Still, successfully staving off the local extinction of the species from New Zealand’s mainland is far from guaranteed.
Research published last month in Australian journal Emu — Austral Ornithology analyses efforts at the Moeraki Peninsula, in North Otago, that have led to a seven-fold increase in the number of nests there over the past 40 years.
Lead author and Dunedin researcher Dr Chris Lalas used that success to conclude that rehabilitation was an effective management technique for the endangered species.
"This [research] is providing the background information to say ‘the system works’," Dr Lalas said.
Yellow-eyed penguin nest numbers at Moeraki have increased at a long-term average of 5% a year since work began there in 1982.
Led initially by the late Janice Jones and her husband Bob, and latterly by Rosalie Goldsworthy and her team of volunteers, the proportion of nests rose from six nests of about 453 nests in the southeast South Island in total, to 43 of about 166 nests in total in 2021.
"This long-term trend of increase has been interrupted by periods of decrease, including the recent decrease that may signal a permanent end to increases," Dr Lalas said.
"Success is not guaranteed.
"We are particularly apprehensive when facing an increasing prevalence of endemic diseases and the appearance of novel diseases.
"Also, we emphasise that the successful rehabilitation of compromised penguins is a highly skilled task that cannot be condensed into following a sequence of bullet points."
Modelling published in 2017 predicted the seabirds’ disappearance from the South Island by 2043.
Four management plans for the species, dating back to 1989, had been developed and implemented in an attempt to mitigate threats to the species, he said.
The first three plans disregarded rehabilitation.
The second plan referred to "penguin ranching" in an appendix.
The third plan said rehabilitation was useful in so far as treatment and rehabilitation of injured birds was "recognised as a means of sustaining public interest and support".
However, in the present plan, implemented in 2020, rehabilitation of the birds was recognised as essential to saving the South Island population.
Since 1986, Penguin Rescue’s work in Moeraki has included rehabilitation of all juvenile or adult birds that conservationists encounter locally with life-threatening injuries, emaciation or sickness.
At the time of writing, 590 birds had been treated and released from the group’s rehabilitation facility.
"We accounted for the effect of rehabilitation on nest numbers by subtracting the number of rehabilitated female breeders and their female descendants from the total number of female breeders.
"Without rehabilitation, nest numbers at Moeraki in 2021 probably would have remained similar to the initial six nests in 1982 instead of the seven-fold increase through four decades," Dr Lalas said.
