Ground-breaking reintroduction for Cabo Verde's most threatened bird

6 Jul 2018

Great escape: After years of preparation, the Raso Lark (Critically Endangered) now spreads its wings on its new home of Santa Luzia – video below

By Shaun Hurrell

Approach Raso by boat and it can look like the foundations of a prison: a ten-metre-high perimeter wall of seemingly impenetrable reddish volcanic rock rises from a 'moat' of turbulent, shark-patrolled, Atlantic water. But rather than tall turrets and defensive battlements, the only human infrastructure on this mostly flat little island is an ex-military tent; rather than guards carrying guns, instead one might spot conservation biologists programming radio tags through the wind-torn gaps in the tent’s canvas.

Who, then, are the ‘prisoners’? Raso Larks Alauda razae (Critically Endangered), some of the rarest birds in the world. For many decades this little brown, crested bird has been confined to Ilhéu Raso (Raso Islet), a mere seven square kilometres of barren rock in Cabo Verde, off the west coast of Africa. The ‘crime’? It’s a complicated case of injustice: the Raso Lark is an innocent victim of the human introduction of invasive predators.

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A new home for Raso Lark

19/05/2018

In a bid to preserve its threatened population, the Critically Endangered Raso Lark has been reintroduced to an island from which it has been missing for centuries.

Raso Lark's range has been restricted to the small islet of Raso, Cape Verde, since humans arrived in the archipelago in the 15th century. Raso is largely a rock desert, with some sandy parts in the west, and the larks generally favour small vegetated areas along dry stream beds on level plains with volcanic soil. The tiny size of the island, plus its susceptibility to periods of drought, places Raso Lark in a precarious position. The species' population fluctuates greatly in response to climatic conditions; during wetter weather, when vegetation grows and food becomes plentiful, it can rapidly increase, with numbers in the low thousands, but drier periods have reduced its population to just a few hundred mature individuals in the space of a few years.

Prior to human colonisation, Raso Lark was believed to be more widespread, frequenting both Branco and São Vicente Islands. Evidence from subfossil bone deposits reveal that it once also existed on the islands of Santa Luzia, São Vicente and Santo Antão. There are also one or two recent records of vagrants from São Nicolau, including one at Ponta do Barril in March 2009.

With this in mind, a new project, Cape Verde conservation charity Biosfera 1, in association with the Portuguese Society for the Study of Birds (SPEA) and other organisations, has launched an ambitious reintroduction programme on Santa Luzia.

Since 15 April, a total of 37 Raso Larks were translocated from Raso to Santa Luiza, where they have been successfully released. Each individual lark has been fitted with a small radio tag so that it can be tracked, allowing researchers to establish which area of the island they favour and whether the birds stick together and behave naturally.

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