Notes on the breeding of the Pied Cormorant near Werribee, Victoria, in 1971, 1972 and 1973

Abstract

Breeding data are presented for what is apparently the only permanent colony of Pied Cormorants in Victoria. Information relating to clutch-size, hatching and fledging success is given for 1971, 1972 and 1973 breeding seasons. Dimensions of eggs and data relating to nests are also given. Nest-building and egg-laying were initiated in mid May each year, with most eggs being laid by late July. Laying in 1972, when most complete observations were made, was characterized by an initial peak before mid-June and a subsequent but lower peak between mid-August and early September. Hatching started in mid-June and followed the bimodality imposed by egg-laying. Clutch-size varied between 1 and 5, but was on average 3.32 eggs (n = 256, S.D. ± 0.77) for the three seasons. Variation in average clutch-size between seasons were also noted and it was found that early (before mid-August) clutches were slightly bigger and more successful than those laid later. Clutches from which young hatched were also bigger than those from which no young were raised. For 162 clutches in 1971 and 1972 followed through to the fledging of young, an average of 3.15 eggs produced 1.36 young of which 0.83 fledged. The breeding season is discussed with respect to the physical environment and data relating to availability of potential food. Samples of food taken from the young in the nest suggest a. tentative connection between the local abundance of clupeoid fish and the winter and early spring breeding season.