Milk Intake of Elephant Seal Pups: An Index of Parental Investment

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Abstract
Total milk ingested throughout nursing in free-living northern elephant seal pups, derived from the turnover of tritiated water, gives an accurate estimate of the energetic component of parental investment. In 4 wk of nursing, females transferred a mean of 138 kg of milk with a value of 6.04 .times. 105 kcal, 5 times the metabolic requirements of pups. The mean rate of energy transfer is more than twice that predicted for the female''s size from studies of laboratory and domestic animals. In 1 mo., pups receive sufficient energy and essential nutrients from mother''s milk to enable them to fast while continuing to develop for an additional 2.5 mo. before feeding on their own. Measurement of the energetic component of parental investment makes it possible to test predictions from the theory of parental investment.