White heron

Ardea modesta J.E. Gray, 1831

Order: Ciconiiformes

Family: Ardeidae

New Zealand status: Native

Conservation status: Nationally Critical

Other names: great egret, great white heron, kōtuku, kotuku, great white egret, eastern great egret

Geographical variation: Sometimes considered a subspecies of the great egret Ardea alba

White heron. Adult in breeding plumage. Wanganui, July 2007. Image © Ormond Torr by Ormond Torr

White heron. Adult in breeding plumage. Wanganui, July 2007. Image © Ormond Torr by Ormond Torr

The white heron or kotuku is well-loved by the New Zealand people, but it is rarely seen except by those who specifically seek it out. Its sole New Zealand breeding site near Okarito Lagoon in Westland is well-known and well-protected, but elsewhere it is 'He kotuku rerenga tahi' or the bird of single flight, implying something seen perhaps once in a lifetime. When seen in close proximity it is a magnificent bird, with its large size and clean white plumage.

Identification

A large white heron with a long yellow bill, long dark legs and a very long neck. When breeding, the bill becomes grey-black and long filamentous plumes develop, mainly on the back. In flight, the white heron tucks its heads back into its shoulders so that the length of its neck is hidden, giving it a hunched appearance. When walking, the white heron has an elegant upright stance showing the extreme length of its neck. When resting it is more hunched with its head tucked in, making the birds appear more bulky. Important identification characters when separating white herons from other white egret species in New Zealand include overall size, relative neck length, bill colour and shape, and how far the gape (i.e. the corner of the mouth) extends back in relation to the eye. The white heron is the largest, longest-necked of the egrets, and the gape extends well behind the eye.

Voice: a harsh croak.

Similar species: the most similar species in New Zealand is the plumed egret, a vagrant species which is smaller (the size of a white-faced heron), with a shorter neck, never has a dark bill (cf. breeding white heron), and the gape extends to level with the eye, but not beyond. Plumed egrets show a strong preference for freshwater wetlands, and so rarely occur in estuaries, whereas white herons are equally at home in both freshwater and brackish habitats.

The royal spoonbill is nearly as large as the white heron but, as its name suggests, it has a very large spoon-shaped (black) bill. This makes it easy to distinguish between the two species. Non-breeding cattle egrets have similar colouration but are a third the size of a white heron, with a much shorter neck. Cattle egrets are often seen as flocks in pasture, but beware of lone birds in estuarine habitat or wetland. The little egret is much smaller, with a rapier-thin black bill.

Distribution and habitat

White herons are most often seen in harbours and estuaries, but they also visit freshwater wetlands, including high country lakes, and are vagrant to several outlying island groups (Chatham, Snares, Auckland, Campbell and Macquarie Islands). The only New Zealand breeding colony is on the Waitangiroto River, just north of Okarito Lagoon, Westland. About 30 pairs of white herons breed here, mainly in the crowns of tree ferns over-hanging the river, under tall kahikatea forest. A viewing hide at the site can be visited during the breeding season via a jet-boat ride and a short walk, with access managed by an ecotourism operator licensed by the Department of Conservation.

Population

White herons are widespread and abundant throughout Asia and Australia, where they are generally known as eastern great egrets. The New Zealand population is small (150-200 birds) but apparently stable.

Threats and conservation        

The Okarito heronry has occupied essentially the same site since before its location was revealed by a surveyor in 1865. White herons have never been recorded attempting to breed anywhere else in New Zealand. Despite the risks of the entire population breeding at a single location, the colony has thrived throughout. It is well protected legally (as a nature reserve) and by predator trapping and carefully controlled visitation. The most common cause of white heron mortality in New Zealand is birds being hit by cars, as many roads pass close to coastal wetlands, and white herons fly low and slow when first getting airborne.

Breeding

Birds arrive at the breeding colony in August. Nests are built in trees and tree ferns up to 15 m high. Adjacent taller trees are used by royal spoonbills. The 3-5 eggs are laid in September-October and are incubated by both parents. Nestlings are fed by partial regurgitation by both parents. Leaving the nest begins with short flights, followed by final departure about 64 days after hatching.

Behaviour and ecology

Males occupying a nest site will defend it against intruders. Courtship displays include shaking twigs gathered from near the nest, preening displays and fanning of the nuptial plumes.

Food

The breeding season at Okarito Lagoon coincides with the whitebait run, and these fish are the primary food during nesting. At other locations their diet includes small fish, frogs, invertebrates and even small birds, which can be caught if they fly too close to a foraging heron. Hunting is usually in daylight, with the bird waiting motionlessly for prey to pass, or walking slowly. White herons will sometimes steal fish from other birds such as shags. The usually feed alone, even when several birds are present at the same site.

Websites

http://en.wikipedia.org/wiki/Great_Egret

http://www.teara.govt.nz/en/herons/page-1

http://www.nzbirds.com/birds/kotuku.html

http://www.whiteherontours.co.nz/

References

Heather, B.D.; Robertson, H.A. 2005 The field guide to the birds of New Zealand. Auckland, Viking.

International Union for Conservation of Nature. IUCN red list of threatened species. http://www.iucnredlist.org (sighted 21 July 2012).

Marchant, S.; Higgins, P.J. (eds.) 1990. Handbook of Australian, New Zealand and Antarctic birds. Vol. 1, ratites to ducks. Oxford University Press, Melbourne.

Oliver, W.R.B. 1955. New Zealand birds (2nd edn). Reed, Wellington.

Robertson, C.J.R. (ed.) 1985. Reader's Digest complete book of New Zealand birds.  Reed Methuen, Sydney.

Recommended citation

Adams, R. 2013. White heron. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

White heron

Social structure
monogamous
Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Nest type
raised platform
Nest description
Pl.tform of sticks and other vegetable matter in the upper parts of trees or crowns of tree ferns
Nest height (min)
7 m
Nest height (max)
15 m
Maximum number of successful broods
Unknown
Clutch size (min)
3
Clutch size (max)
5
Mean egg dimensions (length)
52 mm
Mean egg dimensions (width)
36 mm
Egg colour
Pale green-blue
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Interval between eggs in a clutch
Unknown days
Incubation behaviour
shared
Incubation length (mean)
25 days
Nestling type
altricial
Nestling period (mean)
34 days
Age at fledging (mean)
42 days
Age at independence (mean)
64 days
Age at first breeding (typical)
Unknown
Maximum longevity
22 years
Maximum dispersal
Unknown