SEVEN

Finding Partners

The process of securing a mate may be imperative but it should also be selective; and it is usually the female who makes the selection. First she must assure herself that a prospective partner belongs to the same species as herself. That is necessary in order to avoid wasting time with a partner with whom she cannot have a fruitful union. The question should be easy for her to resolve for a male has already gone to some lengths to identify himself to his rivals and the signals he used for them are likely to serve her equally well. If there is any possibility of confusion, the males usually go out of their way to make the position clear. The blue-footed booby, which breeds on the western tropical coast of South America and on the Galapagos Islands, shares some of its nesting sites with the red-footed booby. The two species are very similar, except, as their names make obvious, in the colour of their feet. So when a blue-footed male wishes to attract a female, he makes sure she knows who he is by dancing, lifting up his ultramarine webbed feet with all the care and exaggerated movement of a man wearing snowshoes.

Once that possibility of confusion has been cleared out of the way, a female will next need to satisfy herself that her partner is capable of giving her all the help she needs to raise her chicks. A female European wren expects her mate to provide her with a nest and a male may build up to a dozen nests in different sites before he produces one that convinces a female that he will be an adequate partner. African masked weavers build in colonies and females look for a male with a well-sited nest in the colony’s tree, preferably dangling from the tip of a high branch so that it will be difficult for a marauding snake to reach it. She also requires that a nest should be firmly woven so that her eggs do not fall through its floor, and be strong enough to hold the chicks as they grow and become increasingly heavy. A male weaver seeking a mate must therefore become a speculative builder. Having woven a nest, he hangs beneath it, fluttering his golden wings and shrieking every time a likely female flies by. If she approves of his work, she will join him. A youngster in his first year may stand little chance against more experienced males who quickly produce much better nests than the somewhat sloppy, untidy version he usually makes at his first attempt. He may be rejected so many times that he becomes discouraged. If the green of the freshly gathered woven strips fades to brown, a female will not even bother to inspect it. Why should she waste her time considering the nest of a suitor who has been rejected for so long by so many? After some time without success, he laboriously unravels his construction to make a second attempt on the same precious site. Often, he has learned from the mistakes of his first, but often too he may not manage to attract a female at all during his first breeding season.

Penguins make minimal nests. The gentoo, which also lives in large colonies, uses little more than a scrape on an expanse of bare Antarctic shingle. Nonetheless, both male and female like to have it ringed by little pebbles and a male will pick one up in his beak and show it to a female as an indication of the sort of thing he might provide were she to join him. The end result is more handsome than might be guessed, with all the constituent pebbles being very similar in both size and shape and most neatly arranged. Adelie penguins do much the same. They make their nests in the far south on the continent of Antarctica itself and have similar nest-making rituals, though for them fragments of ice may serve just as well as pebbles.

Many females will require their mates to supply food for them when they are sitting and for the young when they hatch. A male tern starts his courtship by demonstrating his ability to do this by bringing the female a gift of small fish, held cross-wise in his beak. He continues to make such presentations long after he has been accepted as a partner and does so immediately before each copulation. So while his initial offering might have been a ceremonial proposal, subsequent ones become a valuable element in the female’s nutrition while she builds up the bodily reserves she needs to produce her eggs.

The female peregrine has similar expectations of her partner. If he is to live up to them, he has to be a highly competent flyer, so in the airspace above the nest site that he has claimed, he demonstrates his prowess by a dazzling display of aerobatics. He spirals upwards to a great height and then plunges down at speed. At the bottom of his dive he swoops up again, sometimes rolling rapidly from side to side, sometimes looping the loop with wings half-closed. The female may join him in this demonstration of aerial skill. The two will swoop on one another, sometimes interlocking talons to tumble downwards through the air, sometimes coming so close together that while in mid-flight they touch their breasts or beaks in an aerial kiss. Tropic birds also indulge in these graceful and breathtaking courtship flights, sailing back and forth in tandem, their long filamentous tails undulating behind them and moving in such perfect synchrony that often it is impossible to tell which of them is initiating the movements of their aerial dance.

Skills in nest-building, fishing or hunting are obvious qualifications for a mate but in many species, a female makes a rather more generalised assessment to assure herself that her partner is in good health and likely to pass on his strength and vigour to any offspring they may together produce. If he is one of those birds that sing during their courtship, the quality of his song will provide an indication of his suitability. Singing, after all, takes a lot of energy. It also exposes a bird to his enemies, something that could be fatal for individuals who are in less than prime condition. Furthermore, a male who can afford to spend a lot of his time singing is clearly either feeding in a notably effective way or the owner of a particularly rich territory. In either case, he is a desirable partner.

