Britannica Student Encyclopedia - 2010

much greater numbers. Tens of millions

of American bison roamed the western

plains in what are now Canada and the

United States. They were important

animals to the Plains Indians. The European

bison once lived throughout most

of Europe. Over time settlers and hunters

killed millions of both types of bison.

By the early 1900s both species were

endangered, or in danger of dying out.

Since then people have worked to save

these animals.

Today the American bison is found

mainly in protected areas such as

national parks. It is no longer endangered.

Small numbers of European bison

can be found in parts of eastern Europe,

especially Poland, Belarus, Ukraine, and

Russia. It is still an endangered species.

Physical Features

Bison are large, powerful animals. An

adult male American bison stands about

6.5 feet (2 meters) tall at the shoulder. It

may weigh about 2,000 pounds (900

kilograms). The females are smaller. The

European bison is slightly larger than

the American bison but is not as heavily

built.

Bison have huge heads and a hump at

the shoulders. Two short horns curve

upward. They have hooves on all four

feet. Bison have shaggy brown fur. The

fur is usually longer on the head, neck,

and shoulders.

A herd of bison runs through a state park in

South Dakota.

American, or plains, bison

82 Bison BRITANNICA STUDENT ENCYCLOPEDIA

 

Behavior

Bison eat mainly grasses. They usually

move with a plodding walk. But they

can also run at speeds of about 40 miles

per hour (65 kilometers per hour). Bison

usually live in small groups. Sometimes

dozens or even hundreds of groups come

together to form large herds.

#More to explore

Buffalo • Cattle • Endangered Species

• Mammal • Yak

Bissau

Population

(2004 estimate)

305,700

Bissau is the capital of the West African

country of Guinea-Bissau. The city lies

on the Atlantic Ocean at the mouth of

the Geba River. It is the country’s

largest city and main port. Factories in

Bissau process coconuts, cashews, and

rice.

The Portuguese founded Bissau in 1687

as a fort and center for trading slaves.

Over the next 200 years several

European countries struggled for

control of the city and its port. Portugal

made all of what is now Guinea-Bissau

into a colony by 1915. Bissau became

the capital of the colony in 1941. In

1974 Guinea-Bissau became an

independent country. Bissau remained

its capital.

#More to explore

Guinea-Bissau

Bivalve

Bivalves are animals that have a shell

with two halves called valves. The word

bivalve means “two valves.” Bivalves are

part of a larger group called mollusks.

Mollusks are a type of animal with a soft

body.

There are about 8,000 species, or kinds,

of bivalve. They include scallops, cockles,

clams, oysters, and mussels. Most

bivalves live in the ocean, but a few species

live in freshwater.

Physical Features

Bivalves vary greatly in size, shape, and

color. Tiny freshwater shells may be only

0.06 inch (1.5 millimeters) long. Giant

clams in the southern Pacific Ocean may

be more than 4 feet (1.2 meters) long

Scallops are a type of bivalve. Most kinds

of scallop shells are shaped like fans.

BRITANNICA STUDENT ENCYCLOPEDIA Bivalve 83

 

and weigh more than 500 pounds (225

kilograms).

A bivalve’s shell protects its soft body.

Muscles connect the two valves of the

shell on one side. These muscles allow

the shell to close quickly and tightly.

When a bivalve relaxes the muscles, the

shell opens.

A bivalve’s body includes a nervous system,

a digestive system, and a heart.

Bivalves have gills instead of lungs.

When a bivalve opens its shell, water

washes over the gills. The gills then

strain out oxygen and food particles.

Behavior

Different bivalve species live in different

ways. Oysters and ocean mussels spend

their lives attached to solid, underwater

surfaces, such as rocks on the ocean

floor. Some bivalves, such as scallops,

swim by clapping their valves together.

This pushes water out of the shell and

moves them forward. Clams and freshwater

mussels move around with a muscular

“foot.” The foot is shaped like a

blade. These bivalves escape enemies by

using it to dig into sand.

Uses

Bivalves are an important source of food

for fish, birds, and people. People also

make jewelry and crafts out of the shells.

The shiny material of some shells, called

mother-of-pearl, can be made into buttons

or other decorations. Some bivalves

build shiny round beads around particles

of dirt that enter their shells.

People make jewelry out of these beads,

which are called pearls.

#More to explore

Mollusk • Shell

Black Americans

#see African Americans.

Blackbird

There are many species, or types, of

blackbird—songbirds named for the

black color of the males’ feathers. The

OldWorld, or common, blackbird is

related to thrushes, robins, and bluebirds.

All other types of blackbird are in

the same scientific family with grackles,

cowbirds, orioles, and meadowlarks. The

best-known types are the red-winged

blackbird and the yellow-headed blackbird.

Although crows and ravens also

have black feathers, those birds are not

called blackbirds.

Early humans

used scallop

shells as

dishes.

The red-winged blackbird is found in North

America and Central America.