Introducing a New Giant River Otter to the Group

Introducing animals at the Zoo is a delicate process, which can be made even more challenging when introducing one of the most territorial animals on Earth.

In fall of 2022, we lost 12-year-old Arya after a months-long battle to cancer. During her battle with the disease, she received top notch care from our veterinary team that worked with oncologists at Penn Vet to give her the best treatment plan possible, including chemotherapy. Ultimately though, she tragically succumbed to the disease, leaving her long-time mate Matteo alone.

“This was a very stressful time for us, having lost a beloved otter and at the same time, brainstorming ways to ease Mateo into a temporary, solitary life was difficult,” said zoo keeper Ellie Caruso. “Even though we allowed Matteo to spend time with his mate Arya after her death, he still went through a stressful grieving period.”

Keepers, curators and veterinary staff knew that they would need to make the attempt to introduce Matteo to our brother and sister pair, Thor and Yeyuno, for his well-being.

Giant river otters are highly social and will form extended family groups structured around a dominant breeding pair and matriarch. Because of that, they can be very aggressive and territorial, too. In a zoo setting, this species is sometimes grouped by mate selection, where a young female chooses her mate from one or more bachelor males. Because Matteo was a dominant breeding male and Yeyuno never had a mate, the animal team hoped Yeyuno would accept him into her group with younger brother Thor.

There are standard steps for introducing any two new animals. First, the animals typically are able to smell and hear each other through a door or wall. Then, they are typically introduced through a mesh panel so they can see each other. If all goes well with the mesh panel or “howdy” phase, the animals are introduced.

Initial meetings between Matteo and Yeyuno and Thor were not hopeful. At the first “howdy” session, Thor was very aggressive, so the keeper team decided to end it quickly, but they didn’t give up. Using their past knowledge from introductions of other animals, the keepers decided they would only shut the door after positive interactions. So, if Thor and Matteo were aggressive, they waited until their aggressive behavior changed to friendlier behavior before ending the interaction.

“I wanted to try and end each door opening on a positive, even if it meant doing dozens of “peek a boo’s” a day, which is what we did,” said Caruso. “That paid off and allowed them to quiet down and get curious about each other.”

The team tried this approach for two days until there was a total shift in behavior: Matteo started showing dominant behavior to Thor! Yeyuno also showed she and Matteo were bonding—which is exactly what the team was hoping for.

“Their bonding caused the shift we needed. Thor was raised with two breeding parents and multiple siblings, so he understands that role in the family,” said Caruso. “We hoped if Matteo and Yeyuno formed a dominant breeding bond, Thor would fall back into his previous family role of submissive male to dominant male (his father).”

After this, keepers moved the otters to exhibits where they were able to interact through mesh the entire day. After several days showing positive behavior, they made the decision to fully introduce them.

When the moment came, the entire team was present. After days of hard work studying animal behavior, Matteo successfully joined Yeyuno and Matteo! You can now see all three otters swimming together when you visit Water is Life.

“This introduction was a true testament of our keepers’ incredible skill and knowledge,” said Curator of Carnivores and Ungulates Maggie Morse. “I am incredibly proud our team was able to successfully introduce our group. This was not only beneficial for our beloved Zoo but will give otter keepers all over the globe the knowledge to increase welfare for animals in the future.”

“It is so wonderful to see this family hierarchy play out. We can learn so much by just watching their group dynamic, which enables us to attempt and succeed at amazing moments like these!” said Caruso.

Philadelphia Zoo has a long history with giant river otters. In 2004, the Zoo became the first in North America to successfully breed this species with the birth of Primero. Since then, many of the giant river otters born at the Zoo have gone to other AZA institutions to continue the breeding of this species under the Species Survival Program (SSP).