She can also deduce his desirability from his plumage, using much the same criteria as the male displays when establishing his rank among his rivals – the brilliance of the bullfinch’s scarlet breast, the size of the white patch on the forehead of the collared flycatcher, the assurance of a blackbird’s song and the glossiness of his sleek black plumage setting off the intense yellow of his bill.

So in spring, males are at their most colourful and smartest. The females, who are doing the choosing, have less need to be strikingly coloured and indeed it may be better that they are not, for most will have to undertake some if not all of the incubation and when sitting on the nest it will be safer for them to be inconspicuous.

In those species where the sexes are similar or identical, the birds may select their partners by dancing together. All species of cranes do so. They gather in groups of a dozen or more and begin to bow and leap to one another. They flap their wings, bounce into the air and make sudden frantic runs. Sometimes they will pick up a feather or a twig and throw it into the air as though it were a toy.

Grebes perform a long series of ritualised dances on the lakes and rivers where they live. A pair of great crested grebes start their courtship by swimming up to one another, meeting breast to breast and then, in silence, twisting their heads from side to side, flaunting the broad chestnut ruffs around their necks and the long black ear-like tufts on their heads. Other rituals follow as the days pass. The female will swim with her neck stretched forward and her beak close to the water surface, calling as though looking for the male. As she nears him, he makes a shallow dive and emerges in front of her, holding himself upright with his beak pointing downwards. If over the next few days their relationship matures, they begin to perform the weed dance. The partners swim away from each other and then both slowly submerge. After a few seconds, they reappear on the surface, both carrying a small bundle of weeds in their bills. Ceremoniously, they swim towards one another until they are face to face and almost touching. Then they lift up their bodies erect and, beating their feet, rock their heads from side to side with the weeds still dangling from their beaks. The western grebe, which lives in the western United States, has an even more spectacular climax to its ceremonies. Instead of posturing with weeds, a pair will rise up alongside each other with necks stiffly arched and on thrashing feet scoot wildly across the surface of the water like a pair of water-skiers towed by an invisible boat, until suddenly and simultaneously both dive below the surface.

Male and female puffins develop special and identical decorations for their courtship. During the spring, they grow a horny outer covering to their beaks, handsomely striped with yellow, red and blue. When breeding is over, this particular extravagance is shed, for it may well be an encumbrance when trying to catch fish underwater.

The brightness of the colours assumed at the beginning of the breeding season tells the females of many species that the particular individual they are considering is indeed of the opposite sex, as does his general bearing and, often, his elaborate and confident song. But some birds provide permanent indications of their sex. Male and female sulphur-crested cockatoos have identical plumage, but the male has a darker eye than a female. The male European greater spotted woodpecker has a crimson patch on the back of his neck which the female lacks. The Namaqua dove, whose call is one of the characteristic sounds of an African evening, differs sexually in that the male has a black face and the female does not.

Other males are even more explicit. The African superb sunbird is indeed superb for the male has a maroon belly and an iridescent head; but only the male deserves that name, for the female is dressed in dull yellow and olive. The Australian king parrot male is brilliant scarlet whereas the female is green. The sexes of another Australian parrot, the eclectus, are so different that for many years ornithologists thought they were two different species. Then someone noticed that one group of emerald-green parrots with scarlet underwings and flanks were all males, and another group from the same area, which were entirely crimson except for their violet blue bellies, were all females and put two and two together.

Male frigate birds declare their sexuality with a fleshy adornment that they display only at the breeding season. They are seabirds that wander across the oceans of the tropics and only come to land in order to breed. They choose remote islands – the Galapagos, Raine Island on the Barrier Reef, Aldabra in the Seychelles and Ascension in the middle of the Atlantic among them. The males claim a nest site first and take up residence. Having done so, they do not leave it, for suitable places are few and another male is likely to claim it if it is abandoned for any length of time. So the nest-holder sits tight and from that position does his best to summon a female by inflating a pouch beneath his throat. For several minutes he repeatedly fills his lungs with air and expels it into his throat pouch. Watching him do it has all the suspense of watching someone blow up a balloon at a birthday party. The billowing scarlet pouch gets larger and larger until it is drum-tight and close, surely, to bursting. As if this huge sign were not conspicuous enough, the male also calls to females flying past by stretching out his wings, vibrating them and making loud gobbling noises.

Many male birds sprout special plumes to adorn themselves for breeding. Male egrets grow long white filigree feathers down their backs that they can erect in display. Male ducks go through a complete change of costume. The alteration in their appearance can be so extreme that it is difficult to believe that the gaudy creatures, pirouetting, nodding their heads and erecting banners on their flanks, are the same birds as the dull brown ones that were swimming on the lake only a month or so previously. Mandarin and teal, mallards, harlequins and eider, all change into dandies with the most extravagant costumes. A month or two later in midsummer, when breeding is over, they will moult their brightly coloured nuptial dress and become once more modest and retiring.

