Walnut was born in a species-recovery breeding program in the 1980′s.  The program had crane chicks hand-raised by human volunteers, and at that time they did not fully understand the measures necessary make sure that the chicks do not imprint on humans and retain their identity as cranes.  

As a result, her keepers believe, Walnut does not recognize other cranes as members of her own species.  

It has not been proven that Walnut killed her previous suitors; however, there is a persistent rumor in the white-naped-crane-conservation community that she did.  

Because this species is highly endangered, and the gene pool of the captive population is small, it’s pretty important for the survival of her species that Walnut A) mate, and B) not kill a bunch of other cranes.  

The actual name of the keeper is Chris Crowe.

They both arrived at the Smithsonian Conservation Biology Institute in 2004.   

Walnut immediately began paying special attention to Chris--and ignoring the eligible male crane in a nearby enclosure.  

Walnut initiated their courtship, performing the opening moves of a mating dance.  

Chris realized that if he reciprocated the mating dance, it might be possible to artificially inseminate Walnut with her participation and consent.  (The process normally involves restraining the bird.)  

It worked!  

Chris and Walnut have had five children, who were raised by other crane couples at the facility--sometimes the biological dad and his mate--both because it’s unclear whether Walnut would accept the chicks as her own, and because Chris is not equipped to be a Crane Dad.  

However, the Institute provides her with artificial eggs to sit on, and Chris takes his turn looking after them.  (This would not work with real eggs because he can’t sit on them properly, but Walnut seems to feel that he is on the job if he just stands over them.)

she has not been PROVEN to have killed her exes, but there is a PERSISTENT RUMOR (really officers she's simply DEVASTATED, she sobs, wearing a new feather boa unfortunately resembling her most recent deceased husband)

His name is Chris CROWE. (Mrs. Walnut Crane-Crowe?)

the mental images of a whole human man learning and performing the crane mating dance, and "sitting" on artificial eggs so she thinks he's performing his duties as a husband and father (and apparently OBJECTS if he does not?)

"chris, buddy, you gotta marry the possibly-murderous crane lady for the GOOD OF THE SPECIES." (alternately: "chris, my man! good news! we found you a very interested lady! She's 36, she's very spirited and independent, she holds a very important and rare status in her society! ...Is there a downside? WELL...")