Breeding biology and development of the young of Manorina melanocephala, a communally breeding honeyeater

Abstract

The Noisy Miner is a communal breeder: many individuals participate in activities at each nest. However, much of the species's behaviour and social organization is unique, even among communal breeders. Marked populations were observed in southeastern Queensland between 1969 and 1974 but most data are from one intensely studied area in 1972, with additional data from 1971 and 1973.

In this study area of seven hectares, 137 birds were colour-banded. The resident population declined in the three years from 9.0 to 7.7 birds per hectare. The sex ratio favoured males by as much as 3.3:l. Most breeding occurred between July and November. The onset of nesting varied from year to year and could not be easily related to environmental variables. Most nests were built in sites that did not afford much concealment. The height of nests varied but preference was not shown by particular females. Successive nests tended to be higher, effected by females selecting higher trees. Spiders' web land silk from cocoons was used in the construction of nests. The female built the nest and advertised its position with a flight display. Previous nests were dismantled and used in the construction of the nests. Building visits averaged 8.7 per hour and as many as seven males visited a nest at this stage. Females did not visit other nests. Males visiting the nest of an incubating female were all found to be producing spermatoza and at any time of year probably some males in a population are producing sperm. In some years some adult females made no nesting attempts.

Clutches varied from one to four and averaged 2.64 eggs. The iirst egg was laid in fewer than three days or more than nine after completion of the nest. Eggs were laid one each day usually, in the early morning, and females began to sit after the second egg was laid. Only one female incubated and incubation took sixteen days. Attendance at the nest by females at different stages in incubation averaged from 35.2 to 41.2 minutes per hour.

The mean brood size was 2.52; 15.9 per cent of eggs, excluding those lost, failed to hatch. The nestling period was about sixteen days. Only the female brooded.

Fledging proceeded over several days, the young gradually moving out on supporting branches in the day and returning to the nest at night. Once away from the nest, the young made their way to the top of a tree. They were highly vocal in soliciting food. When fed, the wings were not quivered, perhaps a behaviour counteracting the high activity of feeding adults. Feeding rates at this stage were as high as 87.8 times per hour. Juveniles between twenty-six and thirty days from the nest were lirst threatened by adults. Between thirty-one and thirty-five days, they began to utter a quiet warbling subsong. Attacks by adults became more frequent and reached their greatest intensity between fifty and seventy days. Both males and females attacked juveniles.

Nest success was very low, less than ten per cent in each of the three years. Even if some nests were never laid in, success calculated to exclude this possibility was still no greater than 16.7 per cent in any year. Some loss could be attributed to wind and storms; presumably the remainder was through predation or activities of the Miners themselves. A new nest was usually started when a female lost eggs or nestlings, in one case in fewer than sixty hours.