As a result of these displays, males and females form pairs. Some birds find a different partner each year; others, such as swans and albatrosses, mate for life. Some pairs share tasks of nest-building and chick-rearing more or less equally; others will split just as soon as incubation starts. There are polygamous males and also females who take several male partners. But overall, some 90 per cent of bird species are monogamous.

Some of the males in that remaining 10 per cent, are not only polygamous, but take no part whatever in family life. Their relationship with their females is limited to the few seconds that it takes to copulate with them. For that to happen, the species has to live in a place where food is so abundant and easily gathered that a female can manage to rear her family entirely by herself. But if a female no longer requires her mate to help her build a nest, or defend a territory or provide food, what quality would make her prefer one male to another? Her only concern need be that he is healthy and vigorous and likely to pass on that strength and general fitness to her offspring. Like monogamous birds, she can judge that, to some extent, from the quality of his plumage, and the way he displays it. Many females certainly use such criteria as the basis of their selection.

This has been demonstrated by a series of ingenious experiments involving the whydah, a relative of sparrows with black plumage and scarlet shoulder patches that lives in swamps and marshes in East Africa. The males are polygamous, and hold territories in the reed beds in which their several females build their nests. During the breeding season, they develop broad, black tail feathers 60 centimetres long and display them in fluttering flights above their own patch of reeds. The experimenters cut off half the length of the tail feathers of some males and increased the length of some others by the same amount. They then counted the number of females each group acquired. The males with shortened tails attracted half as many females as those birds with a normal length; and those with super-tails doubled the number of their females.

Breeding only from the few individuals who exhibit a physical characteristic at its most extreme and excluding the great majority that do not reach that standard is, of course, a technique that has long been used by human breeders of livestock. Pigeon fanciers used it to produce an extraordinary variety of descendants of the wild and unremarkable rock pigeon. They bred pure white birds and all black ones, birds with feathers on their feet, with grossly inflated chests, with exaggerated tails like huge fans, with feathers pointing forwards along the back of the neck to form a hood around the head and many more bizarre forms. Those results were obtained within a few decades. Some wild female birds have been selecting their mates on the basis of their appearance for tens if not hundreds of thousands of years. The results they produced became so extreme that different breeds became unable physically to mate with others. So, genetically isolated, they eventually became new species.

Nowhere has this process produced more spectacular results than in New Guinea, that immense 2,000-kilometre-long island that lies north of Australia. Its forests and swamps are particularly favourable environments for birds. Like most in the tropics, they are swarming with insects, rich in fruit-bearing plants, full of potential food of one kind or another. The island also has another advantage for any bird that lives there. It is, in evolutionary terms, a very young land having been formed some ten million years ago by volcanoes erupting from the floor of the Pacific Ocean. As a result, the only mammals that managed to reach it before humanity were a few marsupials from nearby Australia and some bats. There are no monkeys stripping the trees of fruit or leaves, no squirrels collecting their seeds. So birds there have very few competitors for the forest’s food and a female can without too much difficulty gather enough for herself and her chicks unaided. Not only that, but the island has no large mammalian predators either – no jungle cats, no weasels, raccoons or foxes. So attracting attention by displays or being encumbered by extravagant plumes does not necessarily put a bird in danger. Male birds of paradise have exploited these opportunities to an astonishing degree.

The bird-of-paradise family is thought to be distantly related to the crows. The forty odd species that now live in New Guinea vary in size from a magpie to a robin. The females and young males all look remarkably similar, as one might expect members of the same family to do. Most have brownish backs and pale breasts that are barred, speckled or in a few instances, plain. The mature males, however, have such varied and extravagant decorations that it is difficult to believe that they could be related to one another. Some have plumes sprouting from their flanks, others from their shoulders, their chin or their forehead. One wears a tiara of six quills each tipped with a black disc, another is bald with the skin of its scalp a piercing blue. And they flaunt these astonishing adornments in as great a variety of ways as it is possible to imagine.

