BOSTON (AP) — The Franklin Park Zoo family has grown by two after officials there say a ring-tailed lemur recently gave birth to twins.

Zoo officials say the gender of twins isn't known yet, but they are active and their mother Nebbie is doing everything she should to care for them.

Nebbie gave birth on March 21 inside the zoo's Tropical Forest, bringing the number of lemurs on exhibit there to 10.

The births are connected with an inter-zoo species survival plan for lemurs, a program to maintain a genetically diverse and demographically stable captive population of the small primates.

Ring-tailed lemurs are listed as a vulnerable species in their native Madagascar.