An adult matuku or Australasian bittern is so good at being undercover, that it is often difficult to find and track. Photo / Imogen Warren
An adult matuku or Australasian bittern is so good at being undercover, that it is often difficult to find and track. Photo / Imogen Warren
Department of Conservation rangers are trying to track one of Lake Taupō's rarest birds, but it isn’t easy, Milly Fullick reports.
As darkness falls on an October evening, the distinct and repeated sound of booming begins to ring across the wetlands around the southern and western edges of Lake Taupō.
The noises aren’t from overeager hunters, or a mishap at the Tokaanu Power Station.
The booms are coming from birds, and they’re exactly what waiting Department of Conservation rangers are hoping to hear.
The Australasian bittern, or matuku-hūrepo, is a rare and critically threatened bird found in wetlands in New Zealand.
There are thought to be fewer than 1000 of the large, long-necked birds here, but they’re so elusive even the experts aren’t sure of exact numbers.
Department of Conservation biodiversity ranger Karen Ardin uses nothing more than a clipboard, a compass and her senses to monitor bitterns.
That’s where the DoC rangers come in.
Armed with nothing more technical than a compass and a clipboard, staff and volunteers across five sites spent three evenings sitting in silence, hoping to hear the low, unique call males make to attract a mate.
This only happens over a couple of months of the year, during the bittern breeding season, which is usually in October and November.
Over an hour, the rangers note the number of individuals they can hear, noting their approximate locations, as well as the number and frequency of calls.
Bitterns are rarely spotted, but this one (circled) made a brief appearance on a monitoring evening last month.
The birds are expertly camouflaged against the raupō and reeds in the wetlands, so spotting one is even rarer than hearing them.
The monitoring can be challenging for the rangers, especially due to the low-tech approach, meaning that traffic noise, poor weather and even the calls of other birds like geese can make monitoring challenging.
Information from these monitoring sessions is added to recordings from a handful of microphone devices around the area in the hopes of giving scientists a clue as to the bittern population, and whether their numbers are changing over time.
One of the rangers listening out is Karen ‘Ardy’ Ardin, who said people are often surprised to learn there are bitterns living around the lake - not least because most don’t know what they are.
“Most people have never heard of bitterns, even the ones living along the lake.”
Australasian bitterns / matuku-hūrepo live in wetland habitats like the ones found around Lake Taupō.
The birds don’t have the national profile of icons like the kiwi, meaning getting public attention and funding for research can be challenging.
Rangers are determined to do the best they can with the resources they have, said Ardin.
However, the current monitoring research has limitations, as it only tells researchers how many males are in an area calling for a mate, not how many successfully find one, or how many offspring might be produced.
However, it’s the best and most accessible tool currently available, and could help give researchers a fighting chance at understanding more about the birds, and what can be done to help them, said Harry Caley, DoC science adviser on wetland birds.
“This monitoring is general data gathering, as well as contributing to a national programme to assess male activity and presence over time.
“From year to year, we can observe the activity of males competing for territory in these wetlands, and this method can indicate the total number of booming males from site to site during survey nights.”
Gaining an understanding of where the birds are, and in what numbers, gives researchers a starting point in helping protect them, said Caley.
For now, the initial results of this year’s monitoring suggest the population continues to remain relatively steady, with numbers of calls heard similar since monitoring started in 2019.
However, it’s not all good news, as since the monitoring programme started, a bittern was killed by a car in the Waihī wetland area.