The black sicklebill, the largest of them all, is entirely black but has feather fans, rimmed with iridescent blue on either side of his breast. The species lives in such remote parts of the mountains that until very recently no scientist had seen it in display, so that one could only guess how these fans were exhibited. It turned out that the bird, perching on his display branch at dawn in the middle of his territory, suddenly erects them so that they frame the whole of his head. At the same time he spreads his long black tail and changes from a shape that is recognisably bird-like into a sinister looming rectangle. Then he sways and tilts sideways until he is almost horizontal. The smallest species, the king bird of paradise, is scarlet with creamy white underparts and two quills projecting beyond his tail, each tipped with an iridescent green disc. He displays by first erecting tufts on his chest and then suddenly toppling down so that he hangs upside down from his branch with his wings open and vibrating. He remains there for a few seconds, then he closes them and with muscular movements of his legs swings his body like a pendulum so that his two tail quills thrash from side to side. The King of Saxony bird of paradise has two feathers that have such an extraordinary structure that when they were first examined by ornithologists, before the bird itself was found, they were thought to be some kind of forgery. They sprout from his forehead and are twice the length of his body. The quills, instead of carrying normal feather barbs, have on one side only a line of small sky-blue platelets which are so hard and shiny they resemble enamel. His favoured display perch is always a thin dangling vine. When he performs, he throws his two extraordinary plumes forward and then, flexing his legs, he kicks repeatedly downwards, like a child trying to make a swing rise higher and higher until the whole vine is bouncing. As well as wearing a fantastic costume he is also, in effect, a trampoline artist.

Nor do all birds of paradise display in trees. Because of the absence of ground predators, it is possible to perform in safety on the ground. Some do. They clear a dancing stage on the forest floor by snipping off the leaves from the surrounding saplings and removing all twigs and any other litter from the ground to expose the surface of the earth. If you find one of these arenas in the forest, it is easy enough to discover if its creator is still around and active. All you have to do is to throw one or two leaves on to it and hide. If he is about, you will first hear a few agitated calls and then the bird himself will fly down, pick up the leaf in his beak and, with a flick of his head, throw it away to one side.

The performances enacted on these stages are just as varied as those by other species in the trees. The bird with the blue bald head, Wilson’s bird of paradise, has a scarlet back, a sulphur-yellow patch on the back of his neck and an iridescent green breast. When he displays, he clings to the vertical stem of a sapling and distends his breast feathers into a shining green shield fanned out at right angles to his body. The birds of paradise with the head pennants, the five species of parotia, look at first sight to be some of the more sober members of the family: except for a white disc on the forehead, the males are dressed entirely in black. Theirs, perhaps, is the most theatrical performance of all. Before a male parotia starts, he inspects his dancing stage with great care, removing any fragment of leaf or twig that might have fallen on it since he was last there. Then he makes a series of scuttling runs across the stage, letting out shrill calls. This announces that he is about to give a performance and usually an audience of several drab females will arrive within a few minutes and take up their seats on a horizontal branch to one side. As they settle in, he makes another tour of the stage. It is immaculate, but even so, just to underline the point, he mimes, pretending to pick up non-existent leaves and then casting them aside.

And now he begins his dance. He lifts himself high and holds out his long body feathers so that, with his wings, they form a circular skirt like a crinoline. He erects his breast feathers so that they catch the light and you can see that although they had seemed plain black, they are in fact iridescent and form a glinting shield, part greenish-blue part gold. Facing his audience, he waltzes from side to side. Abruptly, he stops and for a moment is rigid. Then, standing on the spot with feet astride, he begins to twirl his head so that the pennants of his tiara are lost in a blur. Suddenly he leaps into the air, lands on to the back of one of the females in the audience and mates with her.

Female birds of paradise tour all these varied performances and, one must assume, compare each male and select the one who impresses them most. Human observers who wish to interpret the females’ judgement in a strictly practical way may say that the athleticism of a male’s dance and the splendour of his plumage are accurate indicators of his vigour and therefore genetic superiority. Others may also conclude that the female bird of paradise must have an aesthetic sense which leads her to prefer a brighter colour to a dull one, a more extravagant decoration to a more modest one.

Another group of New Guinea birds provides evidence on this point. Bowerbirds are found over much the same geographical range as the birds of paradise and were once thought to be closely related to them, though genetic studies have now shown that this is not the case. One species is golden yellow, another part-yellow part-black, and several others in the family are plain brown and only have yellow feathers in their crests. They too indulge in extravagant courtship displays but instead of using their feathers, they do so with collections of brightly coloured treasures – berries, shells, flower petals, even bits of glass and fragments of plastic. These they exhibit in special constructions of twigs, their bowers.

The toothed-billed bowerbird in the rainforest of northern Australia constructs the simplest display. He merely clears an area of the forest floor and then saws off the large leaves of a particular tree with his toothed bill and carefully lays them out on his stage with their pale sides uppermost. Others, including the satin bowerbird, build a metre-long avenue flanked on either side by walls of twigs. At each end of this, the male places his collection of shells, bones and berries. This is strange enough, but one other group, the gardener bowerbirds, all but one of which live in the New Guinea forests, build even more elaborate treasuries. One of these gardeners, MacGregor’s bowerbird, selects a slim vertical sapling and builds a tower of twigs around it. This may be 3 metres high. Round its base he clears a circular runway, banked with a low outer wall faced with moss. He then summons females with long liquid calls. When one arrives, he picks up a flower in his beak and dances around the runway, peeking around the central column first from one side and then the other. The striped gardener produces a more flattened version of this construction with the top of the tower extended outwards and down to the ground so that it forms a cave with an entrance on one side. On the floor of this cavern he scatters flower petals.

