Secrets of the Whales premieres on Disney+ on Thursday, April 22
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Sigourney Weaver delivers a moving narration in the upcoming Disney+ series Secrets of the Whales.

In a PEOPLE exclusive clip, Weaver narrates National Geographic explorer and photographer Brian Skerry's observation of a family of orcas in the deep seas.

"The next generation is growing up with new traditions but it can come at a heavy cost," she says.

Skerry explains seeing a family of orcas and a mother orca "carrying a dead calf and pushing it through the water," as Weaver's voice narrates that a mother orca "may stay with her dead infant for days, even weeks."

"It speaks to the complexity of these animals and their culture. They are very sentient beings, they're highly evolved," Skerry says in the clip. "They possess cultures that we don't fully understand."

The series took over three years to film as filmmakers, including Skerry, traveled to 24 locations to learn from the world's largest marine mammals. 

Secrets of the Whales, Sigourney Weaver
Credit: Disney+; Anthony Harvey/Getty

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Executive produced by Weaver's Avatar and Aliens director James Cameron, the series explores relationships within whale communities, including several firsts such as evidence suggesting beluga whales give themselves names so groups can keep track of each other.

Along with the series, National Geographic has also released Skerry's book Secrets of the Whales, which is on sale now.

The National Geographic four-part special premieres on Earth Day, April 22 on Disney+.