By Annie Hill
The original article in Russell Lights | Ngā Mārama o Kororāreka, September 2025 edition
I couldn’t resist it, but in fact it’s not inappropriate: bitterns freeze when approached, are masters of camouflage, and have put a lot of effort into being undetectable. They are cryptic (which, in wildlife terms, means having the ability to avoid observation or detection by other animals) and secretive, and their plumage blends inconspicuously into the background—ideally a reed bed—difficult terrain for human beings. When disturbed, they prefer to freeze, beak pointing vertically, or drop down flat on the ground and rarely choose to fly away. Their secrecy means that we know surprisingly little about them and, indeed, if it were not for the distinctive booming call of the males during the breeding season, we’d probably be largely unaware of their existence.
Most New Zealanders are unaware of them, but that can also be explained by their rarity. Four varieties of large botaurus, once considered to form a single genus, divided into sub-species, are found scattered around the Americas, Europe, Africa, Asia and Australasia, and are very similar in appearance and behaviour. While generally considered to be of “Least Concern”, due to their wide distribution, in too many places they are locally extinct or critically threatened.
New Zealand once had its own little bittern (Botaurus novaezelandiae), butthatwent extinct about 1890. Like their cousins, they preferred to live in wetlands. The matuku-hūrepo (lit. heron bittern)/Australasian bittern is native to Aotearoa and used to be widespread, but the draining of 90% of our wetlands has driven them to the edge of extinction, both here and in Australia.
Ongoing habitat loss is one of their greatest threats, although predators, poor water quality, and declining food sources all contribute to their woes. Recent radio-tracking studies have suggested that winter starvation may be contributing to population declines. Nest success and chick/female survival are also probably very low: they’re rarer than both whio and hoihoi. Australia and Aotearoa each probably have fewer than 1,000 adult birds, with about 50 in New Caledonia, but it could easily be half of that.
The fact that they’re hard to see, that the males only ‘boom’ in the breeding season, and that they fly long distances, make it very difficult to be sure. The IUCN classes them as ‘vulnerable’, and DOC as ‘threatened – nationally critical’. Russell Landcare Trust has teamed up with the Love Bittern Project to organise a series of co-ordinated volunteer events dedicated to listening for bitterns at selected locations during the spring. See:
www.russelllandcare.org.nz/event/the-great-matuku-hurepo-muster-2025-round-1
Bitterns, being part of the heron family, fly with legs trailing and neck curved into an S-shape. They’re large, stocky birds, about 75 cm long, with a wingspan around a metre; the 1,400g male is significantly larger than the 900g females. Hūrepo have streaky dark-brown and beige plumage, which varies from bird to bird and probably according to age, although no-one is quite sure.
They’re remarkable birds, but undoubtedly the most remarkable thing about them is how the male calls in the breeding season. They make a unique sound, known as a ‘boom’, in sequences of 1–10, but generally about 3. Possibly the longer sequences imply a fitter bird because the booming seems to take a lot of effort. Females are generally silent, apart from when they return to the nest or if they’re alarmed.
The female builds a platform of reeds, hidden in wetland vegetation, 20–30 cm above the water, although few nests have been found or studied. She lays 3 to 5 eggs between August and December (peaking in November), and incubates them alone for about 25 days, leaving the nest to feed and then regurgitating for the chicks. Meanwhile, the male patrols their territory, booming to keep others away.
Chicks stay in the nest for about 7 weeks and fledge from November to May. We’ve no idea how long they depend on their mother, at what age they first breed, or how long they can expect to live. Occasionally bitterns are encountered in pairs, but they’re generally solitary. While normally polygamous, males outnumber females here, so this may be uncommon behaviour.
Hūrepo are generally found in wetlands across Waikato, Northland, the East Coast of the North Island, and the West Coast of the South Island, but in summer can often be found hunting round drains or flooded pasture. In other countries, bitterns live among reeds, while ours are found in a wider variety of habitats, including coastal estuaries, particularly in winter, probably because of lack of both preferred habitat and food.
They eat a wide variety of small animals, from invertebrates, fish and eels to lizards and mice. However, their prey of choice is small fish, so the clarity of water is vitally important, because they generally stalk them in shallow water. The degradation of water across the motu, plus the management of wetlands by sluices, etc, conspire to make hunting more difficult. A thriving bittern colony is an excellent indicator of a healthy wetland.
While often nocturnal and most likely to be observed at dawn or dusk, they sometimes feed during the day and have even been observed on roadsides, including in Russell.
Hūrepo/bittern deserve to be better known and protected, and could undoubtedly be helped by citizen science. Join in the Great Matuku-Hūrepo Muster and see if you can hear one.
Australasian bittern | Matuku-hūrepo. Adult walking through pasture. Eastern Southland, August 2015. Image © Glenda Rees by Glenda Rees.
(https://www.flickr.com/photos/nzsamphotofanatic/ https://www.facebook.com/NZBANP)
