Growth, Body Components and Energy Content of Nestling Double-Crested Cormorants

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Abstract
Development of altricial double-crested cormorant [Phalacrocorax auritus] nestlings involved changes in weight gain, external dimensions, organ weight, body composition and caloric density; and the normal pattern of growth is described here in detail. Weight gain was unusually rapid for a large bird, and leveled off below adult weight. External dimensions grew in length proportionally more than in smaller species. As is typical of small altricial birds, the internal organs of cormorants grew more rapidly than the body as a whole in the early stages of the nestling period. Water content of tissue declined through the growth period as in other altricial birds, but fat content increased more in the cormorant. Live weight caloric density increased linearly from about 0.65 kcal/g to about 2.2 kcal/g. Live weight caloric density for any altricial species can be estimated as rising from 0.7 kcal/g at hatching to about 2.0 kcal/g at fledging. Compositional analysis is required for caloric estimations in precocial and semiprecocial species, however. Comparison of organ growth showed that precocial birds hatch at a more completely developed stage than altricial and semi-precocial species.