Happy birthday: TWIN baby tamarins, born at the Racine Zoo, turn ONE!

RACINE -- TWIN baby tamarins, born at the Racine Zoo, turned ONE on Tuesday, April 18th!

Avril and Francois weighed in at 1.4 and 1.7 ounces each at birth.

Emperor tamarins are primates known for their small size and signature long, white mustaches.

Elizabeth Heidorn, executive director of the Racine Zoo said the following in a news release after their birth:

"We couldn’t be more excited to welcome these two charismatic little primates to the world. We are proud to be one of two accredited institutions successfully breeding emperor tamarins in partnership with the Species Survival Plan (SSP). Every little bit we can do to help the species is critical."

Zoo officials said their mother, Isabella, acquired from Zoo New England, and their father, Marquis acquired from the San Francisco Zoo, have been paired in Racine since summer 2012. Unlike many fathers in the animal world, the male emperor tamarin is the primary caretaker. With the exception of nursing, the babies would have a solid grip on him at all times until they were about 70 days old.

Their first offspring, Cadeau, a female born in 2014, was moved to the Staten Island Zoo last September 2016 to be part of another breeding pair.

Isabella and Marquis again welcomed twins in February of 2017. These twins were born on February 24th.

In their post to social media, celebrating the first birthday of the twins born in 2016, zoo officials said: "This family just keeps growing and we couldn't be happier!"

Only the Racine Zoo and the Como Zoo in St. Paul, MN, has successfully bred this type of tamarin.