WASHINGTON (AP) — One of the great interspecies love stories of our time has come to an end.

Walnut, a white-naped crane and internet celebrity, has passed away at age 42. She is survived by eight chicks, the loving staff at the Smithsonian's National Zoo and Conservation Biology Institute, and by Chris Crowe, a human zookeeper whom Walnut regarded as her mate for nearly 20 years.

“Walnut was a unique individual with a vivacious personality,” Crowe said, in a statement released by the National Zoo. “I’ll always be grateful for her bond with me.”

The tale of Walnut (and Chris) has inspired internet fame and the occasional love song. It dates back to the bird's 2004 arrival at the institute's campus in Front Royal, Virginia.

The chick of two wild cranes who had been brought to the U.S. illegally and were later rescued by the International Crane Foundation, Walnut was hand-raised by people and bonded with her human caretakers. That preference continued when she came to the institute; she showed no interest in breeding and even attacked male crane suitors.

But white-naped cranes are considered vulnerable by the International Union for Conservation of Nature. Today, less than 5,300 remain in their native habitats in Mongolia, Siberia, Korea, Japan and China due to habitat loss, pollution, nest predation and poaching. And as the offspring of two wild-caught cranes, Walnut’s genes were not represented in U.S. zoos. So convincing Walnut to breed was regarded as a priority.

In stepped Crowe, who, according to a zoo statement, won her over by “observing and mimicking" the institute’s male white-naped cranes' actions during breeding season.

Videos show Crowe offering Walnut food as well as grass and leaves for nest-building materials. When he flaps his arms in front of her, the tall majestic bird flaps excitedly in response and dances in a half-circle with her head bobbing. Once Crowe had gained her trust, he was able to artificially inseminate her using sperm from a male crane.

The unique arrangement proved wildly successful and Walnut has given birth to eight chicks. The fertilized eggs were given to other white-napped crane pairs who tended to them as their own. Of the eight white-napped cranes currently living at the institute, one is Walnut's chick and another is her grand-chick.

The relationship also seems to have been beneficial for Walnut's health; at 42, she nearly tripled the median life expectancy of 15 years for white-naped cranes in human care.

Walnut was born in Wisconsin in the summer of 1981. She was named after a local Wisconsin restaurant’s popular walnut pie dessert.

Starting on the morning of Jan. 2, keepers noticed that Walnut wasn't eating or drinking. Not even offers of her favorite treats — frozen-thawed mice, peanuts and mealworms — couldn't spark her appetite. Veterinarians administered fluids and antibiotics and drew blood for analysis. But her health continued to decline and Walnut was eventually hospitalized. She passed away peacefully, surrounded by an animal care team; an autopsy revealed the cause of death to be renal failure.

“She was always confident in expressing herself, an eager and excellent dancer, and stoic in the face of life’s challenges," Crowe said. "Walnut’s extraordinary story has helped bring attention to her vulnerable species’ plight. I hope that everyone who was touched by her story understands that her species’ survival depends on our ability and desire to protect wetland habitats.”

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