signal alarm, and a harsher call is used to signal greater alarm. A chirring sound is used to challenge an aggressor. Fledglings and juveniles have a high-pitched short peep. Distribution and habitat The wrybill is endemic to New Zealand. It breeds on large braided rivers in Canterbury and Otago, South Island, preferring large dynamic rivers that will not become overgrown with weeds. The main breeding rivers include the Waimakariri, Rakaia, Rangitata, Waitaki and Ashley. It used to occur more frequently on smaller rivers, but has undergone a range contraction, and now only occupies around 60% of its estimated original range. After breeding, around late December till early February, they leave their breeding sites and migrate to shallow estuaries and sheltered coastal areas in the North Island. These areas include Firth of Thames, Manukau Harbour, Kaipara Harbour and Tauranga Harbour. Behaviour Wrybills like to roost in large flocks during winter which differs greatly from breeding time when they become very territorial towards other birds. They usually roost on one leg and hop away when approached too close. Wrybills are known to perform large aerial displays with their flocks. This usually happens shortly before the migration south. Breeding Wrybills form monogamous bonds with their mates and will return to the same territory each year to breed again. If their mate does not return, the bird will move territories. Nesting territories are strongly defended. These can be anywhere between 1 and 11 hectares in size, with an average size of 5 hectares. They show strong philopatry to their territories, and young birds show strong philopatric tendencies towards breeding close to where they were hatched. Many breeding pairs will lay two clutches in a breeding season, especially if the first clutch was destroyed by flooding or predators. Nesting sites are shallow scrapes in areas of large stones or sand. The clutch size is two eggs, which are incubated by both parents (but more so by the female) for 30 to 36 days. The chicks have downy feathers on hatching, grey to off-white above and white underneath. Both parents attend to the chicks, which fledge after around 35 days and are immediately independent after this. Young birds start breeding when they are two years old. Ecology Moulting of wrybills happens between December and May. The moulting process advances quickly at the start of the process, when the first feathers are dropped, and slows as the