The nest is a key element both for survival and reproduction of bird species. Nests offer the essential care to eggs and offspring against physical stress, such as cold, heat, rain and predators. Bird nests are very diverse: from shallow cup into the ground to elaborate structures (artistic nests), built by the breeding pair or by a group.
The construction
Nesting is a real constructive work carried out in two contemporary phases: to collect the raw material and to arrange it. Harvest time depends on its distance, type of nest and climatic conditions. For some species, a nest is simply a shallow depression made in sand; for others, it is the knot-hole left by a broken branch, a burrow dug into the ground, a chamber drilled into a tree, an enormous rotting pile of vegetation and earth, a shelf made of dried saliva or a mud dome with an entrance tunnel.
The nest is built following specific procedures, according to its type. The builders of cup nests rotate and push the material from inside, while the builders of flat nest wheel and foot the material to fit it to the desired point. The shape is variable: the most common, globose or semi globe cup…..
Not all bird species build nests. Some birds, such as daytime and noctural birds of prey, lay the eggs in free nests (or usurped ones) built by other species, or in a natural site modeled with available materials. Brood parasites, such as cuckoos, lay their eggs in the active nests of other species, letting unwitting "foster parents" do all the work of rearing the young.
In most species, the female does most or all of the nest construction, though the male often helps. In some polygynous species, however, the male does most or all of the nest building. The nest may also form a part of the courtship display such as in weaver birds.
https://en.wikipedia.org/wiki/Brood_parasite
The materials
The construction materials are varied: natural or artificial, rigid or flexible soft, fresh, dried, earthy, fine or coarse.
Each species makes different choices depending on the constructive design and the area in which it is located, but with a great adaptability. The materials are usually arranged in layers, by placing the coarsest at the base and the finest and fluffy inside.
More elaborate nests also have a camouflage, made of lichen and moss.
The volume
The nest space is usually proportional to the size of the bird, but this may vary with the location of the nest.
Utilization
Usually a breeding couple uses the nest only once, but some species also use it for subsequent breeding. Generally, in temperate areas, nest-building coincides with the arrival of spring. That's when birds' internal "clocks" tell them it's time to mate and raise a brood. The eggs are laid just as the nest is completed, but some big-sized birds lay eggs several weeks later. For example, Western capercaillie leaves the nest, which is located on the ground, immediately after the hatching.
Nest identification
We need some key features to recognise a nest are: size, location, and structure. We must accurately identify the breeder or the egg to be sure of nest identification.
The nests and the nestlings must never be taken.
