International

Migratory Bird

Day (IMBD),

held annually

on the second

Saturday in

May, is an

invitation to

celebrate and

support

migratory bird

conservation.

IMBD Information

web http://birds.fws.gov/imbd.html

phone 703/358-2318

IMBD Sales

web http://www.BirdDay.org

phone 1-866/334-3330

January 2002

The Four Essential Elements

of Habitat

Food, Water, Cover, Space

Critical for Survival

All species of plants and animals—

including people—need a proper

combination of food, water, cover, and

space to survive and reproduce.

Together, these elements make up a

“habitat.” Without habitat, a species

cannot survive.

Since bird species are wonderfully

diverse in their forms and lifestyles, their

habitats vary tremendously. However,

regardless of location, be it sandy

seashore, tropical forest, arid grassland,

or urban neighborhood, a habitat must

fulfill the four essential needs.

• Food. Some species of birds are

herbivores, eating seeds, fruits, buds, or

flowers. Some are carnivores, eating

insects, snails, fish, other birds, or

carrion. Many species are omnivores,

eating both plant and animal matter. A

bird’s bill shape and size offer excellent

clues to the bird’s diet.

The type of food that a bird selects

depends on availability, and during

periods of abundance (for example,

during a spring fish spawning or fall

fruiting) its diet may become very

repetitive. A bird’s diet also depends on

its nutritional requirements,

which change with

season and age.

Breeding adults and

developing chicks

need additional

protein, for example.

Birds that eat plant

matter much of the

year, such as the

American Tree

Sparrow, will turn

to insects to fulfill

that need. Birds

undertaking

strenuous

migrations will

increase and alter their diets prior to

their journeys in order to accumulate

large amounts of energy in the form of

fat. As an extreme example, the

Blackpoll Warbler doubles its body

weight prior to migration!

• Water. Birds, like all living things,

require water. Most birds obtain water

by drinking—dipping with their bills and

tipping their heads back to swallow.

Pelicans have been seen standing with

their mouths open in the rain. Sea-going

birds, such as albatross, can drink

saltwater because of specialized nasal

glands that extract excess salt from the

blood. However, species with very moist

diets,such as hummingbirds and other

nectar-feeders, obtain water almost

completely from their food, and in very

arid regions, some species also rely on

metabolic water, produced as their bodies

burn fat.

Water can also be essential as a medium

for feeding and other activities. Herons

wade, puffins dive, ducks dabble, and

gulls skim the water in search of aquatic

foods. Many birds stay on the water to

rest, court, and preen. In fact, pelagic

(oceanic) species spend most of their time

out at sea, returning to land only to nest.
• Cover. Birds, nestlings in particular,

need shelter from predators and the

elements. Cover, including trees,

grasses, and rocks, also harbors foods for

birds and provides space or materials for

nesting. The requirements for cover can

be quite specific. Species often show a

marked preference for nesting and

foraging at certain heights and in certain

structures of vegetation. Cavity nesters,

such as woodpeckers, require trees of

the age and size to support suitable holes.

A bird’s needs may also change over

time. Open meadows and grasslands

provide good cover for wild turkey

chicks; as adults, turkeys can better

avoid predators in areas with mature

trees and little underbrush. Some birds

prefer no cover. Nesting terns require

sandy stretches of beach nearly devoid of

vegetation and use their bodies to shelter

their eggs and chicks.

• Space. Birds simply need the room to

find food, water, and cover. The amount

of space needed depends largely on the

availability of these elements. For

example, hawks and other raptors

require more acreage for hunting when

the abundance of prey decreases. The

need for space also mirrors the social

habits of the species. In winter, Darkeyed Juncos flock together, but on their

breeding grounds, these birds disperse

and defend territories.

Most species of birds space themselves

out for breeding, with males or breeding

pairs defending their territory. In

contrast, one-eighth of all bird species

nest in colonies, including swallows,

herons, gulls, and cormorants, and a

large number of young may be produced

in a small area. However, although a

nesting colony occupies less space than if

nests were widely dispersed, the birds

often require large areas nearby in which

to find food.

Multiple Habitats for Migratory Birds

Birds that migrate spend part of their

time in one habitat, and move to another

to breed. In addition to wintering and

breeding habitat, these birds require

stopover areas along their migration

routes. These habitats may be strikingly

different, depending on the seasonal

needs of the birds. The White-rumped

Sandpiper, for example, spends the

winter on beaches in Argentina,

hopscotches from wetland to wetland

across the Americas, and nests on the

mossy or grassy tundra of the high

Arctic. Because migratory species use

multiple areas, these species and their

habitats deserve our particular attention.

Conserving Quantity and Quality

Unfortunately, human activities and

development often result in the loss of

bird habitat. An area covered with

buildings or pavement simply cannot

provide the food, water, cover, and space

that birds need. To preserve healthy bird

populations, we must strike a balance

between our own habitat needs and those

of other species. With some birds, people

can establish conditions that allow for

cohabitation, such as green spaces in

their neighborhoods and cities. In other

cases, the long-term survival of a species

requires that people set aside areas from

development and disturbance.

People concerned about birds must also

protect habitat quality. Good bird habitat

must not only provide food, water, cover

and space, but must be free from

significant hazards. Birds face numerous

threats from human activity, including

poisoning by pesticides and pollutants,

entanglement in fishing nets and lines,

collisions with structures and vehicles,

and attacks by introduced predators such

as cats. People must work to reduce or

eliminate these hazards in order to allow

habitat to serve its function of providing

for a species’ survival.

Birds Need

Food

 Water

Cover

& Space