The most complex bower of all, and surely the most remarkable construction made by any bird, is the hut built by the Vogelkop bowerbird. The biggest I have seen looked like a man-made hut, for it was big enough – just – to crawl into. Two saplings in the centre supported its conical roof, thatched with the dried stems of orchids. The ground immediately in front of it was planted with a lawn of moss. On this lay the owner’s treasures, neatly arranged in piles according to their character – black beetle wing-covers, scarlet berries, shiny black fruits as big as plums, the huge squat acorns of the local oak, fragments of orange fungi; and, most luminous of all in the dim forest light, a great heap of orange-coloured dead leaves. There were at least half a dozen other bowers within a kilometre or so. But they were not all the same. Other individuals had chosen other coloured objects for their collections. One had clearly become enchanted by the pink flowers of a creeper that must have just come into bloom in the neighbourhood, for a huge pile of its blossom lay to one side within the hut.

The notion that these bowers and their contents play the same part in the lives of bowerbirds as plumes do for birds of paradise is supported by the fact that among these gardener birds, at least, there is a direct and inverse correlation between the colourfulness of their plumage and the complexity of their bowers. MacGregor’s bowerbird, the maypole builder, has a large orange crest which extends almost halfway down his back; the creator of caves, the streaked bowerbird has one which is only two-thirds as long, fringed and streaked with brown and invisible unless erected; and the Vogelkop bowerbird, the most extravagant gardener of all, is a plain brown bird with no crest whatsoever.

It might seem that the bowerbird’s way of displaying is much more economic than growing feather adornments as the birds of paradise do. It does not require a male bird to squander his physical reserves on feather finery that has to be renewed annually, nor does it incommode him in flight. On the other hand, watching these birds at their bowers leaves you in no doubt that owning and maintaining such collections is very labour intensive indeed. The Vogelkop bowerbird worked at his bower almost continuously throughout the day, bringing in new treasures and rearranging those that were already there so that they were displayed to their best effect. He was not able to abandon it for any length of time for if he did, one of the males from a nearby bower would certainly fly in and steal choice pieces. Furthermore some species tend their bowers for as long as nine months in the year. So maybe the size and splendour of a bower is indeed a fair measure of the vigour of its owner and therefore his desirability as a mate. But the fact that the bowers varied in their contents suggests that males had found that it was a viable strategy to proffer particular colour arrangements of their own, which must mean that females have aesthetic tastes that vary from one individual to another. Certainly, female bowerbirds tour the bowers, just as female birds of paradise tour the dancing grounds of their males, apparently assessing their relative merits and then mating with the architect of the bower that takes their fancy beside or even within his prize-winning construction.

One group of birds of paradise, the first to become known in the west and still the most famous, simplify the females’ task of selection by displaying in groups. The males have bunches of gauzy plumes that sprout from their flanks beneath their wings and extend well beyond their tails. Those of the greater and lesser birds of paradise are golden; the Raggiana bird of paradise has scarlet ones. As many as ten glorious males of one of these species will assemble in a tall tree that may have been used for this purpose for many generations. Their display involves flapping their wings, shrieking and fluffing out their gorgeous plumes and they keep doing so intermittently throughout the day. The arrival of a female, however, sends them into an ecstatic frenzy. They lower their heads and erect their plumes over their backs in a fountain of colour. But each bird stays on his own branch of the tree that he uses every day. It is for the female to fly down and join one of them.

Sustained observation of these group displays reveals that nearly all the visiting females mate with the same male. Have they, in fact, surveyed all contenders who look almost identical to our eyes and all, unerringly, chosen the same individual? Or could it be that in such groups, it is the perch that tips the decision between one resplendent male and another? If that is the case, then it could be that the males’ displays are directed not so much to the females as to one another. This might create a ranking system in which the most senior male claims the display perch where all the mating occurs.

