Black stilt

Himantopus novaezelandiae Gould, 1841

New Zealand status: Endemic

Conservation status: Nationally Critical

Other names: kāki, kaki

Geographical variation: Nil

Black stilt. Adult standing on one leg. Ohau River delta, February 2011. Image © Glenda Rees by Glenda Rees Glenda Rees (http://www.flickr.com/photos/nzsamphotofanatic/)

Black stilt. Adult standing on one leg. Ohau River delta, February 2011. Image © Glenda Rees by Glenda Rees Glenda Rees (http://www.flickr.com/photos/nzsamphotofanatic/)

Once the common stilt of New Zealand, the black stilt is now critically endangered with a breeding population confined to the Mackenzie Basin of South Canterbury and North Otago. Adults are distinctive in having entirely black plumage, long red legs and a thin black bill, but juveniles and subadults can easily be overlooked amongst pied stilts, while hybrids add to the plumage confusion. Black stilts frequent the wide open braided rivers and associated wetlands of the Mackenzie Basin. There they favour shallow waters of invertebrate-rich sidestreams and pools, wading out into deep water if necessary. Some birds migrate to northern New Zealand harbours.

Identification

Black stilts are a compact stilt, shorter legged and with a thicker bill than the more common pied stilt, which is entirely white below. Juvenile black stilts in their first winter plumage have a black back, smudgy grey hind neck and variable dark markings on the flank. This plumage darkens in their second summer moult, and by mid-summer they are predominantly black. Adult hybrid stilts have a distinctive black band across their breast, the width of black generally correlating with the amount of black stilt genes in the individual.

Voice: contact calls are a single or repeated “yep” call not unlike that of pied stilt. Territorial birds are noisy, having a higher pitched and more penetrating call than the pied stilt.

Similar species: both species of stilts are immediately separable from oystercatchers by the presence of a relatively thin black bill and long thin red legs, as opposed to oystercatchers possessing long thick, red bills and short, thick red legs.

Distribution

Black stilts were formerly widespread throughout New Zealand, and were still breeding at North Island locations in the late 19th century. During the 20th century the range contracted from being South Island wide to being confined to Canterbury and Otago in the 1950s, South Canterbury-North Otago by the 1970s, and the Mackenzie Basin by the 1980s. Breeding pairs are now confined to the area  between the Lake Tekapo and Lake Pukaki basins in the north to the Ahuriri River in the south.

Outside the breeding season most black stilts move locally within the Mackenzie Basin, but small numbers visit  the Canterbury coast e.g. Lakes Wainono and Ellesmere and north to Kawhia and Kaipara harbours in the North Island.

Habitat

Typical breeding habitat for black stilts comprises combinations of braided riverbed habitat and nearby wetlands such as swamps, ponds and shallow edges of lakes. Within this mosaic, nesting territories are located in areas with abundant food, e.g. a main river channel if invertebrates such as the mayfly (Deleatidium) are abundant. Alternatively, more stable side-streams, swamps or ponds may be favoured particularly when there has been flooding and scouring of the main river courses.  Black stilts will leave their territory to feed in other habitats at sites that are a kilometre or more away

Population

The total population currently numbers c.100 birds, including captive birds that are intensively managed.

Breeding

Black stilts breed mainly in pairs but they can also associate with other pairs of black stilts and colonies of pied stilt. Typically pairs are solitary and territorial, defending their territories against other stilts, and sometimes other waders, if they venture close to chicks. Birds begin to arrive on the breeding grounds and set up territories in July (but often travel daily back and forth to their feeding areas of the last few months). First eggs are laid in September to October, in lined nests in vegetation clumps, open banks, or small depressions. The clutch-size is nearly always four eggs coloured with a green to olive background and with bold dark streaking and blotching. Incubation is performed by the male and female for c.25 days and chicks fledge after another 4-8 weeks. Black stilts first breed at 2 or 3 years of age.

Most eggs and chicks are lost to mammalian predators, e.g. mustelids (ferrets and stoats), cats, hedgehogs and rats; also natural causes including flooding and harrier predation. A sensitive period can be after sudden declines in the abundance of the mainly rabbit prey of mustelids and cats. Past declines were sometimes sudden and not explained by habitat loss, e.g. some big losses occurred in the 1950s coinciding with extensive rabbit control. Locally habitat loss has also been a factor. Hybridisation with pied stilts (which have similar courtship) and resulting hybrids further complicates the recovery process. Nearly all wild black stilts stem from intensive management, especially captive management.

Behaviour and ecology

Black stilts are closely adapted to the New Zealand braided riverbed environment and, unlike the pied stilt, are able to exploit prey seeking refuge beneath riverbed stones and can continue to forage in the river whereas pied stilts may opt to depart. This low level of prey activity occurs at high lighting levels (sun high in sky) and when water temperatures are low (e.g. early in morning). They will also take advantage of emergence events of invertebrates, most notably that of the mayfly Deleatidium spp.

Food

Black stilts are carnivorous. Inland birds prey mainly on insect larvae, but they take a range of other prey including fish, molluscs, crustaceans and worms, and some terrestrial prey e.g. spiders. In coastal habitats black stilts take a variety of crustaceans, molluscs and worms. They often feed by scything for worms and midge larvae and other prey in soft substrates, particularly if visibility is impaired by waves, rain or darkness (they often feed at night).

Weblinks

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

http://www.doc.govt.nz/conservation/native-animals/birds/wetland-birds/black-stilt-kaki/

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

http://www.nzonscreen.com/title/the-black-stilt-1983

References

Heather, B.D.; Robertson, H.A. 1996 (rev 2000). The field guide to the birds of New Zealand. Viking,Auckland.

Marchant, S.; Higgins, P.J. (eds) 1993. Handbook of Australian, New Zealand and Antarctic birds. Vol. 2, raptors to lapwings. Oxford University Press, Melbourne.

Pierce, R.J. 1983. The changed distribution of stilts in New Zealand. Notornis 31: 7-18.

Pierce, R.J. 1984. Plumage, morphology and hybridisation of New Zealand stilts Himantopus spp. Notornis 31: 106-30.

Pierce, R.J. 1987. Differences in susceptibility to predation between pied and black stilts (Himantopus spp.). Auk 103: 273-80.

Recommended citation

Pierce, R.J. 2013. Black stilt. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

Black stilt

Social structure
monogamous
Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Nest description
Ground nest constructed of plant material and small stones.
Nest height (mean)
0 m
Clutch size (mean)
4
Clutch size (min)
3
Clutch size (max)
6
Mean egg dimensions (length)
45 mm
Mean egg dimensions (width)
32 mm
Egg colour
Greenish or olive with bold blotches and streaks
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Interval between eggs in a clutch
1-2 days days
Incubation behaviour
shared
Incubation length (mean)
24-27 days
Nestling type
precocial
Nestling period (mean)
< 1 day
Age at fledging (mean)
28 to 56 days
Age at fledging (min)
28 days
Age at fledging (max)
56 days
Age at independence (mean)
6-8 months
Age at independence (min)
180 days
Age at independence (max)
240 days
Age at first breeding (typical)
2-3 years
Maximum longevity
15 years
Maximum dispersal
Migratory to northern North Island, about 600 km