Safe and sound from predators, some of Orokonui Ecosanctuary's population of robins have surprised researchers by nesting on the ground.
This season, eight of the 10 breeding pairs which remain inside the ecosanctuary, successfully produced 32 fledglings.
University of Otago associate professor Ian Jamieson said the level of breeding was higher than expected when the birds were initially relocated from the Silver Peaks.
Pairs had two or three clutches each.
Eight of the pairs were birds released last year and the other two were from the first release.
Another surprise was that two pairs built their nests directly on the ground and one pair had done so for three consecutive clutches, he said.
"In my 12 years in studying robins on the mainland and on Ulva Island [which has predatory weka], I have never seen a robin build a nest directly on the ground."
The nests were well concealed with overhanging branches or ferns, a practice also known among bellbirds and saddlebacks on some offshore islands.
In addition to a lack of predators, the breeding success could be put down to the right vegetation and invertebrates, he said.
While the fledglings did not have transmitters on them, they could be seen on either side of the track in the bottom end of the ecosanctuary and appeared to be settling close to their parents.
"This means the breeding population could double next year."
The survival rate of nests was also high in the Silver Peaks, following an Animal Health Board 1080 poisoning operation to kill possums.
"But the Orokonui robins are doing very good, relative to the others."
Monitoring of the Silver Peaks population showed the relocation of birds had not had an impact.
