2 Sumatran tiger cubs, a critically endangered species, born at National Zoo

WASHINGTON The National Zoo is celebrating the birth of a pair of Sumatran tiger cubs, a critically endangered species.

The zoo announced Thursday that the cubs born to 4-year-old Damai on Monday appear to be healthy and the new mother has been seen grooming and nursing them.

This is Damai's first litter, sired by 12-year-old Kavi. Damai arrived at the zoo in 2011 from the San Diego Zoo and Kavi came a year ago from Zoo Atlanta.

The zoo confirmed Damai's pregnancy in June through an ultrasound after she gained weight and exhibited behaviors indicating she could be pregnant.

Damai is being remotely monitored to allow her to bond with her cubs. The cubs won't be exhibited for several months, but fans can watch them on webcams.

"It's taken more than two years of perseverance getting to know Damai and Kavi and letting them get to know each other so that we could reach this celebratory moment," Craig Saffoe, a National Zoo biologist, said in a news release on the zoo's website. "Damai came to us as a young tiger herself, so it's really special to see her become a great mom."

The number of Sumatran tigers, the world's most critically endangered tiger subspecies, dwindled to about 400 from around 1,000 in the 1970s due to forest destruction and poaching, the Associated Press reported last year. Few Sumatran tigers have been bred in captivity.