"A new hawk came in and was seen in Pale Male’s nest...the fact that another bird dared come in to the nest means Zena is likely dead," said birder Ann Feldman.
Zena was Pale Male's most recent mate, after Lima, who died after a year with Pale Male, and Lola, who disappeared in 2011 after a nine year romance with him.
Zena's disappearance is adding fervor to a new campaign "Stop the Poison" aimed at getting institutions in red-tailed hawk territory to stop using rat poison.
Campaigners have been calling the American Museum of Natural History, the Central Park Boathouse, the Central Park Police Precinct and the Metropolitan Museum of Art and pleading with them to stop using rodenticide. Only the Met has heeded their requests so far, according to the group.
"The Met said that they removed all poisons after they heard of the hawks being poisoned by them," said organizer JoyAnn Savino.
The American Museum of Natural History, however, which as of August had more than 10 bait boxes scattered around its premises and was the place where one of the poisoned baby hawks was picked up, has been unresponsive, said Savino.
"The AMNH has not returned any calls or emails that we sent them," she said.
The museum did not return multiple requests for comment as to the contents of the bait boxes spread across its premises.
This summer, two of Pale Male's baby hawks suffered from rat poisoning and were taken to Long Island by the group Wildlife in Need of Rescue and Rehabilitation (WINORR). Bobby and Cathy Horvath, the couple behind WINORR, said they will not return the hawks to Central Park until they know rat poison is not being used.
Organizers said the campaign was aimed at educating people that better sanitation is the best recourse in combating a rat invasion, not poisonous bait. It's a policy the Department of Health supports as well and is promoting in a series of "Rat Academies" across the West Side.
"[Institutions] are not going to develop anything safer until their feet are put to the fire," said Feldman, who is also part of the campaign.