Breeding biology of North Island robins (<em class="sciname">Petroica australis longipes</em>) on Tiritiri Matangi Island, Hauraki Gulf, New Zealand

We studied North Island robins over 7 breeding seasons following their reintroduction to Tiritiri Matangi Island. All robins bred in their first year if a mate was available. They usually retained pair bonds for life but some females switched mates within or between breeding seasons. There were 2 instances of sequential polyandry, where a female laid a clutch with a new male while her previous mate was rearing her fledglings. The 1st clutches were usually laid in early September and the last clutches in late December or early January. Mean clutch size was 2.3 eggs, and clutches were largest in the middle of the breeding season. Females reared a maximum of 3 broods per year, and a maximum of six fledglings. Females that survived the breeding season fledged an average of 2.48 young, and 51% of clutches found before hatching fledged at least one young. Juveniles were fed for 47 weeks after fledging, and stayed in the natal territory for 7-10 weeks. Dispersing juveniles were often chased when entering other territories, but there were 4 instances of juveniles being fed by unrelated lone males. The juvenile survival rate declined as the population grew. Permanent territories were restricted to patches with a canopy of at least 6 m, totalling about 13.4 ha, and the breeding population levelled off at 65 in the 5th year. The decline in juvenile survival was similar for males and females, suggesting that both sexes needed to compete for territories even though there were always males without mates because of an initial bias in sex ratio. Males had delayed plumage maturation whereby they appeared similar to females or juveniles until after their first breeding season. We suggest this could be advantageous for territory acquisition because male territory holders cannot be preferentially aggressive toward juvenile males. Armstrong, D.P.; Ewen, J.G.; Dimond, W.J.; Lovegrove, T.G.; Bergstrom, A,; Walter, B. 2000. Breeding biology of North Island robins (Petroica australis longipes) on Tiritiri Matangi Island. Notornis 47(2): 106-1 18.