An injured bittern taken to Rotorua's Wingspan could provide information about the shy and endangered species.
Wingspan director Debbie Stewart said she was compelled to help the swamp bird, even though it was not a bird of prey, when Rotorua man Joe Fleet brought the bittern to Wingspan last Friday.
There are fewer than 1000 bitterns surviving nationally.
"The man was fishing near Atiamuri when he came across the bird. The fact that he was able to spot it and capture the bird meant that it was quite unwell.
"It's not normal for us to accept sick and injured birds that are not birds of prey, but given the conservation interest we had to make a special case."
Ms Stewart said there was nothing visibly wrong with the endangered bird which is now being sent to Massey University in Palmerston North for an X-ray and blood tests.
"There was no blood, there were no scratches and it was holding its wings normally and had not lost breast muscle, which shows it had not lost its condition. It might have been stunned by a car or ingested something."
Massey University PhD student Emma Williams plans to use a transmitter to study the movements of the bird, which she believes to be a female, once it is released back to where it was found.
"The bittern is rarer than the brown kiwi and kokako, but we know so much more about those other species than we do the bittern. The bittern is very shy and doesn't like people. Ninety per cent of its natural habitat has gone. It will be the first female bittern to have a transmitter attached to it."
The bird is expected to be released over the next two weeks.