About Anarhynchus frontalis Quoy & Gaimard, 1832
Anarhynchus frontalis, commonly called the wrybill, is a small, plump plover. It measures 20 to 21 cm (7.9–8.3 in) in length and weighs between 43 and 71 g (1.5–2.5 oz). Its plumage shows slight sexual dimorphism. Males have a white forehead, pale grey crown, nape, back, wings and tail, and white throat, breast, belly and rump, with a thin black band across the breast. In females, this breast band is thinner. In non-breeding season, the band is much less distinct in both sexes. Males also have a small black bar between the white forehead and grey crown, which is absent in females; like the breast band, this marking is reduced in the non-breeding season. The wrybill's most distinctive feature is its long black bill, which is always curved to the right. It is the only bird species with an asymmetrically turned bill. Wrybill eggs are very pale grey, covered in very small brown spots that blend well with surrounding shingle. In addition to the eggs being well camouflaged, adult birds and chicks are very difficult to see when standing still. Chicks have very pale grey upper bodies with black speckles, and white lower bodies. The wrybill's vocalizations have distinct forms: a short weet, given in flight to signal alarm; a harsher call for signaling greater alarm; a chirring sound used to challenge aggressors; and a high-pitched short peep used by fledglings and juveniles. The wrybill is endemic to New Zealand. It breeds on large braided rivers in Canterbury and Otago, South Island, preferring large dynamic rivers that do not become overgrown with weeds. Its main breeding rivers include the Waimakariri, Rakaia, Rangitata, Waitaki and Ashley. It once occurred more commonly on smaller rivers, but has undergone a range contraction, and now only occupies around 60% of its estimated original range. After breeding, from around late December to early February, the species leaves its breeding sites and migrates to shallow estuaries and sheltered coastal areas in the North Island, including the Firth of Thames, Manukau Harbour, Kaipara Harbour and Tauranga Harbour. Wrybill moulting occurs between December and May. The moulting process advances quickly at the start, when the first feathers are dropped, and slows as the longer outer feathers begin to grow. Migration away from breeding grounds starts in November with the earliest fledged birds. Adults follow in January–February after breeding is complete, along with the remaining fledglings. Migration back to South Island breeding sites occurs in August. The current total population of wrybills is around 5000 individuals.
