Description
New Zealand wrens are tiny birds; the Rifleman being the smallest of New Zealand's birds. Their length ranges from 7 cm to 10 cm, and their weight from as little as 5-7g for the Rifleman to an estimated 50g for the extinct Stout-legged Wren. The South Island Wren (and probably the Bush Wren) weighs between 14-22g, and the extinct Long-billed Wren around 30g.
The plumage of the New Zealand wrens is only known for the four species seen by European scientists. All these species have dull green and brown plumage, and all except the Stephens Island Wren have a prominent supercilium above the eye. The plumages of males and females were alike in the Stephens Island Wren and the Bush Wren; the Rock Wren shows slight sexual dimorphism in its plumage and differences between the plumage of Riflemen are prononced, with the male having bright green upperparts and the female being duller and browner.
Both the Rock Wren and the Rifleman also show sexual dimorphism in size, unusually for passerines it is the female that is larger than the male. The female Rifleman also exhibits other differences from the male, having a slightly more upturned bill than the male and a larger hind claw.
The New Zealand wrens evolved in the absence of mammals for many millions of years, and the family was losing the ability to fly. Three species are thought to have lost the power of flight, the Stout-legged Wren, the Long-billed Wren and the Stephens Island Wren. The skeletons of these species have massively reduced keels in the sternum, and the flight feathers of the Stephens Island Wren also indicate flightlessness. Contemporary accounts of the Stephens Island Wrens describe the species as scurrying on the ground rather than flying.
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