus, a healthy balance of species will be restored to the reef.
Concentrated fishing and pollution has resulted in shortages in the world’s fish populations. Since the 1940’s, the fishing of some species has become so intensive that even common fishes such as flounders, ocean perch, lake herring, and tuna are presently in danger. Often the cause lies not merely in the huge amounts of fish that are caught, but in the fact that, by using nets with a very small mesh, fishers are catching immature fish before they have a chance to breed. Also, the sale of highly valued tropical fish for home aquariums has threatened some of these species.
Most of the major species of endangered lower animals on the land, and in its associated freshwater lakes and rivers, are reptiles. In the Americas, two tortoises, the Mexican gopher and the giant Galapagos land tortoise, are at risk, and the population of the Cuban crocodile has been estimated at fewer than 500 individuals. The short-necked tortoises of western Australia probably total only half that number. And on the small islands off the North Island of New Zealand, the unique, primitive, lizardlike animal called the tuatara the sole remaining species of a whole order of reptiles that has remained virtually unchanged for 20 million years is in danger of joining the dinosaurs in extinction.
Ever since the last dodo disappeared from the island of Mauritius in 1681, about 80 species of birds have become extinct. Today, there are about 210 species and subspecies in danger of extinction. The main threats are to large birds. They are conspicuous and easy to kill, and they breed slowly and thus cannot compensate for hunting or other unnatural mortality. Birds that are confined to islands are particularly at risk because they have small populations and often are not afraid of humans.
Various human activities directly threaten bird populations. The most obvious is hunting for food, feathers, or sport. Although a significant threat to birds in many parts of the world, uncontrolled hunting is declining in northern Europe and North America, with more enlightened attitudes about conservation. But controls have come too late for some species, such as the Eskimo curlew. Once seen in huge migratory flocks numbering thousands of birds, the Eskimo curlew has not been sighted for several years and may well be extinct.
The California condor is now extinct in the wild. One of the world’s heaviest flying species, with an 8-foot (2.4-meter) wingspan, this majestic vulture was once scarce but widespread over much of North America. The primary reason for its decline is land cultivation—it needs huge hunting areas in which to find animal carcasses—and the small population has been further depleted by illegal shooting. Another example of such a large, slow-breeding bird is the Steller’s, or shorttailed, albatross. Japanese plume traders have slaughtered millions of them, so that the albatross is now reduced to a small colony on Tor-ishima Island, near Japan.
To this day, hunting in areas such as the Mediterranean accounts for many thousands of birds killed. In Italy, for instance, about 100 million songbirds such as robins and thrushes are killed every year. Such pressures can result in local extinctions or near extinctions, as with the threatened European population of the great bustard or the extermination of the Arabian race of the ostrich in the 1960’s as a result of elaborate hunting expeditions. An indirect hazard of hunting is that birds eat the waste lead shot scattered over the ground from shotguns. Lead poisoning is a particular threat to swans, geese, and ducks.
Rare species are threatened by unscrupulous egg collectors and taxidermists. Illegal collecting of live birds for the pet trade is also a problem. Exotic tropical birds, particularly parrots, suffer most. Huge numbers are captured, and many die crammed in packing cases in aircraft.
Another direct threat occurs when birds are killed because they are thought, often wrongly, to be a pest. The only North American parrot, the Carolina parakeet, once was common, but by 1904 had been hunted to extinction because of its fondness for fruit, especially the citrus fruit in settlers’ orchards. Unfortunately, such orchards had replaced much of the birds’ original forest habitat.
The main damage to birds, however, is being done indirectly by habitat destruction or alteration and pollution. The most serious threats are to birds of tropical rain forests and wetlands. Logging has destroyed most of the habitat of the Cuban and American races of the ivory-billed woodpecker, for example, and for many years they were feared to be extinct. Although the American population is definitely extinct, in 1986 at least two ivory-billed woodpeckers were sighted in Cuba. However, it is doubtful that these birds represent a viable population. The diminutive Kirtland’s warbler struggles to survive in its extremely specialized habitat in central Michigan, helped by careful management and strict protection. There are about 1,000 of these small, yellowbreasted birds, which nest only in areas of forest that have been burned.
Wetland species such as the Japanese crane and the whooping crane are similarly threatened as drainage, pollution, and acid rain from factory emissions destroy their habitats. Oil pollution accounts for the deaths of countless thousands of seabirds and waterfowl.
