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The ecology and reproductive biology of the European goldfinch, Carduelis carduelis near Melbourne, Victoria
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posted on 28.05.2018by Alexander L. A. Middleton
Between December, 1962, and August, 1965, the ecology and reproductive biology of the European Goldfinch Carduelis carduelis was studied in the vicinity of Melbourne, Victoria, in an attempt to assess the role of this exotic species in the Australian environment.Throughput the year, field observations were made on all aspects of the goldfinch’s annual cycle. During the non-breeding season (January to late August) the goldfinch occupies an open habitat where large feeding flocks are common at all times of day. In early September the winter flocks break up, and the birds gradually return to the nesting areas. After a nest site has been selected by the female, small territories are established by the pair. Nests, situated almost exclusively in exotic shrubbery, are built between late September and late January. Clutch size at Melbourne is 4.8. The incubation and nestling periods average 13 and 15 days respectively. Egg hatched in 50% of the nests in which eggs were laid, but only 28.9% of these nests produced fledglings. The major causes of nest failure are predation, wind action, and desertion.The nesting study was supplemented by a histological examination of the gonads and associated organs of 307 male and 205 female goldfinches. The results indicate that gonadal activity is cyclical. Gondal recrudescence starts in both sees in July, one month after the winter solstice. Breeding condition is research reached in September and persists until January when the gonads regress quickly. By March the gonads have reached their quiescent winter condition. The study of the male seminal sacs, in conjunction with the results of testicular examination suggest that spermatogenesis may occur in waves during the breeding season. The changes in bill pigmentation, observed throughout the year, bear a clear relationship to the gonadal cycle.The moult sequence in the goldfinch is described in detail. Moult, which is an annual process, starts in December, reaches its peak in February and March, and is completed by mid-May. There is a clear overlap between moulting and nesting.The food of the goldfinch was assessed by an examination of the crop and gizzard contents of 20 specimens from each month of the year, and by field observation. A total of 32 plant species were identified, only one proved to be an Australian native. Small quantities of insect food are eaten at all times, but there is a marked increase in the occurrence of insects in the crop during the breeding season.Finally the topic of introduced species is briefly discussed in the light of recent investigations. This topic is then related to the Goldfinch has succeeded in Australia because of its ability to exploit a vacant, man-made niche for which there were no competitors.