Wrybill

INTRODUCTION:
The Wrybill is the only bird in the world with the bill tip curving to the right. This “tool” is adapted to the feeding behaviour of this species when the bird extracts insects and aquatic preys from rock crevices and under stones. The Maori name is Ngutuparore.

DESCRIPTION OF THE BIRD:
Biometrics:
Length: 20-21 cm
Weight: 55 g

The adult male has ashy-grey upperparts, including wings and tail. The rump is white.
The underparts are white on chin, throat and belly. We can see a black breast band.
On the head, crown and nape are ashy-grey. In breeding plumage, the white forehead shows a black frontal bar. Lores, eye area and ear-coverts are ashy-grey.
The black bill is bent to the right in the middle. The eyes are dark brown. Legs and feet are greyish-green.

CALLS AND SONGS: SOUNDS BY XENO-CANTO
The Wrybill gives short, high-pitched “tweeps” in flight, before landing. This bird does not call frequently.

BEHAVIOUR IN THE WILD:
The Wrybill feeds on aquatic invertebrates during the breeding season such as worms, annelids and gastropods, and also mites, spiders, and eggs, larvae and pupae of numerous insects, including the adults. It also feeds on crustaceans, fish and their eggs.

It uses its curved bill to extract the preys from rock crevices and under stones. It tilts the head to the left while pushing the bill under a stone, thanks to the bill curvature. Then, the bill is moved forwards and to the right.

The Wrybill is migratory. It breeds in C South I and moves after the breeding season to the mudflats of estuaries and harbours on N North I. They migrate along the E coast of South I and the W coasts of North I. The adults show strong site-fidelity to their wintering grounds.

The Wrybill can suddenly take flight, performing rapid wingbeats which produce vibrations.

PROTECTION / THREATS / STATUS:
The Wrybill has small population estimated at 3,000/3,300 mature individuals.
It is threatened by deterioration of the habitat due to the encroachment of weeds with reduction of the water flow.
Predation by gulls, stoats and cats is probably substantial too. The increasing use of riverbeds for recreational purposes and floods are also important threats.
The Wrybill is currently listed as Vulnerable.

The female is duller, with browner and narrower breast band, and she lacks the black frontal bar.
The juvenile resembles non-breeding adult. It has grey patches on breast sides instead of black breast band. On the upperparts, the feathers show narrow black subterminal bands and narrow white edges.
The non-breeding adult has indistinct or lacking black breast band and no frontal bar.

RANGE:
The Wrybill is found in New Zealand. It breeds in C South I and winters in N North I.

HABITAT:
The Wrybill breeds inland on large, fast-flowing rivers running in bare beds of shingle and sand. Occasionally, it may breeds in smaller, slower-running rivers.
Outside the breeding season, it frequents shallow estuaries and sheltered coasts with large mudflats and muddy lagoons.
It may occasionally frequent ploughed areas and muddy shores of small lakes and ponds in mountains.

But on intertidal mudflats, the Wrybill tilts the head to the left and performs sideways sweeps with the bill, usually from right to left, in order to sieve preys from water and mud.
It often forages in shallow pools, in shallow water in shingle riverbed, on intertidal mudflats and along riverbanks.

The Wrybill is monogamous. Nesting and feeding territories are usually strongly defended.
The mating season starts when the birds return to South I. They are very active, chasing each other in the air and on the ground. If the pair is disturbed during the courtship displays by another bird, the intruder is driven away by the bird of the same sex. It runs after it with outstretched neck among the stones, while maintaining its balance by slightly opening the wings.
The female shows great submission to the male once mated. They nest solitary in loose colonies with nests at least 400 metres apart, and never less than 40 metres.

REPRODUCTION OF THIS SPECIES:
The laying starts in mid-September and continues throughout October. A second clutch may occur from November to late December.
The Wrybill’s nest is on the ground, in sand, among large, smooth, rounded stones. It is protected by a piece of wood or a larger stone. Occasionally, small pebbles are added around the edges of the nest, as lining for the eggs.

The female lays 2 eggs very similar to the stones among which they are laid. Both adults share the incubation and take turns during 30-36 days. Their plumage allows them to be invisible in such habitat.
At hatching, the chicks have white to grey upperparts with darker markings, and white underparts. They leave the nest within a day of hatching. They follow their parents and forage for food with them. They fledge 35-37 days after hatching.

The adults may perform the typical “broken-wing display” to lure an intruder away from the nest. The rump feathers are raised and the tail fanned and depressed, while the bird produces a continuous purring noise.