Seeking the elusive "Swamp Boomers" of New Zealand
On a small lake in central Hawke’s Bay, the quest is on to find one of New Zealand’s least understood species before it vanishes forever.
The first boom came as a surprise. As I navigated my kayak through the marshy northern reaches of Lake Whatuma, I could hear the whistling of dried raupō plants, the slap of water against the kayak’s hull, the high, eerie calls of black swans. Then, in a pitch so low I could almost feel it, a boom reverberated from the reeds. It was the throaty call of a male Australasian Bittern Botaurus poiciloptilus.
A few metres from my boat, bittern scientist Dr Emma Williams steered her kayak towards the sound. A sleek black Labrador-cross was in the bow of the boat, tail wagging beneath her fluorescent “Conservation Dogs” coat. “Good girl, Kimi,” says Williams, pushing reeds aside as the pair disappeared into the raupō.
Williams, a wetland bird expert, is at the forefront of Australasian Bittern research in New Zealand. Known as matuku to Māori, these heron-sized birds sport striped plumage that mimics the raupō-filled wetlands in which they live.
Bitterns will “freeze” rather than fly on being discovered, pointing their long, thin beaks skyward and swaying for better camouflage. Spotting a bittern can feel like searching for the proverbial needle in the haystack – if the needle were the colour of straw.
The team of volunteers accompanying Williams' search at Lake Whatuma was prepared for the challenge. We went during the spring mating season, when males of this usually silent species can be heard “booming” from their territories. The sound is created by the bird deeply inhaling and then deflating a bagpipe-like sac near its throat. The resulting booms helped us locate the bitterns’ hideouts.
As well as the bitterns’ calls, we had Kimi. The first conservation dog in Australasia trained to track bitterns, Kimi has a nose for scents raupō couldn’t conceal. She stood at attention and sniffed for birds as Williams pushed their kayak through the reeds. When paddling became impossible, Williams jumped into the thigh-deep water and follow Kimi through the raupō. I paddled out into the lake with one of the other volunteers to keep an eye out for flushed birds. We excitedly called Emma on the radio when a disgruntled male bittern emerged in front of us: “You found one!” we said.
During this trip, Williams was searching male bitterns’ territories to locate females and their nests as part of her doctorate for Massey University. Her goal was to capture and attach a transmitter to a female or chick, which would provide data on these elusive birds and fill in some longstanding research gaps. Unfortunately, while we heard and spotted several male bitterns, we were unsuccessful atfinding females this year.
Bitterns are notoriously difficult to study, and data on the species is limited. What is known is that 90% of bitterns’ wetland habitats have been destroyed and that ongoing habitat loss remains their biggest threat. An estimated 900 Australasian Bitterns remain in New Zealand, with about 1000 living in Australia and 50 in New Caledonia. “Bitterns are ranked as a nationally-critical species in New Zealand,” says Williams. “That’s the same threat level as kākāpō. Kiwi and kōkako are more common.”
Unfortunately, Australasian Bitterns - assessed as Endangered by BirdLife on behalf of the IUCN Red List - receive nowhere near the same amount of attention as their famous counterparts. Williams isn’t sure whether this has more to do with their elusive nature or with the fact they thrive in habitats humans tend to marginalise. Even a national stronghold for the species – the Waikato’s renowned Whangamarino wetland – is routinely flooded and drained for agriculture, drowning territories as well as nests. In the face of such massive fluctuations, Emma grimly expects this population to disappear within a couple of years.
“In 2010, it was common to hear 50 or more bittern calls at Whangamarino within a 15-minute period,” says Williams. “Our biggest problem was that there were too many calls and birds for observers to keep track of! Now we’re lucky if we find seven birds in the entire 7100ha wetland.”
Williams believes that awareness can change attitudes. She continues her work as a consultant with Massey University, Ducks Unlimited, and DOC’s Arawai Kākāriki wetland restoration programme. With the assistance of partners including local Forest & Bird (BirdLife in New Zealand) branches, Williams is increasing what’s known about bitterns in the hopes of giving them a story as compelling as that of kiwi or kākāpō.
“Bitterns appeal to people because, even though they’re so rare, they’re also very accessible,” she says. “You can hear them in the wetlands near your town, and they’re often found on people’s farms”.
Or even closer. Williams is fond of recounting the story of a juvenile bittern that wandered into a suburban Christchurch garage. The very confused homeowner brought the bird to local bird rehabilitator Jackie Stevenson. “I think I’ve got a kiwi,” the owner said. “No,” said Stevenson, “you have something even better.”
Bitterns are a potential indicator of wetland health because they depend on the presence of high quality and ecologically diverse habitats and rich food supplies. When Europeans arrived, they were abundant, but now it is rare to see more than one at a time. Bitterns are also found in Australia and New Caledonia, but populations there have declined dramatically and they are now classed globally as endangered.
In New Zealand, they are mainly found in wetlands of Northland, Waikato, the East Coast of the North Island, and the West Coast of the South Island. They feed, mostly at night, on fish, eels, frogs, freshwater crayfish, and aquatic insects. Matuku are important to Māori. They appear in language as part of legends, stories, early pictures, and metaphor, and there are numerous place names referring to them. They were important for food, and their feathers were used for ceremonial decoration.