Birth to weaning in 4 days: remarkable growth in the hooded seal, Cystophora cristata

A brief lactation period with rapid neonatal weight gain may be adaptive for seals breeding on unstable pack ice. We studied the duration of lactation and growth of known-age pups of the hooded seal, Cystophora cristata, on the pack ice off Labrador. Mean body weight of pups increased from 22.0 kg at birth (n = 21) to a maximum of 42.6 kg on day 4 (n = 11) and then declined. On the basis of maternal absence, weight change, gastric contents, and clarity of blood serum, we conclude that pups are weaned 4 days after birth (range, 3–5 days). This is the shortest lactation period known for any mammal. Tagged pups captured on sequential days gained on average 7.1 kg per 24 h from the day after birth to weaning. Maternal effort supported a relative rate of weight gain (145 g∙kg maternal weight−0.75∙day−1) that is 2.5–6 times that of other phocids. By combining a large birth weight with rapid neonatal weight gain, hooded seals achieve a weaning weight comparable to other phocids in one-third to one-tenth the amount of time after birth.