Kākāpō Recovery Group posted a message on its social media this week the kākāpō population has dropped to 244 after the deaths of Ranger, Madeline and Ōtepoti.
Department of Conservation kākāpō operations manager Deidre Vercoe said yesterday the deaths were unrelated.
She said at the start of the month, 5-year-old Ranger was found on Pukenui/Anchor Island in a fallen tree, seemingly killed in a large windfall.
Then last week, two more of the species died.
Two-year-old Madeline was euthanised after being found in the wild with a severe beak injury.
"She received treatment for several months, but with the support of international avian vets it was determined the damage to her beak was permanent and beyond repair."
He did well at the sanctuary until he breached the fence twice so, after taking part in a climbing trial, he was returned to the southern islands in June.
However, recently, he was found to be underweight and unwell at his scheduled health check and was transferred to Dunedin Wildlife Hospital for care, she said.
"Despite appearing stable, he died shortly after, and his cause of death is currently unknown."
Ms Vercoe said with less than 250 birds, the kākāpō population was critically endangered.
"While a level of mortality is to be expected in any population, the recent loss of three birds over the last month is a reminder of their vulnerability."
The next kākāpō breeding season was predicted to be in 2026 and the Department of Conservation hoped to support the growth of the population.
"Until then we will continue to monitor the population with remote technologies and via annual health checks."
