What is a Nest?
A nest is a structure made by birds to hold eggs. Nests are not bird
houses. The most common nests are cupped nests, but birds may make a
variety of other types of nests such as: ground or cavity nests, platform
nests and modified cupped nests.
Why build Nests?
Nests are important as they help keep eggs and hatchlings warm and provide protection from predators and the elements. They are a safe, warm place where the female bird can lay eggs and she or her mate can incubate them.
Ground and Cavity Nests
Ground nests were likely the first nests made by birds. They are usually
"scrapes" in a depression in the ground. The bird shapes the scrape with
her abdomen by rotating in the same place many times.
Ducks and geese make ground nests and then line them with down from the breast of the female, adding insulation. Other birds use existing natural cavities to build their nests. Insulated cavities shelter the eggs from cooling winds and allow the parent's body heat to warm the eggs efficiently. Woodpeckers excavate holes in trees, kingfishers excavate holes in sandy cliffs.
Most seabirds nest in colonies where the eggs are laid on the ground.
Although colonies may be easily located by predators, the great number of
birds present in the colony may actually deter predation as the birds
cooperate in surveillance and defense. Many nests may be predated but
the probability that any one nest is attacked is low, especially nearer to
the centre of the colony.
The first elevated nests were likely loose assemblages of plant materials.
Platforms eliminate risk from most ground predators. The platforms built
and used by herons, cormorants, eagles and osprey are very simple in
structure. Essentially they are flat areas with a slight depression to hold
the eggs. Often these birds use the same nest year after year.
Cupped nests are architectural marvels. They are the most solid, the warmest and the most complex
of the nests. Birds use various materials to build them.
They arrange and compact objects for the floor and the walls and
then use softer materials to shape the inner cup. When building a
cupped nest, the bird stands on the rim of the nest and puts materials
in place, tucking
in loose ends. The bird gradually produces the usual round shape. Most
songbirds build cupped nests.
Cupped nests may be suspended from branches and held by their rims and walls. Vireos build nests that are pensile. These nests are suspended from their walls and have very stiffly woven rims.
Orioles build nests that are pendulous. These nests are
suspended by their rims and have very flexibly woven sides. The deeply
cupped part of the nest swings freely.
Nest EcologyNests are often camouflaged in their environment. Ground-laying birds and their eggs are usually cryptically-coloured. Shorebirds and their eggs, for example, blend well into their rocky or sandy surroundings. Cryptic coloration helps to hide the eggs from would-be predators. Otherwise, ground-nesting birds may lay their eggs on islands or cliffs, areas that are relatively free of predators. When nests are built with materials from the immediate surroundings, the result is an inconspicuous or camouflaged nest.
Many small birds use spider webs to help glue nest material together. Some swallows use
mud to construct their nests; other birds use wet woodpulp and leafmold as well. Cave
swiftlets from Asia form their nests mostly from coagulated saliva, a delicacy in some
parts of Asia.
next... Laying an egg