Ever since I was a child, I’ve always thought the diorama of the Kōtuku or White Heron (Ardea modesta) nesting colony in the Museum's Bird Hall was very cool.
One weekend in early February, I finally got to see the real thing on the West Coast. My sister and I took my parents to it on the occasion of my father’s 80th birthday. It’s even cooler in real life.
The species Ardea modesta is common throughout its greater range of Asia and Oceania, but in Aotearoa New Zealand it is rarely seen. That is because there are only 150–200 Kōtuku in Aotearoa. The population has probably always been this size, even in pre-human times. Our Kōtuku are thought to have originated from birds that flew across the Tasman Sea several hundred years ago. Birds still occasionally fly over from Australia and join the population in Aotearoa.
The rarity of the Kōtuku is captured in the Māori proverb “he Kōtuku rerenga tahi”, which translates as “a White Heron’s flight is seen but once”. This is applied to very rare and special events, as well as visitors of importance.
In Aotearoa, the only place Kōtuku breed is a 30 metre stretch on the side of the Waitangiroto River, just north of Ōkārito Lagoon, Westland. Kōtuku have never been recorded as breeding anywhere else in Aotearoa. Mature breeding birds arrive at the breeding colony in August and display to each other using fine, threadlike feathers they grow for the occasion. Kōtuku form new breeding pairs each season and both the male and female incubate the eggs, which are laid in September–October.
The parents forage in the wetlands around the breeding colony, including the nearby Ōkārito Lagoon. They catch a variety of animals including small fish, frogs, skinks, aquatic arthropods, mice and small birds; however, their primary food during the nesting period is whitebait, which they bring back to the nest and regurgitate for their hungry chicks. The chicks are ready to leave the nest after just over 2 months and the colony is abandoned by early March. When I visited the colony on 8 February, there were just seven birds: a breeding pair with a late-hatched chick and four young birds getting ready to head off. When the Kōtuku leave the colony they disperse all over Aotearoa and forage on their own.
The Kōtuku nesting colony consists of about 30 pairs of Kōtuku every year. It is in dense wetland kahikatea forest and was likely known about by Māori. It has occupied the same space since before it was revealed by the surveyor Gerhard Mueller in 1865. Mueller’s discovery of the site nearly spelled its doom; the breeding feathers were taken to adorn fashionable hats, and nests and eggs were destroyed. By 1941, there were just four nests at the colony. That year, the site was declared a reserve and wildlife refuge to protect it. In 1976 it became the Waitangiroto Nature Reserve. The nesting colony has now recovered and the only public access to the Nature Reserve is through White Heron Sanctuary Tours, which pays a fee to the Department of Conservation, undertakes monitoring and traps predatory pests such as stoats and possums.
For now the colony seems to be stable, however, it may be at the mercy of climate change. More frequent westerly storms and high rainfall in summer can destroy nests and chicks, and flooding of Ōkārito Lagoon can prevent adults from foraging for food. Hopefully the colony can endure and the diorama at Canterbury Museum will continue to provide a taster for those wanting to one day visit the real thing.
