Twin sea lions born at SeaWorld Orlando

Twin sea lions were born last week at SeaWorld Orlando.

A rarity in the animal world, the twin births are a first for the park.

Officials say the sea lions are healthy and are nursing from their mom, Fable, who is also doing well.

The pups will nurse until they are between six and 12 months old. Fable, who is nearly 14 years old, was also born at the Orlando park.

The first of the twins was born at 11 a.m. June 17, and the second followed a few hours later. The sex of the twins has not yet been determined.

Researchers at SeaWorld say they believe California sea lions are born after delayed implantation. It's triggered by the length of the day, so as to assure the pup  will be born when environmental conditions are optimal for its survival.