PUERTO VALLARTA, Mexico (Reuters) - Keepers at a Mexican zoo are bottle-feeding round the clock after four big cats gave birth to nine cubs in two months, among them a rare white tiger. The owners of family-run Zoologico de Vallarta, set deep inside virgin jungle in the Pacific coast state of Jalisco, say there is no big secret behind the rash of births -- just a propitious natural environment and lots of hands-on care. "The zoo is magical. It's situated in such a precious area which is almost completely the animals' natural habitat, and that has a lot to do with why they procreate happily and naturally," said veterinarian Xochitl Nicteja, who is bottle-feeding the youngest cubs with milk every two hours. "If you observe the animals they are very comfortable. You can see they enjoy their habitat, and the love and care we give them, so the rest of it is up to them."