India, Jan. 21 -- Geneva (dpa) - Zoos are facing ageing populations that threaten the conservation of endangered species, and targeted culls may be needed to make room for young animals, the team led by Marcus Clauss at the University of Zurich has warned. "If I could constantly build new enclosures, this measure would probably not be necessary," Clauss told dpa. "But if I keep all animals into old age in a world with limited enclosure space, I have no room for the next generation." The researchers examined 774 mammal populations, from hoofed animals to primates and carnivores, in European and North American zoos over 53 years. Across species, they found more populations with older than younger animals. They said the average age has steadil...