Why Build Nest? Like most reptiles, the ancestors of modern birds buried their eggs in the soil or in rotting vegetation. During their evolution birds began using their body heat to incubate their eggs and a warm, protective nest was needed. During breeding season, longer days or rising temperatures stimulate hormones that trigger the building urge. One or both of the mating birds may build the nest, but the nest design remains the same in each species.

Tunnel Nest: The manx shear water lays its eggs in an old rabbit burrow or a cave like crevice safe from predators. The kingfisher tunnels into steep riverbanks, first pecking out a small hole. It then digs deeper, shoveling out sandy soil with its feet to make a chamber to house its white eggs.

Tree Holes: Woodland birds often use hollow trees for their nests. Dead or diseased trees rotted from the inside out provide deep, secure holes used by birds such as pigeons, parrots, owls, and starlings. The woodpecker enlarges its hole, but the wood duck and mandarin duck keep the holes much as they find them. Tree creepers and hornbills reduce the hollow openings by plastering the edges with mud to keep predators out.

Ground Nests: Birds nest in a variety of ways depending on the presence of predators, suitable nest sites, and nesting material. Common terns lay their eggs among beach pebbles, while ring necked pheasants nest down in grassy hollows. Some waders build floating platforms from twigs and leaves, held in place by rooted plants. The nests soon become waterlogged and rot, which allows the warmth of the decomposing vegetation to incubate the eggs.
Many smaller birds such as the lark make cup shaped nests in the earth to protect their tiny young. Hollowing the ground with their breasts, they weave layers of grass and wood stems into a cup shape and line it with moss and wool or hair. The nest and eggs are camouflaged, but predators such as weasels, foxes, and hawks can still find them.

Nest Above Ground: Tree nests range from huge, crudely built eagle aeries to skillfully woven, mud lined thrush nests. They are built in layers in a fork of a branch with twigs, wood stems, or tough grass depending on the size of the nest. Each piece is chosen for length and pliability before use. Large birds nest in treetops for easy flying access, while smaller birds often camouflage their nests with moss or lichen in secure, thick shrubs. The nests may be mud lined to make a dry, wind proof cup for the eggs, which are cushioned by soft materials and strands of spiders’ webs.

Key Facts:

Master Builders: Some birds improve on the basic cup shaped nest. Magpies crown their treetop nests with a roof of thorns to deter egg thieves. Tailor birds also build cone shaped nests by sewing together large leaves. The male pecks a series of holes down the sides of the leaves, stitching the leaf edges together with plant fibers. The ovenbirds make their rounded, roofed clay nests sometimes weighing up to 100 times more than the bird. Swallows also build enclosed mud and saliva nests, gluing them into building eaves so that heavy rains cannot wash them away.

Weaverbirds build a communal, weatherproof roof before building individual nest chambers under its protection. The most able of all nest builders, weaverbirds use threads stripped from large leaves to weave their circular or conical basket nests. The birds may use more than a dozen different kinds of knot. The completed weaver nest look like fruit hanging from the tree.

Did You Know:

Birds nesting in tree holes or tunnels lay white eggs that can be seen in the dark because they do not need camouflage.
The Egyptian plover sits on its eggs through the night and covers them with sand during the heat of the day.
The white tern does not really build a nest. It sticks its eggs to a branch with a glob of mucus instead.
Unlike most birds, which build their nest of plant material, the swiftlet builds its four inch wide nest from saliva over a one month period.
Some eagles build such a huge aerie (nest) that small finches have room to nest in its branches. It provides a good base for their nests and protection from predators.

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