Smallest perching bird’s long-lost family revealed by genetics


James Eaton/Birdtour Asia By Brian Owens Species: Pygmy Bushtit (Psaltria exilis) Habitat: Mountainous forests of western Java, Indonesia The pygmy bushtit’s diminutive size makes it a superlative species, and it has a genus all to itself. But now genetics is showing that it’s not so special after all. The pygmy bushtit isn’t much to look at. It’s an inconspicuous dull grey, but it is absolutely tiny. So small in fact, that it is the smallest member of the Passeriformes, or perching birds, an order that encompasses more than half of all bird species including sparrows, finches and chickadees. A typical pygmy bushtit has a body about the size of your thumb, but if you include its tail, it measures a heady 8 centimetres long. It’s not the smallest bird though – some hummingbirds, for example, are tinier. Other long-tailed tits and bushtits are temperate birds, but the pygmy bushtit lives only in the western part of the Indonesian island of Java, in tropical open forests and plantations above 1000 metres. Because of that geographical isolation, the pygmy bushtit was thought to be the only bird within its Psaltria genus and only distantly related to other tits. But Ulf Johansson, a zoologist at the Swedish Museum of Natural History, and his colleagues have now analysed the genetics of the Pygmy Bushtit using a museum specimen collected in 1920. “We know very little about this bird,” he says. “It looks and behaves very much like other long-tailed tits and bushtits, but no one had tested it,” Johansson says. They found that it’s not so genetically isolated after all. It belongs in a group of long-tailed tits, and is most closely related to the black-throated bushtit, which lives throughout the Himalayas and eastern Asia as far south as Vietnam. The genetic links indicate that the species were separated only some 2 million years ago, and the pygmy bushtit changed its look rapidly – shrinking in size and losing the distinctive black and white face markings and bright orange cap sported by its cousin. Johansson isn’t surprised by the result – he thinks the new family tree makes more sense now than it did before. “Java is a relatively young island, after all, only about 2-3 million years old,” he says. “So it can’t have been isolated that long.” The findings mean that the pygmy bushtit is likely to lose its unique genus name, and instead join the black-throated bushtit in the Aegithalos genus. Journal reference: Ibis, DOI: 10.1111/ibi.12377 Read more: Minimals: Meet the smallest critters of all More on these topics:
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