In January, 16-year-old western lowland gorillas Layla and Kumi each gave birth to a new baby, both fathered by 32-year-old Ernie, at the Bronx Zoo. This is the second pair of gorillas born at the zoo in just over a year, and brings the total population of The Congo Gorilla Forest up to 19—the largest in North America—spread about among two breeding troops and one young males troop.

The zoo, which has now welcomed 52 gorilla births since 1972, participates in the Species Survival Plan, a cooperative breeding program designed to enhance the genetic viability of animal populations in zoos. This is important for western lowland gorillas, which are designated as Critically Endangered by the International Union for Conservation of Nature (IUCN).

The sex of the new additions is not yet known, but the babies, who weighed just 4 to 5 pounds at birth, have a lot of growing to do. If they are males they’ll reach 350 to 450 pounds and stand up 6 feet tall; if they’re females they’ll top out at 150 to 250 pounds and 4 feet.

Check out video of the adorable babies below and visit the zoo to catch them in action.

All photos courtesy Julie Larsen Maher © Wildlife Conservation Society