Washington (CNN) -- Rocky, the National Zoo's first whooping crane since 1923, has no "whoop."
"I haven't heard any little squeak or squawk or anything from him," National Zoo keeper Debi Talbott said. "I have no idea why he doesn't vocalize."
Rocky, who has been at the zoo less than two months, has a champion in Talbott. She has devoted 20 years to working with cranes but this is her first whooping crane. At five feet tall, with a wingspan of seven feet, the big white bird comes when she calls.
Rocky probably won't produce any offspring at least in part because he doesn't whoop.
"As a crane, if you can't vocalize, you can't do what we call 'unison calling' with a mate, which is so much a part of the breeding, the bond, the courtship," Talbott said. "Because cranes tend to pair for life, that's a huge part of their bonding."
Whooping cranes are an endangered species. There are 567 in both the wild and captivity in North America, according to the U.S. Fish and Wildlife Service's 2010 count, up from a low of 21 whooping cranes.
In his previous home in Ellie Schiller Homosassa Springs State Park in Florida, Rocky shared an enclosure with a female whooping crane named Peepers, park manager Art Yerian said.
Peepers had her eye on a wild whooping crane, Number 501, who migrated over the state park each year and always stopped to visit her. At first, staff tried to keep Number 501 away from Peepers.
But eventually, the staff at Homosassa Springs let true love take its course and allowed the wild bird to move in with Peepers permanently. His name was changed from Number 501 to Romeo.
Yerian said they put Rocky in an enclosure beside Peepers and Romeo. When Romeo made his unison calls to Peepers, Rocky would mimic Romeo's movements, without the sound. Rocky became a third wheel.
According to Yerian, Rocky had an infection as a young bird that left scarring on his trachea, so it is unlikely he will ever whoop.
Rocky was moved to Washington's National Zoo to be an educational ambassador for his species. So far, he is fitting right in.
Rocky can listen to three neighboring Stanley cranes squawk outside. If he goes in his shed, he can hear the classical music recordings Talbott plays for him. The zookeepers have noticed that he likes to stand near the shed's window, where Talbott believes Rocky likes to look at his reflection in the glass.
Except for his lack of whoop, he appears completely healthy and normal.
"Rocky is a very calm bird," Talbott said. "He's not aggressive like all my other cranes. So nice to be able to go in and feed him without having my hand pecked."
And even if he never makes a sound, Talbott has plans to improve other parts of his socialization. Pretty soon, she says she is going to go into his enclosure when no one is around and try to dance with him. Dancing is also one of the mating rituals of cranes.
"When we had the single Stanley crane down here, when she was all alone before she got a mate, I would go in and dance with her and she would dance with me and we would run around the yard and chase each other and dance and jump up and down and one day she produced an egg. So, I must have done a really good job," Talbott said. "I want to see if he will respond to dancing."