Stephens Island Wren or Lyall’s Wren – The smallest flightless bird ever
This may well be the Inaccessible Island rail which is still alive today, but there is one extinct species known to have been smaller which is reputed to have been flightless. This was the 10 cm (3.93 in) Stephens Island wren (Traversia (Xenicus) Iyalli), a New Zealand endemic of the family Xenicidae, which has three surviving members.
Unfortunately, hardly anything is known about this mysterious bird as it became extinct almost as soon as it was discovered in 1894. The only observations of it alive were by the lighthouse keeper, who saw it just twice in the evening, when, disturbed from holes in the rocks, it apparently scurried around on the ground like a mouse. It was never seen to fly.
About a dozen specimens were collected, but the species was rapidly wiped out by the lighthouse keeper’s cat as there had been no natural predators for the bird to adapt to.
Its bone structure and short, rounded wings suggest weak flight, as does its soft plumage, and if it was flightless then it would have been the only flightless passerine ever known. Sub-fossil bones found in the North Island and believed to be of Traversia indicate that the species was once more widespread.