Another tree-displaying bird of paradise seems very likely to be operating in this way. The standardwing bird of paradise lives only on the island of Halmahera and two smaller islands off its southwest coast. It is the most westerly of all birds of paradise. Its plumage is not perhaps the most ravishingly beautiful but it has to have a fair claim to be the oddest. It has a slender purple cravat on its breast that normally lies close to its flanks and extends right down to its tail. It also has two long white feathers that dangle from the middle of the leading edge of each wing. The males assemble in even greater numbers than the Raggiana bird of paradise. The species is so rare and little known that for a hundred years after its first discovery by science in the middle of the nineteenth century it was never sighted again. Only relatively recently was one of its display trees rediscovered. It stands in the midst of the forest and when I visited it, there were so many displaying males that some were displaced into the somewhat lower trees growing beside it. There were between thirty and forty of them. They displayed to one another by erecting their cravat horizontally so that it glinted, purple changing to green, and twirling the white standards on their wings. Those on the periphery of this great assembly called attention to themselves by display flights, shooting vertically into the air on rapidly beating wings, floating for a few seconds at the top of their jump with wings rigidly outstretched and then sinking down again to resume their quarrelsome displays with other males. Determining whether or not females were present was not easy for, as in so many of these birds, there is no way of being certain whether a bird without plumes is a female or an immature male. But even allowing that most were females, it seemed hardly credible that any one of them could survey the whole displaying multitude to make a proper judgement between them. Yet here again, all the copulations were taking place on just one branch and, seemingly, with just one male. If it is indeed the perch that determines the females’ choice, then the extravagance of the males’ plumage is due, not so much to the females’ delight in beauty but to the males’ assessment of what is most daunting.

Several other families, as well as the birds of paradise, display in this way, the males dancing either in one dazzling group or separately, each on his own stage but sufficiently close together for the females to move easily from one to another to make their comparisons. This phenomenon is known as a lek, a term derived from a word meaning flirtatious play, first applied by Scandinavian ornithologists to ruffs, sandpipers that dance in this way. The male ruffs grow extravagant plumes on their heads and necks which vary considerably in colour, some black, some white, some reddish dappled with black. A dozen or so will assemble on open land and parade there while the smaller soberly-dressed females move among them to select their mates.

The buff-breasted sandpiper breeds farther north in Canada. They are more discreetly dressed and dazzle the females by showing off their white underwings. When a female approaches the lek a male will flash open one of his wings. If this action catches the female’s eye, she will pause in front of him waiting for a repeat performance. He may open either wing, but if he becomes particularly excited he suddenly spreads both while several females cluster in front of him, often totally ignoring another male sitting nearby who – no matter how energetically he exposes his armpits – seems not to have what it takes.

Several bird families seem particularly prone to this kind of polygamy. In Europe and Asia there are pheasants and their near-relations, the grouse. The peacock belongs to this group and has perhaps the most spectacular adornment of any bird, but there are others that come close to it in extravagance and magnificence. Bulwer’s pheasant has an ultramarine wattle hanging on either side of his face. When he becomes excited, the upper half of his wattles above his eyes engorge with blood and rise up as two vertical spikes, while the pair beneath the eyes quadruple in length and extend right down his chest. The great argus pheasant is equipped with immensely elongated wing feathers which he fans out into a vertical screen. He then peers at the female through the centre of it with one glittering eye. The sage grouse spreads his tail so that the pointed feathers form a spiky sunburst behind him, lowers his folded wings, and inflates a huge pendulous air sac on his chest. As it increases in size this exposes two patches of naked olive-green skin and eventually conceals his head altogether.

In South America, richly costumed displays are exploited to a spectacular degree by the cotingas. Male umbrellabirds have pendulous lappets hanging from their throats, red or black according to the species, and black feathers on their heads that are equally long on all sides and hang down so that they look more like badly fitting wigs than umbrellas. They call with a deep flute-like note from the tops of trees, and females fly from one male to another. The capuchinbird, like lekking ruffs, displays in large groups, but in treetops. At first sight they seem rather drab with uniform russet-brown bodies, black wings and tail, and a naked head. But they become more dramatic when they display – rearing into a near-vertical position on the branch, everting a pair of small cream-coloured globes on either side of the tail and letting out a quite unexpected call. Another name for this species, calfbird, comes from its sound, but to compare it to a calf’s bellow does it an injustice: it certainly has a moaning quality, but with strange electronic overtones. They produce it by inflating a throat sac, which swells so much that the feathers which normally cover it lift away from the sides, exposing the throat sac’s walls, which are so transparent that you can see right through them.

The most brilliant of the family are the cock-of-the-rocks, of which there are two species – the males a startling red or orange, with a feather cockade on the head which extends almost to the tip of the beak. While awaiting the approach of a female, they perch 3 metres or so above the ground in the forest undergrowth, squabbling and squawking among themselves. But when she arrives they all flop down to the ground, each on his own small plot, and squat there and start to make little bouncing hops. The greyish female shows her choice by fluttering down behind one of the males and giving him a sharp peck on his rump. For a few seconds he stays motionless as though he can hardly believe his luck. Then he suddenly turns and jumps on her back for a swift copulation.