Other indirect threats to seabirds include fishing nets. Danish fishing boats off Greenland are thought to have killed an estimated 500,000 Brunnich’s guillemots in their salmon nets.
Pesticides have had a devastating effect on many birds, such as the peregrine falcon. In the 1950’s, the peregrine was almost wiped out in North America and severely reduced in Europe because it ate prey that had been feeding on crops sprayed with DDT and other pesticides. Other birds that have suffered similarly include the American bald eagle, the osprey, various species of pelicans, and the bald ibis. However, with the ban on DDT in the 1960’s, these species have rebounded and the status of bald eagles has improved from endangered to threatened.
One of the worst of all indirect threats comes from animals introduced by humans, especially on islands where there are no indigenous mammalian predators. Cats, rats, dogs, and hogs have helped wipe out many species. Rats, for instance, have caused the extinction of at least nine species of flightless island rails, and cats introduced in 1931 to Herokapare Island, New Zealand, have wiped out six species and reduced the total bird population from an estimated 400,000 to a few thousand.
Almost every year for the past 80 years, at least one species of mammal has become extinct. Of the more than 4,500 or so living species of mammals, 475 are currently listed as endangered and are given protection by international law from hunting and exploitation.
Conspicuous and often posing physical competition or danger to humans, mammals are on the front line of the fight for survival. Humans have considerable commercial interest in mammals and depend on them for a variety of purposes. Whales are killed for their oil and meat, monkeys are snatched from forests for medical research, leopards and cheetahs are killed for sport and the profit from the sale of their fur. Other mammals—the giant panda and tiger, for example—are threatened by the destruction of their natural environments caused by concentrated exploitation of valued natural resources or through conversion of forest land for agriculture. The discharge of chemicals and liquid waste into lakes and rivers is another hazard.
Special parts of some mammals are sought by the fashion and jewelry trade. Rhinoceros horn is a highly prized ingredient in East Asian health potions and is carved into dagger handles in several African and Arabian countries Ambergris, a substance produced in the bodies of sperm whales, is used as a base for perfumes. Elephant and walrus ivory are prized for use in a variety of decorative objects and jewelry and was once used for piano keys. Crocodile skin is also in demand for shoes, belts, and other leather goods. Even when animals are protected by law, poachers will go to great lengths to obtain them.
The whale is a potent symbol of endangered aquatic mammals, and of the need for international management and regulation. In the 1800’s, the herds of whales that gathered in the plankton-rich waters of the Antarctic were extensively hunted and killed. Modern intensive hunting has left many species at the edge of extinction. A hundred years ago, the blue whale—the world’s largest mammal—numbered nearly 250,000. By 1965, a mere 2,000 were left, and some experts believe that the animal is now beyond saving. International concern over the blue whale caused Antarctic whalers to “mass hunt” smaller species. As a result, all of the eight species of whales are now in danger. The gray whale of the Pacific was near extinction earlier in this century. However, a ban on whaling has brought the population back to a nonendangered status. The humpback whale has been reduced to an estimated 1,000. Fin, sperm, sei, and minke whales are also threatened.
Other sea mammals are also protected. Restrictions on hunting have saved the polar bear and various species of seals. The Arctic fox is also given limited protection.
The fate of the European bison, the largest of Europe’s mammals, was determined by a high demand for the land over which they roamed. By the beginning of the twentieth century, the bison was almost extinct, as were the wolves and bears that occupied the same habitats. National parks throughout Europe now offer sanctuary not only to the bison but also to elk, deer, beaver, otter, and other mammals. Bears are protected in special reserves.
Once found over most of the northern half of the world, the wolf is now becoming scarce in many countries. It is rare in western Europe and extinct in 11 countries, killed for a variety of reasons, most often because farmers believed them to be a threat to their livestock. Once common in Europe and northern Asia, the European lynx is now scarce, although government protection is helping stabilize the population and there are plans to reintroduce animals bred in zoos.
The colonization of Africa over the last two centuries led to the over-hunting of many large mammals, and many species disappeared from their former ranges. Many populations declined as well, as forests were cut for agriculture and ranching. During the 1880’s, for example, nearly 80,000 elephants were killed for their ivory. But this total paled in comparison to the slaughter in the 1980’s and early 1990’s. Today, there is an international ban on trade in elephant ivory, and elephants are protected on many special reserves.
