There's a native bird so secretive you aren’t likely to see it but you could be lucky enough to hear its 'boom' call, resonating across the wetlands. Kinsa Hays went to 'hunt the boom'.
Unlike the cheeky kea or distinctive yellow-eyed hoiho, the matuku, or Australasian bittern, flies under the radar. There are fewer than a thousand left dotted around the country, its population at critical levels as its wetland habitat disappears.
Matuku used to be abundant throughout Aotearoa and they've been described in Māori legends and stories. But now they are critically endangered, mainly because the wetlands they depend on for nesting and food have gradually been cleared over the last century to create farmland.
The bird is knee-high, with light and dark brown-streaked feathers camouflaging it amongst the bulrush. If disturbed, they freeze in a pose with their beaks stretched high and even sway with the reeds. Blink and you'll miss them. They live around the edges of lakes, salt marshes, creeks, paddocks, culverts, and drains on farms; their resonating 'boom' bird call once common to hear.
I had a chance to play a new game, 'Hunt the Boom', along with a small army of Department of Conservation (DoC) volunteers in Tauranga last year, carrying out a ‘call count’ to find out how the birds are faring in the Bay of Plenty.
In pairs, we sat around Maketu's salt marshes at dusk for a couple of hours. Over three evenings in a row we observed everything, listening for booms and recording the results – I heard just one boom. In total, we heard a mere thirty booms; we heard dogs barking more often.
Karl McCarthy, a Tauranga DoC biodiversity ranger, is passionate about matuku, even spending his weekends knee-deep in swamps around the Bay of Plenty, trying to catch a glimpse.
“Bitterns are cool. I became interested in them when half-starved bittern chicks were handed in from estuary suburbs around the city. They would have just left the nest and probably couldn’t find enough food in their diminishing environment. The reduced water quality for their prey – fish and eels – doesn’t help either.”
Since the mid 1800s, 90 percent of New Zealand's wetlands have been lost, drained to create farmland. They are valuable ecosystems that act like the kidneys of the earth, cleaning the water that flows into them, and they support the greatest concentration of wildlife out of any other habitat. The few wetlands that do remain are degrading because of things like run-off pollution, stock grazing, pests and invasive plants, which kill the bittern's food sources.
Some of the birds that have been tracked by researchers have starved to death trying to find food. Two juvenile matuku from Travis Wetland in Christchurch were found starving and kept until healthy, then released. But over winter, one travelled south to look for food in wetlands and eventually died of starvation near Temuka.
McCarthy says little is known about the species as they are ‘cryptic’ - hard to see and study because of their elusive nature and camouflage tactics. Because of this, and the disappearance of its habitat and subsequent decline in population, it’s really only in recent years that there have been concerted efforts to learn more about them.
DoC science advisor Emma Williams has discovered a lot about the birds. While doing her PhD in ecology at Massey University she developed a sneaky method to catch them: she played recordings of male booms to lure birds into a trap with a mirror on it, in an area where the birds have been spotted before. A curious male matuku investigated, attracted by the sound and his own reflection. Since then, she has caught several more, often naming them after 50s crooners like Elvis Presley, Prince Tui Teka and Bing Crosby. Catching a female bird is still a work in progress as they don’t seem respond to this method.
After attaching tiny transmitters to the male birds, Williams learned that they flew much further afield than was thought – some over 300km. This also means that when call counts are carried out, it’s likely the same bird being counted twice, distorting population estimates.
Seeing matuku perform a boom is even rarer than hearing it: the male jumps up and down to make a bowl-like platform for his coming performance. When he’s satisfied, he hunkers down and crouches, turns himself into the equivalent of a bagpipe: his long neck becomes the pipe and his body like the bag held under the arm. He takes an inward breath, then he squeezes the compressed air through his oesophagus in a rush which creates a deep and resonant sound, in a sequence of three to five. He’s trying to attract a female and beat competitors with the quality of his boom; a loud carrying boom is needed to cover the distance of a wetland. If a competitor does three booms, the next guy has to do more or boom more often.
There is currently no recovery plan for matuku, but DoC is focusing on developing methods for surveying the birds systematically and for restoring wetlands. There is hope – last year, matuku were spotted for the first time amongst newly restored wetland plants at Whangamarino in Waikato.
The public can also help create refuge for the bird: property owners can fence and protect wetlands; volunteer with the NZ Wetlands Trust; attend a restoration planting; and leave dogs at home when visiting wetlands.