Breeding of South Island pied oystercatchers (Haematopus ostralegus finschi) on farm land in mid-Canterbury, New Zealand

Abstract

Breeding of South Island pied oystercatchers (Haematopus ostralegus finschi) on farmland in mid-Canterbury was studied from 1987 to 1997. Each year birds returned to breeding territories from early June; females arrived about six days earlier than males. Laying dates extended from early August to mid-November and were similar in all years. Most first clutches were laid from late August to mid-September. Up to two replacement clutches were laid. Clutch size averaged 2.29 (range 1-3 eggs) and declined through the breeding season, but was consistent from year to year. Mean first clutch sizes were larger than replacement clutches. On average, 47% of eggs hatched and 59% of these chicks survived to fledge. Both hatching and fledging rates declined through the season. On average, 52% of pairs which laid in any year failed to rear a fledgling. Hatching success was greater in cultivated sites than pasture sites, but fledging success was similar at both sites. Trampling by stock, farming activities, and unknown causes were the main causes of egg loss.