Arrival at the nesting grounds is usually the signal for the beginning of the courtship display though, in some species, this may have started already in the birds’ winter quarters or during the return journey. The males’ behaviour is marked by agitation and excitement as they try to attract a partner. Each species has its characteristic manner of courtship: in some it is fairly inconspicuous while in others it is quite noticeable, often including intricate antics and loud cries.
The courtship display may take place on the ground, among the branches of trees, as well as in the air and on water. In some species, several males participate in the display simultaneously and even engage in duels. Among woodland birds, the black grouse provides a good example, the males of the species converging in a single open space for a mass display. The capercaillie, on the other hand, performs its antics at a higher level, usually on tree branches, and the ceremony consists of several stages.
The courtship display of cooing pigeons is also quite distinctive; they bow and strut about, or hop along and drag their wings along the ground. The male pheasant stands on the ground, stretches its neck upward and rapidly whirs its wings, at the same time emitting trumpet-like sounds that can be heard from a great distance. When courting the males of most songbirds sing, while other species produce unusual sounds. Woodpeckers, for instance, select that part of a tree which has good resonance and drum on it with their strong bills.
The courtship display of a number of species of birds includes spectacular flights. This is especially the case with the Raptors, which sometimes perform fantastic acrobatic feats. These aerial displays begin when the bird circles to gain height, then plummets downwards only to soar up high again, making all kinds of turns and somersaults and providing a magnificent display of its flying skill and artistry.
Prior to nesting, birds stake out a specific area called the nesting ground or territory. The boundaries of this area are
jealously guarded and defended by the male of the species. Once the territories have become established they are usually respected by the males of other species. The size of the nesting ground varies according to the amount of food available in the area and, in the case of birds which nest in tree cavities and the like, the abundance of nesting sites. Small songbirds have a fairly small nesting area, embracing a radius of some 40 to 70 metres from the nest.
Larger songbirds, like the crow and jay, have much bigger territories, while large raptors may require an area covering as much as several square kilometres. In this context, however, it should be understood that one nesting ground may be inhabited by several pairs of different species, birds that feed on different food and therefore are not rivals. Some species are colonial nesters, groups of birds foraging for food in outlying areas so that the nesting territory is limited only to the actual nest and its immediate vicinity.
When male songbird stakes out his territory he announces it to all and sundry by his characteristic song; woodpeckers drum on a tree trunk with their beak; pheasants have a special call note; many birds of prey emit a sharp cry and male cuckoos sound their ‘cuckoo’ note. In each case the message is clear:
this area is mine.
Before nesting, birds usually build a new nest in which the hen lays the eggs. Some species, especially songbirds, build complex nests that are almost works of art. It is often possible to determine the species of a bird by the shape of its nest, for the method of construction is a trait which is inherited, and, as a rule, a particular species will always use the same building materials. Buntings, for example, build their nests with stems of grass and horsehair. Some birds, such as woodpeckers, hollow out cavities in tree trunks, while others look for a ready-made cavity. Included in this group are tits, flycatchers, nuthatches and even certain owls and birds of prey, like the kestrel.
Some owls, on the other hand, seek out the abandoned nests of raptors, such as crows and herons. Other birds, like the woodcock, nest on the ground in a small depression lined lightly with leaves and some, like the nightjar, lay their eggs directly on the ground without any lining at all.
Each species produces eggs which have characteristic coloration and shape although some, like the cuckoo, lay eggs which show a marked variation. In the case of many songbirds, such as the flycatcher, chiffchaff, tit and wren, the eggs are incubated by the hen alone. In the case of pigeons, woodpeckers, certain raptors and some songsters they are incubated by both partners. Sometimes it is only the male that incubates the eggs and attends to the young; the dotterel is one such example amongst European birds.
Birds whose young have to be fed and cared for by the parents for some period after hatching are called nidicolous species. This category includes songbirds, woodpeckers, pigeons, owls and raptors. Those whose young are capable of independent activity from birth are called nidifugous species. Fowl-like species such
as the pheasant, capercaillie and black grouse are representatives of this group.
The young of songbirds and woodpeckers generally have no feathers when they hatch, whereas those of owls and raptors are covered with a thick layer of down. As a rule, the young of the nidicolous species are fed by both parents, but in the case of some raptors, such as the sparrowhawk, goshawk and falcon, the male hunts for the food and it is portioned and fed to the young by the female.
In such families, if a hen with young nestlings dies, the cock is unable to rear the family because he does not know how. Only the larger nestlings survive, namely those capable of tearing the prey that the male brings to the nest. The hobby is of particular interest in this respect in that the male follows this procedure with prey such as birds if he catches small insects will often feed the young himself Vultures feed their nestlings partially digested food, regurgitated from the crop into the bill.
The young of smaller types of songbirds remain in the nest for a period of twelve days before fledging, while those of larger songsters, such as the jackdaw, remain for about a month, As a rule, the parent birds continue to feed the young for a further two to three weeks after they have left the nest. The’ young of many species, thrush-types being a typical example, leave the nest before they are capable of flight and scatter in the neighbourhood, concealing themselves in the vegetation where the parents are compelled to seek them out to feed them.
This strange behaviour on the part of both young and parent birds has evolved as a protective measure to prevent vermin from destroying all the occupants of a nest. It is clearly more difficult to catch all of the scattered nestlings. The young of other, larger birds remain in the nest for about one month; those of large raptors such as vultures stay for up to three or four months.
The young of nidifugous species are capable of feeding themselves from the very first day of hatching. However, they venture forth only under the guidance of the parent birds and conceal themselves beneath the shelter of their wings during the night or in inclement weather, where they find not only a warm haven but also partial protection from vermin. The parents, usually just the hen, also lead their young to places where there is an abundant supply of food which the chicks can gather on their own.
Small songbirds, who often have large families to feed during the nesting period, seek food only in the immediate vicinity of the nest. Species that feed young less frequently, and obtain larger quantities at a time, often range a distance of several kilometres. This is true of raptors which fly far from the nest in search of large prey that will satisfy the entire family for some time. The golden eagle, which weighs an average of 4.5 kilograms, often returns with a piece weighing up to seven kilograms -—- a truly remarkable feat. Naturally such a catch is exceptional and may represent a two-day supply of food for the whole family. As a rule, the prey is much smaller.