Ardea
Official journal of the Netherlands Ornithologists' Union

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Pomeroy D.E. (1977) The biology of Marabou Storks in Uganda. I. Some characteristics of the species, and the population-structure. ARDEA 65 (1-2): 1-24
The plumage and soft parts of Marabou Storks are described in some detail. The colour of the back and main flight feathers were most useful in separating age-classes but other characters can be used as well (Fig. 3, Table l). Amongst adults there is an annual cycle (Fig. l) involving the colour of the back and the presence of broad white edges to the secondary covert feathers. Breeding adults have a waxy 'bloom' (Plate l) on the feathers of the back. Moult is protracted, lasting for more than a year in the case of the secondaries (Fig. 2). Feathers tend to be shed sequentially but there are many irregularities. Males are larger than females (Figs 4, 5; Tables 2, 3). Of more than 70 birds dissected all whose wing-length plus tail-length exceeded 100 cm were males (Fig. 4). The bill, which is very long, is not fully-grown until about two years after fledging (Fig. 6). The bursa of Fabricius apparently regresses with the onset of sexual maturity (Table 4) although in a few individuals it may not disappear completely. From counts of the breeding population and the total Ugandan population a model of the age-structure of the population can be deduced (Fig. 10, Table 7). The model implies that breeding begins at about 6 years of age, some 3 years after reaching sexual maturity. Annual mortality-rates for adults are estimated at about 8%. There is an annual cycle in gonad weights (Fig. 7); but out-of-season regression is incomplete. The average clutch-size is 2.7 eggs (Table 5). Changes in the total numbers of birds in two areas where they congregate (Fig. 8) reflect regular seasonal movements. After the breeding-season, birds disperse (Fig. 9). The main nonbreeding populations come from the North and consist mostly of males (Table 6).


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