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The genus Ptiloris consists of four allopatric species of birds in the family Paradisaeidae. These birds of paradise are commonly known as riflebirds, so named for the likeness of their black velvety plumage to the uniform of the Rifle Brigade. Alternatively, the bird's cry is similar to a rifle being fired and hitting its target but a call like this is not commonly reported (see Behaviour and Ecology). They are distributed in the rainforests of New Guinea and Eastern Australia.
The genus is part of the bird-of-paradise family, Paradisaeidae, in the order Passeriformes (songbirds). The four species are the magnificent riflebird ( P. magnifica (Vieillot 1819) – magnificent or splendid), growling riflebird ( P. intercedens Sharpe 1882 – referring to its distribution between the two subspecies of P. magnifica), paradise riflebird ( P. paradisea, Swainson 1825 – paradise) and Victoria's riflebird ( P. victoriae Gould 1849 – after Queen Victoria). Two subspecies of P. magnifica are recognised: P. m. magnifica (Vieillot 1819) and P. m. alberti Elliot 1871; the growling riflebird is often considered a subspecies of P. magnifica as well. The subspecies have been named on the basis of distribution (see Habitat and Distribution), male attention-attracting call (see Behaviour and Ecology), and cladistic analysis.
The birds of paradise are thought to have originated 24–30 million years ago and belong to the radiation of passerines that occurred in Australia during the last 60 million years. As Australia become more arid over the last several million years, the birds of paradise withdrew to the regional rainforests of New Guinea and eastern Australia. Ptiloris arose from this residual stock in Australia, from which one member ( P. magnifica) has since spread to New Guinea. The separation in time of the Australian and the New Guinea P. magnifica determined genetically corresponds to the separation of Australia and New Guinea geographically (i.e. Torres Strait).
| Magnificent riflebird | Ptiloris magnificus | western New Guinea and the northern Cape York Peninsula. | |
| Growling riflebird or eastern riflebird | Ptiloris intercedens | easternmost Papua New Guinea | |
| Paradise riflebird | Ptiloris paradiseus | New South Wales and central Queensland | |
| Victoria's riflebird | Ptiloris victoriae | northeastern Queensland, Australia | |
Adult male riflebirds of the four species are similar in appearance: all are entirely velvety black with lighter underparts, iridescence on the head, upper throat and centre of the tail, and yellow mouth and gape. The iridescence on the paradise riflebird is blue, on Victoria's riflebird blue-green, and on the magnificent and growling riflebirds are green, blue, and purple. Males of the magnificent and growling riflebirds have more prominent grey-black underparts, black and yellow bands across their mid-breast, and long thin curved plumes from the lower flanks that extend to the end of the tail in P. magnifica or just short in P. intercedens.
Adult female riflebirds of the four species are also similar in appearance: all are largely brown above, have a prominent cream supercilium, and are whitish to buff with dark markings underneath. Female magnificent and growling riflebirds have thin blackish barring underneath, while paradise and Victoria's riflebirds have brown chevrons. Immature riflebirds resemble adult female birds and males do not achieve their full adult plumage until they are four to five years old.
The four riflebird species are separated geographically, an easy characteristic for field identification. Magnificent riflebirds are found on the Cape York Peninsula in Queensland, Australia ( P. m. alberti) and the lowlands and foothills of western New Guinea ( P. m. magnifica), while growling riflebirds are found in the lowlands and foothills of eastern New Guinea. Both species are largely absent from the highlands of New Guinea. Victoria's riflebirds are found on the Atherton Tablelands of Queensland, Australia, from just south of Cooktown to just south of Townsville. Paradise riflebirds are found in southeast Queensland and northeast New South Wales, Australia. Riflebirds are widespread throughout their ranges.
When feeding their young, female riflebirds will catch proportionally more arthropods than fruit to supply their growing young with foods rich in proteins and lipids. This has also been suggested as the reason for female riflebirds having larger bills than males. Nestlings have been reported as being fed crickets, grasshoppers, spiders, cockroaches, centipedes, cicadas, woodlice, beetles, and insect larvae. Males may take proportionally more easily obtained and energy-rich fruit to allow them to display for longer.
Male riflebirds appear to rigidly follow a progression of vocalisations, postures, and movements when displaying to females. The first stage is to call from the display perch and expose their yellow gape to attract attention. Male paradise and Victoria's riflebirds make a sound like "yass," male magnificent riflebirds produce a series of low whistles, and male growling riflebirds make a growling sound (hence the name). Once a female arrives at the display site, the second stage involves the male turning to face the female, raising his wings above his head to form a circle, again exposing his gape, and raising and lowering his body on his legs. If a female approaches, the male begins the third display stage directly in front of the female described as an "alternate wing clap", lowering one wing and hiding his head behind the other and then switching from side to side in quick succession. At this stage, male magnificent and growling riflebirds may start hopping sideways along the display branch. A female riflebird signals her receptiveness by briefly fluttering her wings and the male hops onto her back before copulation. Immature males may attempt to display during the breeding season as well but they appear clumsy and uncoordinated, like they need to learn to display correctly.
Female riflebirds are solely responsible for nest construction, incubation, and feeding nestlings. They have also been observed defending their nests. The nests of Victoria's riflebirds may be parasitised by the Pacific koel ( Eudynamys orientalis). The nest is a well-concealed open cup structure of leaves and twigs, at least 100mm internal diameter, and lined with leaves, plant fibres, and rootlets. Victoria's riflebird usually lays two eggs each weighing approximately 10g on consecutive days, incubates the eggs for 18 to 19 days, and broods and feeds the nestlings for 13 to 15 days. Little is known about the incubation and nestling of paradise, magnificent, and growling riflebirds. Nestlings hatch naked with their eyes closed and stay on the nest until fledging (nidicolous). Victoria's riflebird nestlings are brooded for the first six to seven days until they open their eyes and can thermoregulate and they achieve pin-break on their primary and secondary feathers by day twelve. Nestlings are fed two to three times an hour, with the female away from the nest for longer with two nestlings. Victoria's riflebird fledglings become independent from their parent after 74 days, while this period is unknown for the other species.
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