Zoo keepers are probing why a male Malayan tiger killed a four-year-old female tiger it had only just met, when they were brought together for breeding purposes in California. Connor, who was born at San Diego Zoo in 2011, was introduced to female Tiga Tahun on Saturday for their first mating session, and initially everything seemed to be going routinely. "Unfortunately this changed quickly and zookeepers were unable to separate the two animals," said zoo spokeswoman Jennifer Mehlow, explaining how the male tiger suddenly displayed "aggressive behavior." The female feline died of injuries to her neck and breathing ability inflicted by Connor, she said. The death occurred before the world-famous zoo opened, so no visitors witnessed the incident. It was the first fatal attack during a mating session at the zoo, although large carnivores often mix aggressive behavior with breeding interactions, sometimes leading to injury, the spokeswoman said. The Malayan tiger, who was born at the Bronx Zoo in New York, was brought to San Diego earlier this year for breeding purposes, in an effort to propagate the endangered species, Mehlow said. Tigers are normally solitary animals, and males and females only usually meet to mate when the female is in season, according to the Los Angeles Times, which said Connor is now the zoo's only Malayan tiger. The sub-species is listed as endangered because of poaching and loss of habitat in Malaysia and parts of Thailand where they are found, the newspaper said.