BIOLOGY OF THE BANK CORMORANT, PART 5: CLUTCH SIZE, EGGS AND INCUBATION

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Abstract
Cooper, J. 1987. Biology of the Bank Cormorant, Part 5: Clutch size, eggs and incubation. Ostrich 58: 1–8. The Bank Cormorant Phalacrocorax neglectus, a marine species endemic to southern Africa, produced a clutch of one to three eggs (mean clutch size 2,02; modal clutch size two). Clutch size did not vary through the breeding season or with replacement laying. Mean egg dimensions were 59,0 x 38,4 mm (50,4 g). Mean egg mass loss during incubation was 9,4%. Egg size decreased with order of laying, the third eggs of three-egg clutches being the smallest of all. Mean egg size increased and then decreased through the season. Eggs comprised 13,3% shell, 17,5% yolk and 69,3% albumen and had a mean energy content of 207 kJ. Both sexes incubated, by placing the eggs on their webbed feet. Eggs hatched asynchronously in the order they were laid. The mean laying interval (3,0 d) and hatching interval (2,7 d) did not differ significantly. Laying-hatching intervals averaged 29,6 d and decreased with order of laying, suggesting that full incubation did not commence with the laying of the first egg. Mean hatching period was 1,2 d. Replacement clutches were laid 79 ± 51 d after failed first clutches were laid and 52 ± 33 a after clutch failure. Temperatures averaged 33,4°C in freshly laid eggs and 27,7°C in nests. The unusually small clutch size is not related to the species producing relatively large eggs.