NEW YORK -- A New York City zoo is celebrating the arrivals of two baby western lowland gorillas.

They're the first gorillas born at the Wildlife Conservation Society's Bronx Zoo since 2006.

Zoo officials said Thursday the babies' genders aren't yet known.

A gorilla named Julia gave birth on March 10. Another named Tuti had her baby on April 17.

Newborns weigh around 5 pounds (2.25 kilograms). Females could grow up to weigh 250 pounds (115 kilograms), males about 450 pounds (200 kilograms).

Gorilla infants are held by their mothers for the first four months of their lives.

Zoo visitors can see the babies this spring if conditions such as the weather and temperature are right.