A rare bird
Rare in New Zealand, with a population of just 100–120 birds, the elegant white heron or kōtuku (Ardea modesta) is nevertheless common in India, Japan, China and Australia, where it is known as the great egret. With a long, slender neck, yellow bill and thin legs, white herons grow to 92 centimetres in length and 900 grams in weight. In flight their long neck is held kinked. During breeding their bill darkens and a veil of fine feathers extends beyond the folded wings and tail, accentuating their graceful profile.
Kōtuku had mythical status for Māori because of their rarity and beauty. The epithet ‘te kōtuku rerenga tahi’ (the white heron of a single flight) was given to distinguished guests who seldom visited.
It is not known exactly when the only heronry in New Zealand – near Ōkārito in south Westland – became established, but it is presumed that a few hundred years ago a favourable wind carried some birds over from Australia. This sometimes still occurs: in the winter of 2013 many trans-Tasman strays appeared throughout the country, forming small flocks of five to seven birds from Otago north to Hawke's Bay.
The Waitangiroto colony
White herons have not spread out to form new breeding colonies elsewhere, although they disperse widely during winter before returning to Waitangiroto (near Ōkārito) to nest. Some birds scatter to northern estuaries; others may occasionally harass goldfish in city gardens, or be driven by winds as far as the Chathams or subantarctic islands (although these birds may come direct from Australia). Otherwise they feed mainly in estuaries on a diet of whitebait, small fish and eels, aquatic insects, shrimps, tadpoles and frogs.
Māori had probably long known about the colony, set in dense forest alongside the sluggish Waitangiroto River. They captured individual kōtuku, but ensured that the total population remained viable. Birds were kept in cages and every few months one of the feathers was plucked for use as an adornment.
The long breeding feathers of kōtuku were considered by Māori to be tapu, and were used to adorn the hair of chiefs and other men of high rank, or their cloaks and kites. Women wore only the shorter plumes. If a man dreamt that he saw the skull of his ancestors decorated with kōtuku feathers, it meant his wife’s baby would be a boy; the black feathers of the huia foretold the birth of a girl.
When European settlers discovered the colony in 1865, vandals destroyed the nests and eggs, and the feathers were taken for fashionable women to wear in their hats. By 1940 there were only four nests left.
First steps to protect the area were taken in 1924, when a 60-metre-wide strip on either side of the Waitangiroto River was declared a sanctuary from logging. In 1941 it was declared a fauna and flora reserve. It was guarded by a resident warden, and access to the ground was controlled during the breeding season. In 1957 the colony was gazetted as a wildlife refuge, and it became the Waitangiroto Nature Reserve in 1976.
Surrounded by swamps and rivers, the colony has some natural protection, although not enough to prevent stoats and harrier hawks preying on chicks and fledglings. To help these young survive, the New Zealand Department of Conservation runs a stoat-trapping programme.
Limited numbers of tourists can visit the colony during the breeding season. The birds are viewed from a hide across the river to avoid disturbing them.
The Waitangiroto colony is unusually long lasting, with only minor movement within the same general area. In the United States the average lifespan of a heron colony is only five years, and in Australia 18 years. There are two main reasons for the colony’s longevity: the number of birds is relatively small, so vegetation is not killed off, and visitors are kept to a minimum and concealed in a hide, so they do not frighten the herons away.
In August and September white herons arrive at the Waitangiroto colony to nest in kāmahi, māhoe and kōwhai trees, and in the crowns of tree ferns. The birds undergo a transformation: their bills turn black and they develop long, white, loose breeding plumes on their backs and wings. Females lay three to five pale blue-green eggs in September or October, and both sexes share incubation. When the chicks hatch, they are fed by both parents until they fledge at around 42 days. They disperse from the colony three weeks later and may live up to 22 years.
Since observation began in 1944, the number of recorded nests reached a high of 65, with 60 fledglings, in 1981. Since 1982 the number of nests has remained at around 40–50.
Climate is key to the survival of chicks. Since 1950 the westerly airflow to New Zealand has increased, causing more storms and greater rainfall in Westland, especially in summer. These have destroyed nests and killed chicks in some years. The Ōkārito Lagoon occasionally floods, preventing adult white herons from fishing for their staples of whitebait, eels or freshwater crayfish, which means they cannot feed their young. This has happened with increased frequency since 1967.