Breeding biology of the Olive-backed Oriole Oriolus sagittatus on the mid-north coast of New South Wales

Abstract

Although Olive-backed Orioles Oriolus sagittatus range widely through northern and eastern Australia, their breeding biology is poorly known. Data from 14 nests were recorded during three breeding seasons (in the period 2009–2012) on the mid-north coast of New South Wales. Nests were located in the outer foliage of four species of tree, between 1.7 and 9.8 m above the ground. Mean clutch-size was 2.3 eggs. Incubation was undertaken only by the female, and nest-attentiveness during incubation varied between 58 and 88%. The mean incubation period was 16.2 days, with hatching occurring synchronously in some nests and asynchronously in others. Similarly, brooding was also undertaken only by the female up to and including the sixth day after hatching, with nest-attentiveness during the nestling period ranging from 73% on the day of hatching to 15% on Day 6 post-hatching. The mean combined interval between feeding visits to the nest was 15.0 minutes, with a feeding visit rate of 4.0 h^-1. Both males and females fed the nestlings although feeding effort by each varied considerably between individual nests. For nestlings fledging naturally, the mean nestling period was 15.0 days. Nest success was 80%, with an average 1.5 fledglings per nest. Once fledged, young Orioles remained within 70 m of the nest for up to 24 days and were fed at a rate of 3.3 visits h^-1. Behaviour and vocalisations of the adults and young birds are also discussed. Data presented here fill a gap in the knowledge of this species within Australia, and are compared with available data for the only three species (out of a total of 33 species) within the Oriolidae family that have been studied in detail.