On April 21, three Amur tiger cubs were born at the Columbus Zoo and Aquarium in Powell, Ohio.

According to zoo staff, each tiger weighed 2.5 pounds (1.1 kilograms) at birth, which falls within the typical range of 1.5 to 3 pounds (0.7 to 1.4 kg) for tiger cubs.

The babies were monitored closely by an animal care team over a live video feed. The team rushed in to nurse and care for the baby cubs when their mother’s maternal instincts didn’t kick in.

The zoo officials said the cubs are now in an incubator. However they are now feeding vigorously and are already looking strong.

Caretakers at the zoo were concerned that the cubs' mother, 10-year-old Irisa, would never conceive. Harry Peachey, curator of Asia Quest at the Columbus Zoo said that at such an old age and with one undersized ovary, there were a number of strikes against her.

However, Irisa bred with 11-year-old Foli in early January. Foli has two other litters to his name, and has since been moved to another zoo, based on a recommendation by the Species Survival Plan, which manages populations of endangered species within most US zoos.

According to Peachey, at the end of last week, when Irisa was on the verge of going into labor, her behavior was abnormal. She stopped eating and refrained from moving into the den.

However, her birth went relatively smoothly even after days of this odd behavior. The first cub was born at 12:40 am local time, and the last arrived at about 2:23 am.

Peachey said, "She did nurse one cub, but she didn’t nurse the other two. And she wasn’t bringing them toward her. She wasn’t doing all the things that we regard as normal maternal behavior".