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Breeding season changes in physical appearance can involve more than a set of new feathers. Bill color and shape can alter, for example, as in the Atlantic puffin (Fratercula arctica), the sexes of which look very alike. In early spring, in addition to assuming a crisper and more starkly contrasted plumage, the bills of both male and female are transformed by the growth of brightly colored external plates. The enhanced bills—the harlequin color of which may explain one of the bird’s traditional names, ‘sea parrot’—form a central part of the elaborate pair bonding and display sequences in which puffins engage, with the bill plates shed after breeding. Other birds that assume similar bill adornments include the males of duck species such as the king eider (Somateria spectabilis), with other waterfowl males developing a fleshy knob-like protruberance at the bill base.
Other features such as facial wattles or lappets, eye-combs, inflatable throat sacs and brightly colored bare lores (the area between the eyes and bill) are all used by male birds in combination with various forms of locomotion and posturing to impress females. Male prairie-chickens sport bright yellow eye-combs and orange neck pouches, for example, while the male magnificent frigatebird (Fregata magnificens) has an un-missable red throat pouch, which he inflates like a balloon and uses as a beacon to attract females.
For sheer physical impact, however, there are few species to beat the wild turkey (Meleagris gallopavo). Almost every part of a mature male in breeding condition is calculated to command attention. The featherless head and neck are covered in fleshy caruncles, with wattles dangling from the neck and the bill partly obscured by a fleshy flap of skin called a snood. When the bird is excited, the bare skin, wattles, and snood become engorged with blood and the head undergoes color changes. Blue signifies sexual arousal, red aggression. The body feathers are puffed up and out, maximizing the appearance of bulk, the tail is fanned out into a semi-circular arrangement, and the wings are dropped slightly, creating the impression of an enormous feathered ball.
Some of the most extreme forms of wattle are found on bellbirds, four species of which live in the forests of Central and South America, with all noted for their loud, clanging calls. The male three-wattled bellbird (Procnias tricarunculata) has three worm-shaped wattles issuing from the base of his upper mandible; these hang loosely down and are shaken vigorously during courtship. Other forms of watte are inflatable and serve to amplify courtship calls: the long-wattled umbrellabird (Cephalopterus penduliger) has a single feathered wattle of up to 14 inches long and, like other members of its genus, a parasol of feathers on its heat that is ‘put up’ when the bird is aroused.
Exotic breeding garb is most often found in males that do not assist the female much, if at all, in subsequent incubation and care of the chicks. Eye-catchingly colorful plumage would draw unwanted attention to the nest, so males that participate in parental care are often duller and more female-like than males that do not provide help to the female. Even for the brightest males, however, their finery is often only a temporary arrangement. Once the young have fled the nest, metaphorically or otherwise, most adult birds undergo a complete molt, regaining their basic plumage and in most cases—though not all—shedding special features such as bill plates.
In cases where the sexes look markedly different during the breeding season this period usually sees the male assume an appearance more akin to the female, although the situation varies widely. Ducks, for example, enter what is known as the eclipse stage, a total molt where even the flight feathers are shed, rendering the birds flightless for several weeks. It is all a world away from their pristine appearance only a few weeks previously.
Excerpted from The Mating Lives of Birds, by James Parry, MIT Book Press, Copyright 2012 James Parry/New Holland Publishers Ltd.