The Bronx Zoo in New York City has announced the birth of two gorillas, the first born at the facility since 2006.

The western lowland gorilla babies add to the ranks of the zoo's Congo Gorilla Forest, which now stands at 20 primates, the largest group of gorillas in North America.

In a statement released Thursday by the Wildlife Conservation Society (WCS), which oversees the Bronx Zoo and several other New York City wildlife facilities, the zoo said the pair of gorillas were born earlier this year to different mothers, but they share the same father.

One of the babies was born on March 10 to 33-year-old Julia, the second was born to 19-year-old Tuti on April 17. Each of the mother gorillas have given birth before. The gorillas' father, Ernie, is a first-time dad.

The sex of the newborn gorillas remains unknown. Infant gorillas are held by their mothers for the first four months of their life. The infants will begin eating solid food at around 6 months of age, but they will continue to nurse from their mothers until they are 3 or 4 years old, the zoo said.

In a video released by the WCS (below), the infants can be seen nursing and appear healthy.

Newborn gorillas are born weighing between 4 and 5 pounds. Gorilla gestation is typically 8.5 months. A fully grown male gorilla can weigh between 350-450 pounds and grow up to 6 feet tall; fully grown females are smaller, weighing between 150-250 pounds and standing up to 4 feet tall.

The International Union for the Conservation of Nature (IUCN) lists western lowland gorillas as critically endangered, having seen a population reduction of 80 percent in their natural range, which spans tropical and subtropical forests in equatorial Africa.

The two primary threats to gorillas in their natural environment are commercial hunting and the Ebola virus, according to the IUCN Red List.

The Bronx Zoo takes part in a gorilla breeding program to help ensure the survival of the species. Since opening in 1999, 15 gorillas have been born at the zoo's Congo Gorilla Forest, which spans 6.5 acres in the zoo's southwest corner.