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Larks Ascending

last modified Jul 04, 2013 03:09 PM
The Critically Endangered Raso lark (Alauda razae) lives on a single desert island of 7 km2 in the Cape Verdes off West Africa. Happily, the birds have undergone a remarkable boom over the past decade, according to a paper published online this week in Animal Conservation.

 

Since 2004, the world population of the birds has skyrocketed from 65 to 1490—including a tripling in numbers last year alone—according to a team led by ornithologist Michael Brooke of the Department of Zoology, University of Cambridge. "It's unprecedented among birds," Brooke says. The increase correlates with greater rainfall, which probably boosts the number of insects available to eat.

When the population was at its nadir in 2004, there were just 20 females, and about 45 males. This sex ratio bias arose because of consistently higher female mortality. Since then, the annual visits, also involving Tom Flower and Justin Welbergen of the Department of Zoology, have recorded not only a growing population but also a return to equal number of males and females. This happened because the young fledglings pumped into the population were equally likely to be male or female.

Andy Symes of BirdLife International, who has reviewed the conservation status of the lark, calls the finding "fantastic news." But he cautions that the population could easily fall if the island dries out again. Both he and Brooke recommend that a second population be established on a nearby island to help ensure that the species isn't wiped out by an unlucky event such as severe drought, disease, or new predators.

Rainfall-related population growth and adult sex ratio change in the Critically Endangered Raso lark (Alauda razae). Animal Conservation.

Science 13 April 2012: Vol. 336 no. 6078 pp. 136-138.