PITTSBURGH -- An adorable cub was born at the Pittsburgh Zoo and PPG Aquarium, but its mother has not been taking care of it. The cub is now under veterinarians' care and will be reintroduced to its mother on Tuesday.

Toma, the zoo’s Amur tiger, gave birth to a female cub on Mother's Day.

“She could not have planned her delivery any better—a baby on Mother’s Day,” said Dr. Barbara Baker, president and CEO. "However, we are very cautious to celebrate because, as with any birth, complications can arise. We are very concerned about this cub."

Up until 6 a.m. on Monday the baby was active and very vocal. Later Toma began leaving the cub for longer periods of time, and the staff noticed the cub was not as active and unusually quiet.

The keepers and veterinary staff immediately took the cub to the Animal Hospital where they warmed her up and gave her supportive care.

They plan to reintroduce her to mom on Tuesday.

The cub will be bottle-fed every four hours on Monday night, so it will be strong for the reintroduction.

In litter-bearing species, sometimes one cub may not be enough to stimulate the mother to produce milk.

"We are going to treat Toma to try to stimulate milk production. The staff will continue to keep an eye on her and her cub using the video camera inside the den” Baker said.

The next key milestones will be Toma’s acceptance of the cub and her willingness to take care of it. If the reintroduction is not successful, the Zoo Veterinary Department is already prepared with a hand-rearing protocol, bottles, nipples, and milk supplement.

The mortality rate of cubs both in the wild and in zoos is between 30 and 40 percent.

Toma has a better chance of success since she is a second-time mom. The new baby is Toma’s third surviving cub; she is already mom to 18-month-old Petya and Mara.

In August 2006, Toma delivered three cubs, but one did not survive due to birth defects. "Most litters are two to three cubs, but it is not unusual to just have one,” Baker said.

Amur tigers, more commonly known as Siberian tigers, are a critically endangered species, due to habitat destruction and the illegal fur trade. The birth of a tiger cub is extremely important to the population. There are currently only an estimated 400 Amur tigers in the wild and 190 Amur tigers managed in the Association of Zoos and Aquarium accredited zoos.

The baby’s father is Globus who arrived from the Bronx Zoo last year.

RAW VIDEO: New Tiger Cub Born At Pittsburgh Zoo