Forest & Bird member Catriona Gower has been leading monthly dawn and dusk expeditions of local volunteers since October, in the hope of hearing or spotting the rare and elusive wetland bird in areas around Catlins Lake and Maclennan.
The group’s monitoring — which concluded this past weekend — is feeding into the nationwide "Great Matuku Muster", which aims to assess numbers of the critically endangered species across the country.
The bittern (matuku-hūrepo) has experienced a severe decline in numbers during recent years as its wetland habitat disappears.
Ms Gower said hearing the large and striking bird was more likely than seeing it, as it had good camouflage and could freeze when it detected a threat.
Instead it was known for its characteristic booming call — particularly during spring full moons as males staked out territory and sought mates.
Although the recent weekend had not yielded any trace in the Catlins, monitoring this spring had been "heartening" overall, she said.
"We have electronic detectors in the area, which are picking up calls, and we’ve also had volunteers who’ve heard calls in both October and November, and a sighting in October.
"The collated New Zealand results seem to suggest numbers nationwide are around 750 to 800, which is lower than the upper end of estimates. It’s heartening to know they’re present here in the Catlins, although much more can be done to improve and expand their wetland habitat and their prospects for survival as a species," Ms Gower said.
She said she did not want this to be the last generation to experience the birds’ "magic".
"When present, they’re a very distinctive feature of the quiet early morning soundscape. When you first hear one it’s a case of ‘What was that?!’ The call is very low frequency, so it can travel for a long way across the water and is quite magical."
The wider project aimed to monitor the bird over a five-year period, to inform future management.
Bittern booms have been recorded in the Catlins and Sinclair Wetlands, Lake Tuakitoto and Akatore in Coastal Otago. They have also been sighted in the Maniototo, Central Otago, near Glenorchy and at Coronet Station.
