RACINE, Wis. (CBS 58) -- The Racine Zoo has welcomed another pair of tamarin twins! 

The zoo announced the twins were born Sept. 15, 15 months after their older siblings, Tomasso and Tonetta, were born last summer. 

According to the zoo, animal care staff had been suspicious of a possible pregnancy and an ultrasound confirmed their suspicions a few weeks before Amelie gave birth. 

Though the birth frequency can seem fast to humans, the zoo says it's not uncommon for emperor tamarins. Mom Amelie has had babies six months apart in the past, according to the zoo. 

These twins are the 9th and 10th offspring of Amelie and her mate, Pitino. This also makes a total of 18 emperor tamarins born at the Racine Zoo since 2014, including the mother, Amelie, who was born in 2017.

The Racine Zoo is a partner of the Species Survival Plan for emperor tamarins, and tamarins that were born at Racine Zoo are now living in zoos all across the country, from Arizona and Texas to Pennsylvania and New Jersey.

“I am very proud of the Racine Zoo and its ability to contribute to the long-term survivability of this species. The Animal Care staff at Racine Zoo are very adept at their care and breeding,” said Dan Powell, the Curator of Animal Care and Conservation at Racine Zoo.

The twins are still very small at barely 6 weeks of age. They can typically be found riding around on either their dad or their siblings’ backs, because in tamarin families, all members help with infant care.

Once confirmed, the gender of the babies will be revealed on the Zoo’s social media pages. If you want to see the cute little faces, the family can be seen in the zoo’s Vanishing Kingdom building every day from 10 a.m. to 4 p.m.