Do all birds build a nest?

No. Most songbirds build an elaborate cup, platform, or cavity nest, but some species — most notably the common kestrel and other falcons — build no nest structure at all, instead laying eggs directly into an existing cavity, old crow's nest, or ledge.

Why do nest sites vary so much between species?

Nest site and structure are shaped by what predators a species needs to avoid and what materials and locations are locally available — a cavity-nester like a tit gets strong protection from a tree hole but is limited by the supply of suitable holes, while an open-cup nester like a swallow can build almost anywhere but relies on height, concealment, or human structures for safety instead.

Bird Atlas

Nesting

short

Nesting is the full process of building or selecting a nest site, laying and incubating eggs, and raising chicks to independence — behavior that varies enormously between bird families.

What nesting involves

Nesting covers the whole sequence from choosing a nest site through building (where applicable), laying the egg clutch, incubating the eggs, and raising the chicks until they leave the nest. The details vary enormously between families. The barn swallow builds an open mud cup plastered against a vertical surface, almost always now on a human structure such as a barn rafter or eave. The great tit instead nests inside an enclosed cavity — a natural tree hole or an artificial nest box — lined with moss, hair, and feathers. The common kestrel builds nothing at all, laying its eggs directly into a disused crow's nest, cliff ledge, or nest box.

Site choice and timing

Nest site choice usually balances protection from predators against the availability of suitable locations. Cavity-nesting species gain strong protection from a tree hole's enclosed walls but are limited by the local supply of old or decaying trees with existing holes — a constraint modern nest boxes are specifically designed to relieve. Open-nesting species like swallows trade that physical protection for much greater flexibility in where they can build, often compensating with height, an awkward approach angle for predators, or simply the general safety of nesting close to active human buildings that deter many nest predators.

Timing is tied closely to food availability for chicks: most songbirds time egg-laying so that hatching coincides with the seasonal peak in insect abundance, since a growing brood needs a large and reliable food supply for the few weeks between hatching and fledging. Species that raise multiple broods in a season, common among resident garden birds, effectively repeat the entire nesting cycle two or three times between spring and late summer.