One of the Rotorua Museum karearea has been euthanised, six weeks after being injured.
The urban release in December was a New Zealand first, and Wingspan director Debbie Stewart said despite the sadness surrounding Te Rangi Rere I Waho, known affectionately as Maureen, they were looking at a further release this summer.
Maureen was euthanised on Thursday. In July, she was found to have a significant abrasion on one of her legs and a smaller abrasion on one of her wings. She had a toe amputated a couple of weeks later and was expected to recover fully.
Ms Stewart said the Wingspan team was "gutted" by her death.
"After a successful summer and the community engagement this isn't something we were expecting, but we tried our best," she said.
"The foot injury compromised her other leg due to the extra weight and she deteriorated. We wanted her to pull through but we couldn't save her. It's hit us all hard.
"It's not often we can't pull birds through, particularly when it's a bird that's special to the community."
Three falcon chicks were released last December. The other birds are Hatupatu and Tametekapua. Hatupatu remains at the Government Gardens, while Tametekapua has been sighted courting a female falcon at the Arikikapakapa golf course.
"We're really encouraged by that. People have been reporting sightings quite regularly, we've never had so many sent in - people are taking pride in them and that's quite warming for conservation.
"The first release was essentially a trial to find people's tolerance. We still consider it to be a success and we have plans to have another release of birds in the summer months."
Ms Stewart said they did not know what caused Maureen's injuries but they had not ruled out deliberate harm.
"We have received reports from members of the public concerning the welfare of the falcons, but this isn't a witch-hunt, instead we prefer to celebrate how special Te Rangi Rere I Waho has been as an advocate for her species."
The On the Wing project in partnership with the Rotorua Museum has had an estimated reach of more than 800,000 people.