Australasian bittern / Matuku-hūrepo
- Apr 30
- 3 min read
Whangamatā Harbour Birds
This protected, critically endangered species is present in very small numbers and seen only very occasionally in the freshwater wetlands adjoining the Whangamatā Harbour and the Otahu Estuary. They also occur in small numbers on the nearby Wharekawa Harbour wetlands, to the north of Whangamatā. Because of their cryptic plumage, secretive nature and habitat of feeding mainly at night, their presence often goes undetected.
As well as being widely distributed throughout wetlands in New Zealand, this bittern species occurs naturally in parts of southern Australia and New Caledonia. They favour freshwater and estuarine habitats surrounded by dense beds of raupo, tall rushes, reeds and rank grasses. Because of their secretive nature, accurate estimates of populations at all these sites is difficult to assess, but there is sufficient data to suggest they are in danger of becoming extinct in the near future unless greater conservation resources and efforts are extended. Fewer than 800 birds are thought to remain in New Zealand. Whangamarino Wetland in the Waikato was thought to support 145 bittern in the 1980’s but recent reports suggest less that 15 males breed at that site now. Similar levels of decline are reported in Australia with less than 1000 birds remaining, and in New Caledonia currently having fewer than 50. In NZ their decline has been largely attributed to the drainage and fragmentation of their wetland habitats, deteriorating water quality leading to reduced feeding opportunities and predation by introduced predators.
The bittern is a member of the heron family, a large stocky bird with a thick neck, longish yellow legs and variably patterned mottled brown and buff plumage. It is sometimes mistaken for the more common harrier hawk. The males weigh around 1.5kg and the much smaller female 1kg. When flushed (takes flight from its hiding spot), they rise in a labouring flight powered by their broad rounded wings. Once obtaining sufficient height and speed they fly with a slow steady wingbeat, head withdrawn and legs trailing well behind their tail feathers. Bitterns' food hunting strategy is to either remain motionless and wait at favoured feeding spots for their prey to come to them or by slowly stalking the shallow wetland fringes until close enough to take their prey quietly without having to take rapid lunges like, so many other wading bird species do. Their diet consists mainly of eels and small fish, but also spiders, insects, snails, worms, crabs, frogs and lizards.
Because of their secretiveness, sensitivity to disturbance, nocturnal habits and the dense nature of their habitats, bitterns breeding, feeding and socialising habits are not well understood. Very few bittern nests have been found and studied. The nest is usually constructed of reeds and tall grasses in a platform well hidden amongst the available dense wetland vegetation and close to areas of open water including freshwater lakes, ponds, streams and drainage ditches. Between 3-5 eggs are laid and incubated for about 25 days before hatching. The nestlings remain in the nest for about 7 weeks. The female bittern undertakes all the incubating, brooding, caring and feeding duties during which time they and their chicks are extremely vulnerable to introduced predators (wild cats, mustelids, rats and hedgehogs) and to any flooding events that happen. Re-nesting is unlikely to occur in such circumstances due to the weakened condition of the female following her first attempt.
Because of their secretive and solitary nature, their preference for living and feeding amongst or close to dense areas of tall wetland vegetation, and their extremely low numbers, it is most unlikely many people will ever have the opportunity of seeing one of these birds. When disturbed they often slink away unseen into the nearby cover or simply ‘freeze’ with their neck head and bill stretched upwards, using their suitably camouflaged plumage to blend them in perfectly with the wetland vegetation.
Some people may be lucky enough to hear a male bird making its territorial “booming” calls during the species breeding season (August to December). The most likely spots to do this in the Whangamatā area are wetlands at the southern end of the Moana Anu Anu Estuary and wetlands adjacent to the Waiharakeke Stream in the upper Otahu Estuary.
— John Adams, Whangamatā Harbour Care
Photo Credits: Imogen Warren
