Endangered and Extinct Species 385Peter Yates/Science Sourcebetween 1900 and 1960 they disappeared from most of
their original geographic range. As a result of sharply
decreased numbers of prairie dogs, the black-footed
ferret, the natural predator of these animals, became
endangered. A successful captive-breeding program has
allowed black-footed ferrets to be reintroduced into the
wild and reproduce successfully, though some popula-
tions have been decimated by disease.
Unregulated hunting, or overhunting, was a factor
contributing to the extinction of certain species in the
past but is now strictly controlled in most countries. The
passenger pigeon was one of the most common birds
in North America in the early 1800s, but a century of
overhunting resulted in its extinction in the early 1900s.
Unregulated hunting was one of several factors that
caused the near extinction of the American bison.
Illegal commercial hunting, or poaching, endangers
many larger animals, such as the tiger, cheetah, and snow
leopard, whose beautiful furs are quite valuable. Rhinoc-
eroses are slaughtered primarily for their horns, used for
ceremonial dagger handles in the Middle East and for
purported medicinal purposes in Asian medicine. Bears
are killed for their gallbladders, used in Asian medicine to
treat ailments ranging from indigestion to heart problems.
Endangered American turtles are captured and exported
illegally to China, where they are killed for food. Caimans
(reptiles similar to crocodiles) are killed for their skins and
made into shoes and handbags. Although all these animals
are legally protected, the demand for their products on
the black market has led to their being hunted illegally.
In West Africa, poaching has contributed to the
decline in lowland gorilla and chimpanzee populations.
The meat (called bushmeat) of these rare primates and
other protected species, such as anteaters, elephants,
and mandrill baboons, provides an important source
of protein for indigenous people. Bushmeat is also sold
to urban restaurants. This demand for a meat source
increases the incidence of poaching.
Live organisms collected through commercial har-
vest end up in zoos, aquaria, biomedical research labo-
ratories, circuses, and pet stores. Several million birds
are commercially harvested each year for the pet trade,
but unfortunately many of them die in transit, and many
more die from improper treatment after they are in their
owners’ homes. Although it is illegal to capture endan-
gered animals from nature, there is a thriving black
market, mainly because collectors in the United States,
Canada, Europe, and Japan are willing to pay largemussels, and clams, threatening their survival. The U.S.
Coast Guard estimates that economic losses and control
efforts associated with the zebra mussel cost the United
States about $5 billion each year.
Two other examples further illustrate the harm
caused by invasive species. Two species of Asian carp were
introduced by aquaculture facilities flooding into the Mis-
sissippi River in the 1990s; they spread rapidly and now
threaten the multimillion dollar Great Lakes commercial
and sport fisheries. The Burmese python, released into
Florida’s Everglades National Park by pet owners (see
Chapter 6 opener), has multiplied and since 2000 has dec-
imated small mammal populations, essentially wiping out
some species there. Estimates of the number of non-native
species now in the United States vary widely, but there may
be as many as 50,000. Of these, approximately 4300 are
considered invasive species. Worldwide, most regions are
estimated to contain 10 to 30 percent foreign species.
Overexploitation Sometimes species become endan-
gered or extinct as a result of deliberate efforts to eradicate
or control their numbers. Many of these species prey on
game animals or livestock. Ranchers, hunters, and govern-
ment agents have reduced populations of large predators
such as wolves and grizzly bears. Some animals are killed
because they cause problems for humans. The Carolina
parakeet, a beautiful green, red, and yellow bird endemic
to the southern United States, was extinct by 1920, exter-
minated by farmers because it ate fruit and grain crops.
Prairie dogs and pocket gophers were poisoned
and trapped so extensively by ranchers and farmers that
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Zebra mussels, here clogging a section of water pipe, have
caused billions of dollars in damage, in addition to displacing
native clams and mussels.