New Zealand’s most secretive wetland bird is about to start booming, and a volunteer-run project wants 1,200 people sitting quietly at the edge of swamps, lakes and reed beds to count it.
The Great Matuku-hūrepo Muster, a national count of the Australasian bittern that takes its name from the bird’s Māori name, opens its first listening window this Friday, 18 September. Love Bittern Project founder Wendy Ambury told RNZ’s Checkpoint on Tuesday that the count usually draws 400 to 500 volunteers a year, and she is hoping for at least 1,200 this spring.
The timing matters in another way too. The bittern is standing in Forest & Bird’s Bird of the Year competition for the Shy Birds party, where its status is listed as “In serious trouble”. Voting, which opened on 4 September, closes at 5pm on Sunday 20 September, and the winner is announced the following day.
The Department of Conservation classifies the bittern as Nationally Critical, the most at-risk category in New Zealand’s threat classification system. Nobody knows exactly how many are left. The project’s muster page estimates somewhere between 600 and 1,000 birds and describes the species as on the brink of extinction. DOC notes that bitterns were abundant when Europeans arrived, but that it is now rare to see more than one at a time. The species also lives in Australia and New Caledonia, where numbers have fallen so sharply that it is classed globally as endangered.
That uncertainty is the whole reason for the count. Bitterns spend their lives hidden among reeds and rushes, and they move between wetlands, so one bird could be counted at one site on Friday and at another on Saturday. In spring, though, males tend to stay put on a territory and give themselves away with a deep, foghorn-like boom that warns off other males and attracts females. Synchronising the counts across the country is how the project avoids counting the same bird twice.
“Their mighty boom at this time of the year, especially going into spring, their breeding season, is heard across those wetlands up to 5 kilometres away,” Ambury told RNZ.
Because each volunteer notes when a boom starts, roughly how far away it is and which direction it comes from, readings from neighbouring listeners can be combined to pin down individual birds.
“We can actually record the direction that boom is coming from and estimate the distance to the boom as well, which means that we can triangulate the position of each booming and determine how many individuals we’ve got,” she said.
Taking part costs nothing and needs no special gear. According to the project’s 2026 sign-up post, volunteers pick a wetland with deep, stable water and plenty of reeds or rushes, then listen for 60 to 90 minutes before sunrise or after sunset on one to three consecutive days. For each sequence of booms they record where they are listening from, the time it started, how many booms it contained, the rough distance (near, medium or far is fine) and the bearing. Results can go on a paper field sheet or into The Conservation Hub app.
There are three windows this year, from Friday 18 to Sunday 27 September, from Friday 23 October to Sunday 1 November, and from Friday 20 to Sunday 29 November. The project asks North Island listeners to aim for the weekend closest to the full moon in September and October, and South Island listeners to do the same in October and November. It recommends 90-minute sessions in Otago and Southland because twilight lasts longer there. Anyone unsure of their local sunset time can look it up in Newswire’s daylight hours tool.
The flexible dates are new. The muster page is candid that “Last year’s results were marred by the weather”, so this year groups can choose their own three consecutive nights within each window and set backup dates as well.
Casual sightings are rising too, although that probably says more about people than birds. A Newswire count of verifiable bittern records on the citizen-science platform iNaturalist found about 10 a year in New Zealand between 2014 and 2017, rising to 57 in 2022 and 92 in 2025. The same records show how much easier the birds are to find in the breeding season. Each month from September to December has between 48 and 55 records, while every other month has between 19 and 37. The Love Bittern Project’s own tally for the year to 30 June 2026 reached more than 2,200 observations, including more than 1,500 logged through the project and 550 on eBird.
Behind the numbers is a habitat story. DOC’s wetland restoration programme says wetlands once covered 2.4 million hectares of New Zealand, but more than 90 percent have been drained or cleared. Bitterns need high-quality wetlands with rich food supplies. They feed mainly on fish, including eels, and also take freshwater crayfish, frogs and insects, according to New Zealand Birds Online. The same reference, last updated in 2022, notes that Whangamarino Wetland in Waikato was thought to have as many as 145 bitterns in the 1980s, while more recent reports suggested fewer than 15 males were attempting to breed there.
“As long as we continue to lose wetlands, we’re losing that vital habitat that they need to thrive,” Ambury said.
DOC is working on the counting problem from its side as well. Its bittern page says the department has been developing call counts, with observers listening at dawn or dusk or with automatic recorders built by the DOC Electronics Lab, and that it published a manual in 2024 on the species’ habitat needs, threats and management. DOC researchers also fit some birds with GPS trackers, which Ambury told RNZ gives vital information about how the birds travel from region to region.
DOC says bitterns are mainly found in the wetlands of Northland, Waikato, the East Coast of the North Island, the West Coast of the South Island and Southland. For most people the contribution is simple. RNZ reported the task involves finding your nearest wetland, sitting at the edge of it and keeping an ear out for booming. The sign-up form, a how-to guide and the community workbook are all on the Love Bittern Project website.
Have you ever heard a bittern boom, or will you be out listening this spring? Tell us where in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
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