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Birds' breeding cycle
Breeding behaviours vary within and between bird species and locations. The onset of spring, seasonal rains and the ensuing growth in plant, reptile and insect life, see many African bird species preparing to breed, including robins, herons and francolins. However various egrets, geese and sandgrouse generally wait for midsummer, seed eaters like melba finches don't start until autumn and a number of storks, spoonbills and vultures prefer to breed in winter. The reproductive cycle, beginning with hormonal changes in both sexes, sees one of a pair (usually the male) adopt attractive breeding plumage, establish a home territory and find a partner with whom to build a nest, mate and raise offspring.

Establishing a home territory
Having located a territory that will provide sufficient food for raising a family, a male proclaims his intended residency from prominent perches within it. His calling, usually most persistent around dawn and dusk, may go on all day. Challenges by other males in the area result in a sort of song ping-pong, through which boundaries are agreed. Thereafter intruders are aggressively driven out: ostriches, for example, have been known to chase a rival furiously for over a kilometre.

Finding a partner
Singing from the treetops also attracts the other sex. Like rivals, prospective partners are given a hostile reception, but soon the pair begin courting. Courtship usually starts with posturing. Birds variously erect crests, inflate necks, puff out throat pouches and chests, flap their wings about, cock and fan their tails and strut about, in order to impress a potential partner. Such displays are more common and more elaborate among those with colourful ensembles to show off.
Drab-coloured birds, on the other hand, are usually more melodious and given to serenading. Aquatic birds often enact courtship rituals in or on the water, while many land birds actively display by exhibiting on the ground - some, like Jackson's dancing whydah, doing so en masse. Others perform at the nest and quite a few species take to the air. Paired eagles soaring, gently circling, swirling, looping and free-falling with interlocked feet are particularly spectacular. So too are the hopping, leaping, wing-flapping and circle-running antics of cranes.
These courtship displays strengthen pair bonds, which in some cases may last a lifetime. They also stimulate the nest-building instinct in all but kestrels, cuckoos, whydahs and other parasites, which simply lay their eggs in the nests of another species.

Nest-building
Nest-building is an inherited trait, each species assembling a particular type of structure. Many build a new nest before each breeding season, but others reuse a site, modifying it each year. It is often the female who initiates the process, but the nest may be built by either sex, or both together. Certain babblers, shrikes and social weavers are among those who erect communal structures. Nests may be located on the ground, in grasses, reeds or thickets, in natural or pecked-out tree holes, in branch forks, in termite mounds, in riverbanks, in the burrows of various mammals, on cliff faces or rocky edges, in caves or suspended under overhanging rocks. Some species even use buildings, bridge arches, power lines or telephone poles for a home address. Birds dependent on water usually site their nests near, over or floating on it.
Materials commonly used in nest building include grass, reeds, twigs, rootlets, weeds, dry flowers, animal hairs, heather, stones and dead insects. These are sometimes bound together using saliva, moss, lichen, creeper tendrils, spider webs and excrement.
Building methods are as varied as bird species. In its simplest form, a nest may be little more than a dish hollowed in the ground or in grass, the bird rotating and using its chest to shape and compress the material.
Other rudimentary nests are made by compacting lichen or loosely piling up earth or vegetation. Often nests are simple loose-woven or tight-knit cups, but some birds, mostly songbirds, build very complex edifices. Weavers have the ability to knit and knot three hundred or so grass strands into a hollow globe-like structure suspended from a long branch, but many of the birds of prey employ little such skill in preparing platforms for their eggs. For small birds nest building usually takes about a week, but larger species may be at it for a month or more.
As the nest nears completion, the females of many species shed their chest feathers to form a brood patch. This area of bare skin, when in contact with eggs, allows body heat to incubate them. The discarded feathers and other soft materials are often used to line the nest.

Mating
Most songbirds and ducks mate for the first time when they are scarcely a year old, but eagles may only feel the urge three or four years later. When ready, the male mounts the female and simple contact of their reproductive openings results in the transfer of sperm to her oviduct and the fertilisation of her eggs internally. The pair will possibly mate several times before the first egg is laid. Some birds, plovers and sandpipers for example, produce a set number of eggs then stop even if some or all of them are lost. Others, however, will lay replacements and several species will have two or more broods in a season. The actual number of eggs laid may be an indication of the bird's life expectancy. Long-living birds that invest heavily in the parental care of their young usually lay a small number of eggs, whereas short-lived species produce large clutches and give their offspring minimal attention.
Some birds enjoy a bit of variety. For example, male Masked weavers and ostriches may seek three or four wives, the latter even inducing them to lay their eggs in the same nest. In contrast, Mrs Jacana happily looks after a small harem of egg-minding mates. As with humans, however, many birds find one spouse more than enough to cope with.