Rote learning: a unique leaf-warbler discovered in Indonesia

27/12/2018

An unusual warbler discovered on a small Indonesian island as recently as 2004 has just been described as a new species of leaf warbler. Named Rote Leaf Warbler after the island in the Lesser Sundas where it was found, Phylloscopus rotiensis differs from all other species in the genus by its relatively long, tailorbird-like bill and distinctive coloration.

Although many islands in the region harbour breeding populations of leaf warblers, Rote Island – which lies south-west of Timor – was historically not known to have any. However, while birding on the Tapuafu peninsula in December 2004, Dr Colin Trainor from Australia's Charles Darwin University observed several warblers which were "frequent in woodlands and tropical dry forest" and uttered a "breezy, rising and falling whistle" not unlike that of Timor Leaf Warbler on the adjacent larger island of Timor.

Five years later Philippe Verbelen and Veerle Dossche visited Rote Island to observe and study the birds, and succeeded in making detailed observations and obtaining a series of photographs. Philippe noticed that the leaf warblers looked substantially distinct from any other Asian, African or European species with which he was familiar: "Alarm bells went off when we realised how strikingly different the bill shape and the coloration of the Rote bird were compared to all other leaf warblers." The long bill had a yellow-orange lower mandible, and additionally the undescribed warbler showed a broader and more yellow supercilium than in Timor Leaf Warbler, a more prominent yellow crown stripe, warmer yellow sides of the head and underparts, and an olive-green rather than olive-grey crown.

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