The Reproductive Behavior of the Bell Miner Manorina melanophrys

Abstract

Bell Miners in three study colonies at Bundoora, Victoria, were monogamous. All breeding pairs were assisted in rearing of young by helpers. No extra-pair copulations were observed and it is unlikely that helpers contributed genetically to broods they aided. Breeding occurred in every month of the year and individual breeding pairs made successive attempts within a year. Individuals were capable of breeding nine months after fledging and did not appear to delay breeding to the same degree as many co-operative breeders. Breeding vacancies were filled rapidly. Male breeding vacancies were generally filled by individuals from within the colony whereas female breeding vacancies were filled by individuals from other colonies. Males were occasionally observed to feed their mates before copulation. Mate guarding by both sexes occurred when a new pair- bond was being formed and during the period of nest construction. Nests were built by the female breeder. The mean time- interval between commencement of construction and the laying of the first egg was 7.8 ± 1.3 days. The average clutch size was 1.91 ± 0.07 eggs. Incubation was performed by the female over a mean total period of 14.4 ± 0.3 days. The mean number of days between the hatching of the last egg and the fledging of the last nestling was 11.7 ± 0.7 days. Dependent young continued to be fed at a decreasing rate by parents and numerous helpers (up to thirteen) up to an average of 10.6 ± 1.9 weeks after fledging. The mean number of young fledged per attempt was low (0.62 ± 0.22) and highly variable. The major cause of juvenile mortality was predation. Food did not appear to be limiting and there was no evidence of starvation. The large variability in the outcome of a reproductive attempt may have led to the degree of multi-broodedness in Bell Miners and male offspring being philopatric.