A new way to search for the elusive matuku/bittern, and what it tells us about the Threatened – Nationally Critical bird and its conservation.
By Carisse Enderwick and Lizzie Sharp
We’ve all heard the old saying: if you want to hide a treasure, put it in plain sight and then no one will see it.
Matuku/Australasian bittern have been classified as a species on the brink of extinction and efforts to protect and enhance the birds’ populations have ramped up across Aotearoa. They are a cryptic and highly mobile species, a taonga which excels at hiding in plain sight and moving great distances.
The birds are an enigma among the rushes and grasses. The males, a paradox, with a mating call that booms kilometres across the landscape. “Hear me, but don’t see me,” they declare.
It makes working with the birds interesting and dynamic, but also poses some serious difficulties in trying to protect Aotearoa’s remaining wetlands.
DOC’s Waikato District Office Biodiversity Ranger, Lizzie Sharp, has been working on a project to find out more about these elusive birds.
“In the Waikato we’ve been monitoring the males’ booms every breeding season for the last five or so years,” says Lizzie. “This long-term data tracks trends and unfortunately it shows a steady downward slope for the species.”
The birds’ cryptic nature meant the project team, which includes Science Advisor Harry Caley, needed new methods to gather data about the females, who otherwise remain silent in the wetland. In 2022 Waikato District Office started trialling a thermal imagery drone to detect females on their nests.
“This will allow us to get a greater overview of the species, monitor nest survival or failure, all while not disturbing the birds or the delicate wetland habitat,” says Lizzie.
The thermal drone works best at dawn when the heat signatures of the birds are much warmer than the surrounding vegetation.
“Wetlands are truly beautiful at 5am with the birds just waking up,” says Lizzie. “We fly over areas with preferred matuku habitat. The drone can cover roughly 60ha in a morning and we usually fly it at 60m, scanning for hot spots.”
If there are courting behaviours displayed by the birds, the team comes back in three weeks with hopes of finding a nest. Only female matuku look after the nests, which usually hold four eggs.
“Our aim is to develop a national protocol for nest monitoring which is a more in-depth way of measuring population health. We know very little about females so it also allows us to locate them and GPS tag them to determine where they fly to during the year,” says Lizzie.
“Once we locate a nest, we can put a camera up to observe nest behaviour, survival and threats. We are learning about the biggest threats to matuku nests so we can try to mitigate these to give the chicks an improved chance of survival from predators.”
Whangamarino was historically a stronghold for matuku and, at times, the discovery of no nests has been heartbreaking for the team. Threats to chicks include stoats, weasels, ferrets, and cats, and the drone has revealed some interesting findings – harriers have been seen to prey upon nests.
“We have had two nests each with four eggs and within a couple of days after hatching all of the eggs had been consumed by harriers,” says Lizzie.
“This year has also been extremely wet in the Waikato with multiple flood events. The breeding habitat has been quite different from other years and the booming went on much longer than usual. At Whangamarino we saw a couple of birds showing courting behaviours and had hoped to come back to a nest but unfortunately, we think flooding may have been an issue here.”
Like most projects, there are ups and downs. The downs can be really hard, which makes the ups a welcome relief. Lizzie reflects on some of the lighter moments.
“I have been working with matuku for almost four years now and I am still so hyped when I hear a bittern booming, let alone see one – usually flying off.
“Once I was taking a couple of people on an introductory tour of Whangamarino, and a bittern took off right beside us. I was so excited all I could do was shout – whisper: Bittern! Bittern!
“The two people looked back at me, asking what had bitten me and if I was alright! By the time I recovered from my laughter, the bird was long gone.”
Whatever or whomever may be hiding in plain sight, one thing is abundantly clear: hope.
For every breeding season, for every early morning sunrise, for every hot spot, every bird, every nest, every egg – there is hope.
“I hope matuku get recognition across NZ and Australia,” says Lizzie.
“I hope we can repair the wetlands so there is ample breeding and feeding habitat so matuku can thrive. I hope Aotearoa realises the wonder, importance, significance of our wetlands and that we all come together to protect this dynamic species and its strange habitat.”
There simply cannot be anything less for this bird and its habitat.
To learn more about this fascinating, elusive species, check out this episode of the DOC Sounds of Science Podcast, available wherever you get your podcasts.
Episode #5: We love bittern! – DOC Sounds of Science Podcast
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