The Lyrebird's Borrowed Voice

In a wet Victorian rainforest a male superb lyrebird opens his beak and produces the precise mechanical whine of a chainsaw, then the rhythmic blast of a car alarm, then the rapid-fire motor drive of a camera shutter, all in sequence, all from one throat.

A throat that mirrors the forest

The behaviour is not rare, and it is not embellished in the retelling. Roughly 70 to 80 percent of everything an adult male superb lyrebird sings is a direct imitation of something else, drawn from the calls of other birds and from whatever else has passed through the gully he lives in. The accuracy is hard to overstate. In one documented case, a wild lyrebird's laughing-kookaburra impression was so faithful that a real kookaburra answered him back, the model unable to distinguish the copy from the original.

Narrating the BBC series The Life of Birds in 1998, David Attenborough described the lyrebird's vocal repertoire as "the most elaborate, the most complex, and the most beautiful" in the animal kingdom. The superlative lands differently once you realise the voice earning it is almost entirely borrowed.

Where the bird actually lives

The superb lyrebird, Menura novaehollandiae, was given that name by the ornithologist John Latham in 1801, one year after Major-General Thomas Davies presented the first known specimen to the Linnean Society of London on 4 November 1800, under the name Menura superba. The genus name comes from the Ancient Greek mene, meaning moon, and oura, meaning tail, a reference to the transparent crescent-shaped lunules on the outer tail feathers.

It is endemic to southeastern Australia, ranging from southern Victoria up into southeastern Queensland and occupying both subtropical and temperate rainforest and the brighter, more open wet and dry sclerophyll forest. Between 1934 and 1954, during an era of widespread land clearing, a second population was released in southern Tasmania as insurance against habitat loss on the mainland. That introduced population is now thriving and even growing.

The species is listed as Least Concern by the IUCN, with the most recent assessment dated 12 November 2021. The label is reassuring on its own, but the bird's slow reproduction, a single egg per breeding season incubated for up to seven weeks by the female alone, leaves local populations exposed to any sustained disturbance of their forest corridors.

The voice box

The mechanism behind the mimicry sits at the base of the trachea, in the songbird voice box known as the syrinx. The lyrebird's syrinx carries more independently controlled muscles than that of any other songbird, which allows it to push air through the left and right sides of the airway separately and reproduce two overlapping sound sources at the same instant. Two voices, one throat, no audible seam.

This vocal hardware is paired with an unusually long physical investment. A male requires seven to nine years just to reach sexual maturity and grow his full ornamental display tail. The completed tail reaches up to 70 centimetres in length and is constructed of 16 specialised feathers: two outer S-shaped lyrates, twelve fine silvery filamentaries, and two silvery median feathers. For most of a decade, while the tail grows in, the male is also refining and sharpening the imitations he will eventually perform from the circular dirt mounds he scratches into the forest floor through the winter breeding season.

A single male's territory overlaps with the territories of up to six females, who visit him at his arenas. The accuracy that wins those visits is, by the research summarised in the literature, a direct factor. Females prefer males that produce more accurate mimicry and a greater diversity of mimetic songs in their repertoire.

Sounds that outlive their source

The strangest fact about the lyrebird's library is that it is not built from the originals. Juvenile lyrebirds do not learn their mimicry directly from the model species. They learn it from older lyrebirds, a copy of a copy of a copy, with the consequence that an imitation can persist in a local population for decades after the original sound has vanished from the forest. A chainsaw heard in a Victorian gully in the 1980s can still ring out there long after the loggers have packed up and left.

In 2013 the National Film and Sound Archive added a wild lyrebird recording to the Sounds of Australia registry. The audio features the bird reproducing workmen, chainsaws, and the electronic alert tones of a children's shooting game. The recording is, in effect, a memory of a moment in human noise, lodged in the throat of a bird and then handed forward to the next generation. Some populations in the New England region of New South Wales carry a flute-like timbre in their songs that is heard nowhere else, a culturally transmitted local dialect rather than an individual quirk.

The anatomy that makes this transmission possible is far older than any of the sounds it now archives. Fossils referred to the family Menuridae from the Riversleigh deposits in Queensland date to roughly 15 million years ago, in the early Miocene. The voice box that today renders a chainsaw with surgical precision was already in place tens of millions of years before chainsaws, motors, or shutters existed.

The architect on the forest floor

While the lyrebird dominates the canopy with sound, it lives most of its life on the ground. Its diet is dominated by invertebrates: earthworms, insects, spiders, centipedes, taken from the upper soil layers. The foraging is not delicate. A single bird can disturb and bury up to 200 tonnes of leaf litter and topsoil per hectare per year, accelerating nutrient cycling and reducing the dry fuel load that would otherwise feed bushfires. The forest's most exacting acoustic archivist also happens to be one of its hardest-working physical architects.

The paradox is that all of this elaborate apparatus, the ancient syrinx, the decade-long maturation, the sixteen-feathered tail, the dirt mounds, serves a voice that does not, in the strict sense, belong to the bird that performs it. The male stands on a mound he has scratched into the forest floor, fans his silver-white tail forward into a veil, and sings a repertoire he did not invent. He acts as a curator. The kookaburra. The bowerbird. The camera shutter. The chainsaw. The most elaborate voice in the animal kingdom turns out, on inspection, to be a sound archive, and the forest he lives in is more durable in his throat than it is in the air.

Sources

• Wikipedia: Superb lyrebird (Menura novaehollandiae)
• Wikipedia: Syrinx (bird anatomy)
• National Film and Sound Archive: Sounds of Australia