By and large, the more elaborate a bird’s costume the less complex its vocalisation. It seems that a bird has little need to invest in both. The plumage of the peacock and birds of paradise may be flamboyant, but their calls are harsh and simple. But there is one conspicuous exception to this generalisation. The male lyrebird has long, gauzy tail feathers flanked on either side by a curving feather with its vane richly patterned in brown and cream. The males each have their own display mounds in the southern Australian forest, on which they dance, and the females tour them to make their choice. When the male displays, he bends his tail forward over his back and fans it out in a most spectacular fashion. But at the same time, he sings one of the longest, most melodious and complex of all bird songs. This must mean that the females not only admire visual beauty but have, in addition, a predilection for vocal brilliance and coloratura. The males, in their need to increase the length and variety of their song and outdo their rivals, have become superlative mimics. They include in their cascades of trills, warbles and liquid notes, the songs of almost every bird in the surrounding forest. Even the most inexpert birdwatcher can identify and admire the accuracy of a lyrebird’s kookaburra impersonations, but a skilled ornithologist may be able to recognise the songs of over a dozen other birds embedded in the lyrebird’s incomparable recitals. Some individuals have territories close to those occupied by human beings and they incorporate the new sounds they hear coming from across their frontiers. So they include in their performances accurate imitations of such things as spot-welding machines, burglar alarms and camera motor drives. The female lyrebird, it seems, is an aesthetic glutton. Like an over-demanding opera-goer who is only satisfied if her tenor has a slim athletic figure as well as a dazzling voice, she tries to find a mate who is as beautiful to look at as he is to listen to.

Most avian polygamists are male, but in a very few instances it is the female who has multiple mates. The red-necked phalarope, a small wader, nests on the ground on the open Arctic tundra. Being so exposed, its eggs are frequently lost to predators. The females of many species, after such a disaster, will lay again. And so does the phalarope. But she has made the practice a routine one. Having mated with one male, she leaves him to take care of the incubation and moves away to find another male who will do the same thing. In one season, she may have as many as four mates and four families of chicks. It is advantageous for any sitting bird to be well camouflaged, so it is not surprising to find that the male phalarope is dully coloured. The female, in contrast, is the one who has the redder neck. She is also bigger and she is the one who will display when initially claiming a nest site.

The American lily-trotter or jacana also nests in dangerous circumstances. In the lakes and ponds where it lives, there are threats from crocodiles, snakes and birds such as purple gallinules that will readily eat eggs or chicks. A female will claim large tracts of this dangerous territory and attract as many as three males, each of whom builds a nest within her domain. She stays with each male for a few days of courtship before she lays a clutch of eggs in his nest but thereafter she may never visit him again. She does, however, maintain watch on the whole of her territory and zealously drives off intruders. Why this reversal of the normal role of the sexes has taken place among jacanas and phalaropes is still an unanswered question.

The complexities of courtship, monogamous or polygamous, are only the preliminaries leading to the crucial act of copulation. For an event of such importance, it is completed in a remarkably short space of time. Indeed, many people seeing it may understandably doubt whether it has happened at all. The male hastily and awkwardly clambers on to the back of the female, she bends her tail to one side, he to the other, the two genital openings are pressed together for a second or so, the male tumbles off and it is all over.

Male birds, with very few exceptions, do not have any organ such as a penis which can be inserted into the female to place the sperm deeply and securely inside her body. Why should this be? Perhaps it was lost, ancestrally, as part of the trend towards reducing weight. Maybe it also has something to do with the fact that maintaining your balance while standing on two legs on a narrow perch with another individual on your back is not an easy thing to do for any length of time. Even on the ground, a lengthy copulation could be dangerous since most birds have only too many terrestrial enemies and may need to take to flight at a moment’s notice. So it may be better for the pair not to be physically connected so intimately that separating within a second or so is difficult. Whether that is so or not, sperm is transferred from male to female almost instantaneously by a fully cooperative act. A bird has only a single rear vent, the cloaca, which leads to both the end of the gut and the sex ducts. Both the male and the female are able to turn it inside out and they do so during copulation. The male’s duct leading from his sperm sacs and the female’s oviduct meet end to end and sperm is transferred within seconds. Swifts, indeed, are able to complete it in flight as they glide.

For a few birds, this brevity is either unnecessary or impractical. Those that live mostly or entirely on the ground have much less difficulty in keeping their balance for they can crouch – and ostriches, storks and curassows do indeed have a long extension of the lower wall of the cloaca that acts like a penis. That of the ostrich is bright red and nearly 30 centimetres long. Ducks have a special problem. They mate on water and when the male mounts, the female may be almost submerged. Under those circumstances, sperm could well be washed away and lost unless it is deposited deep inside the female. So ducks, like ostriches, have an organ with which to inject sperm.