Many of Africa’s familiar mammals are now seriously at risk. A list of threatened African mammals includes the lemurs of Madagascar, the okapi, the mountain gorilla, Grevy’s zebra, the eland, and the black rhinoceros. These animals have been given complete protection, and the giraffe, chimpanzee, and some of the big cats—especially the cheetah—are guaranteed a limited safety. Poaching, however, still occurs in the large game reserves. The high price of rhino horn has driven the black rhino to a precariously small wild population of less than 3,000 individuals.
Animals of the Americas also face extinction, including the polar bear of northern North America, the brown grizzly bear of the Rocky Mountains, and the spectacled bear of the Andes. Other endangered American mammals include the black-footed ferret, Mexican pronghorn, mountain and Baird’s tapirs, Mexican wolf, pampas deer, chinchilla, and vicuna.
In Australia, the unique native marsupials are found nowhere else in the world, yet these same animals are being threatened by the spread of mechanized agriculture and the search for minerals. One mammal, the striped, wolflike Tasmanian tiger (also known as thy-lacine) is now thought by scientists to be extinct.
Despite the number of animal species that have become extinct, the conservation movement has had many successes. One achievement has been the establishment of national parks and reserves. An international conference in Paris in 1968 established that such parks should be at least about 1,920 acres (800 hectares) in extent, with strict prohibitions on mining, cultivation, stock raising, hunting, and fishing. There are now more than 1,400 reserves in the world, covering over 3 billion acres (1.25 billion hectares).
Many national parks in Africa offer protected sanctuary to rhinoceroses and other animals. Kruger Park in South Africa covers nearly 2.5 million acres (1 million hectares) and contains many different habitats, ranging from humid tropical forest to near desert, hot savanna to bamboo forests. Apart from animals such as the wildebeest, Kruger Park harbors groups of other animals, such as zorillas, that would otherwise be extinct.
European national parks and wilderness guarantee the conservation of several varieties of eagles and owls, the peregrine falcon, the rose flamingo, and other birds. The Camargue, a swampy wilderness in France, is one of many wetlands that has preserved a great number of the 150 species of migrating water birds. In Africa, similar sanctuaries have conserved the secretary bird, ostrich, maribou stork, pelican, and many small birds that migrate the length of the continent.
Australia has been very aggressive in protecting its native species. Special efforts are being made to preserve the koala, the platypus, and the echidna. More than 122 million acres (49 million hectares) of terrestrial Australian territory now lie within the boundaries of a number of national parks. Special task forces are charged with protecting and rehabilitating endangered species.
International maritime treaties have also been instrumental in preserving many species of the sea, including whales, fish, dolphins, and seals. CITES, the Convention on the Trade in Endangered Species, regulates trade in species between countries.
One particular animal conservation success story involves the preservation of the polar bear. In 1955, the International Union for the Conservation of Nature recommended that all Arctic countries should curb the hunting of bears. In 1965, the Soviet Union banned the killing of polar bears and established a special reserve for them on Wrangle Island. Norway has set up a similar sanctuary. In Canada, only licensed hunters and Inuit, sometimes called Eskimos, are permitted to hunt bears. Despite safari hunts outside territorial waters, the population of the animals has increased to the point that it is no longer classed as endangered.
The preservation of the oryx is another notable conservation success story. By 1960, there were less than 100 Arabian oryxes. Hunters using machine guns and jeeps eventually drove this species to extinction in the wild. However, three oryxes that had been captured in 1962 were bred successfully with other oryxes in captivity, thus saving the oryx from complete extinction. In the late 1980’s and early 1990’s, an international breeding effort among zoos in the United States and other countries returned the oryx to its natural habitat in Saudi Arabia and Oman.
Captive breeding programs also have been instrumental in conservation efforts on behalf of many other species, including black-footed ferrets, Mexican wolves, white rhinoceroses, golden lion tamarins, American and European bison, timber or gray wolves, swift foxes, and Przewalski’s horses.
In spite of these efforts, there are many endangered species whose populations are already so small that, even though some individuals are protected by reserves or in zoos, their future remains in doubt. For example, only about 60 Micronesian kingfishers remain, and all are in zoos. And less than 20 Hawaiian crows remain in the world in a captive facility in the wild. Many other species also exist only in zoos or at other captive breeding facilities. However, captive breeding is only one potential solution in the war against extinction. Efforts to preserve animal habitats must continue and must expand if many more species are to stave off extinction.