New Zealand's Wellington Zoo has more than doubled its population of endangered ring-tailed lemurs after its four females gave birth to twins, the zoo's primate manager said on Tuesday.Primate manager Lisa Ridley said given all four adult female lemurs were first-time mums, they were not sure whether they'd have success with breeding them.The population of ring-tailed lemurs, made famous by King Julien in the 2005 movie "Madagascar", is declining in the wild.One of the challenges is female ring-tailed lemurs are only sexually receptive for one or two days a year.Zeus would be used for breeding for a few more years before being replaced to prevent the genetic pool from becoming too small, Ridley said."