The transfer of sperm, however, does not necessarily guarantee that the male who produced it will be the father of the chicks hatched by the female who received it. It takes time for sperm to travel up the oviduct and unite with an egg. In some species, the journey may be completed in no more than half an hour. In others, sperm may remain alive in the oviduct for days, even weeks, and fertilise successive eggs as they are produced from the female’s ovaries. So many males take steps to ensure, as best they can, that none of their rivals have access to a female after they have mated with her. There is an old saying in England that, in spring, you never see a single magpie. If you see one there will always be another nearby – and even a third. A male magpie, after copulation, keeps very close to his mate, accompanying her whenever she stalks across the fields looking for food, trailing after her as she goes down a hedgerow searching for a nest to raid. Many other less conspicuous birds such as chaffinches behave in much the same way. If another male approaches the pair, the mating male will do his best to drive him away.

The male hedge sparrow – more properly called a dunnock or hedge accentor, for it is not a sparrow at all – varies its marital arrangements according to the quality of the environment around its nest. If there is plenty of food, then a female may be able to rear young with little help and a vigorous male may attract two or three females, each of whom builds her nest in his territory. If, on the other hand, the territory is poor in food, then a female may need more help in caring for her young than one male can provide. In such a case, she may be able to recruit the help of a secondary male. Her senior mate, who initially established the territory, remains her ostensible partner, singing conspicuously to defend its boundaries and mating with her frequently out in the open. The secondary male is much more retiring. The senior male tolerates having him around for he helps in rearing the chicks. But the female offers her own rewards. If she can escape the senior male’s attention, she and the junior male will mate hidden quietly in the bushes out of the senior male’s sight.

The senior male dunnock does his best to avoid being cuckolded by keeping a close eye on his female. But he has an additional strategy to reduce the possibility of her laying eggs to which he has not contributed. He starts his copulatory display by chasing a female and perching beside her as soon as he gets the chance. If she decides to take things further, she crouches, ruffles her body feathers and shivers her wings while the male excitedly circles around her. Then she lifts her tail and exposes her cloaca which looks like a little pink bead. The male gives it a sharp peck. Her cloaca begins to throb and may extrude a tiny white droplet which the male inspects intently. It is sperm that has resulted from a previous mating. Only when this has dropped off will he mount and give his sperm to her.

Infidelity between paired male and female reaches an even greater extreme among populations of one of Australia’s most colourful birds, the superb fairywren. The male has a shining sapphire-blue head with a glossy jet-black patch on the back of his neck which extends into a bar around his eye. The female, like so many others, is a plain brown. The bush country where the fairywrens live not only contains little food but is poor in nest sites. Young birds tend to stay in the territories where they were hatched and to take over the nest site when one of their parents dies. So fairywren pairs are nearly always closely related – father and daughter, brother and sister, mother and son. Incest brings the dangers of weakening the stock genetically. The fairywrens, however, manage to reduce this by making their pair bond highly elastic. Both male and female seek nearly all their matings outside it. A philandering male regularly visits other territories and shows off his brilliant plumage in a series of flirting displays. Sometimes he will add to his already considerable glamour by carrying a flower in his beak. He only presents such bouquets to females other than his long-term partner with whom he has established a nest. Using such wiles, he may copulate with as many as ten different mates in a season. Similarly, the female may do so with up to six different males and allow her regular partner only just enough matings to keep him feeding the family they have in their nest. The fact is, however, that none of the chicks in that nest may be his. For fairywrens, the pair bond has become little more than a social convenience.

For one bird, remarkably, it has disappeared altogether. The aquatic warbler lives in the wetlands of eastern Europe. During the summer, the birds forage in the grasslands surrounding their swamp. Here, the female aquatic warbler searches for a mate. When she finds him, they copulate but this act, far from being momentary, may last for up to half an hour. The male has huge testes and immense sperm stores and he is able to inseminate her seven or eight times during this one coupling. As a result, her reproductive system is flooded by his sperm ensuring that the egg she is about to produce will almost certainly be his. After they separate, she goes back to the nest she has constructed for herself and within the next few hours lays one egg. The next day, however, she goes in search of another male. So she continues until her clutch of up to six eggs is complete. Every one of them is almost certainly from a different father.

The production of an egg has demanded much from both parents. Both male and female have done their best to select the best partner they can find and to contribute to as many fertile eggs as possible. But much more labour will now be needed if that egg is to hatch and the young to be reared.