Great Argus

Charles Darwin devoted several pages of "The Descent of Man" to the great argus's wing feathers as some of his strongest evidence for sexual selection — the idea that female mate choice can drive the evolution of elaborate, otherwise useless male ornaments. What impressed him was not just that the feathers carry rows of eyespots, but that each spot is delicately shaded from pale on one side to dark on the other, exactly as a real three-dimensional ball lit from above would be shaded, producing a convincing illusion of solidity. Darwin argued that such precise, artistic-looking gradation could only have arisen through countless generations of females preferring slightly better "ball-and-socket" spots, since the pattern serves no survival purpose and in fact burdens the bird.

Barely, and reluctantly. The male's inner wing feathers are so enormously elongated and broadened, for display, that they compromise the wing as a flight surface; a male can flutter up to a low roost or escape a short distance but is essentially a ground bird. Females, which lack the extreme feathers, fly better but still spend nearly all their time on the forest floor. Great argus of both sexes walk everywhere, forage on the ground, nest on or near the ground, and roost in trees at night by clambering and short flapping hops rather than true flight. This is why intact, connected forest matters so much to them — they cannot easily cross clearings or gaps.

The male first prepares a "dancing ground" — a cleared, swept patch of bare earth a few metres across, usually on a ridge or hilltop, which he maintains for years and defends. From it he gives loud, ringing calls, especially around dawn and on moonlit nights, to draw females through the forest. When a female arrives and approaches, he begins a dance, and at the climax he throws both wings vertically upward and forward and spreads them into two gigantic overlapping fans, each covered in the shaded eyespots, so that he is almost completely hidden behind a wall of "eyes." His small real head peeps at the female through the narrow gap where the wings meet. He may also stamp, circle, and lower the fans and raise them again.

It is listed as Vulnerable and declining. It depends on large areas of tall, undisturbed lowland and hill rainforest in the Malay Peninsula, Sumatra, and Borneo — the same forest type that has been cleared faster than almost any other on Earth for oil palm plantations, timber, and pulpwood. Because the bird is a poor flier tied to the ground, forest fragmentation isolates populations that cannot easily recolonise. On top of habitat loss, great argus are snared and hunted for their meat and for the spectacular wing and tail feathers, and are caught for the cage-bird trade. Protected areas across Sundaland hold the main remaining populations.