This member of the family Charadriidae or plovers is unique among all birds in that its bill is turned wholly to one side. Species with bills curved vertically upwards or downwards or even crossed are relatively commonplace, but the manner of deflection of the wrybill's beak sets this species entirely apart. Furthermore, it is confined to the two main islands of New Zealand and, even here, its distribution is unusual. The only known breeding grounds are the shingly beds of a number of rivers of the eastern South Island from southern Marlborough to northern Otago. From December to May a northward migration takes place and the species winters on beaches and mudflats – mainly in the Auckland Province in such places as the Firth of Thames and the harbours of Manukau, Kaipara, and Parengarenga. Immature birds remain in the north when the return migration takes place from July to September.
The wrybill bears a superficial resemblance to the related and common banded dotterel: both are approximately the same size; there is the appearance of a cap to the head; the upper surface of the body is dark and the under surface white; and the chest is banded during the breeding season. There are, however, important differences in detail. The body shape of the wrybill is characteristically dumpy, its upper plumage is bluishgrey, across the chest is a single black band which is narrower and less intense in the female than in the male, and legs and feet are a blackish-green. The black bill is curved to the right.
On arrival at the breeding grounds in August, wrybills have assumed their full breeding plumage. After courtship display and mating the wrybills make nests which are mere scrapes in the midst of a wide area of clean shingle and large stones close to water. Two eggs comprise the usual clutch. These are laid between September and November and are pale greyish-green, minutely speckled, and scored with black. Incubation is shared. Both eggs and birds blend beautifully with their surroundings.
Though little studied, the food of wrybills is generally similar to that taken by other waders – small crustacea, molluscs, worms, and insects. In spite of much speculation, the adaptive advantage – if any – of the laterally turned bill (obvious even in the unhatched chick) is unknown.
The common call is a sharp “weet” given with a rising inflection, and the alarm note is a low churring. Among New Zealand waders, wrybills are notable for their lack of fear of man. The Maori name for the bird is ngutu-parore.
by Gordon Roy Williams, B.SC.(HONS.)(SYDNEY), Lecturer in Agricultural Zoology, Lincoln Agricultural College.