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In each of the five years, 1987 to 1991, a pair of Grey seals Halichoerus grypus produced a pup. For each birth the mother and pup were kept under constant observation and a variety of suckling parameters were recorded. In January 1991 the pup was born in an indoor suckling enclosure where in 1987 and 1990 other infants had been reared. Most suckling sessions were initiated by the pup vocalizing followed by the mother presenting her nipples. The pup ended 89% of the sessions. Throughout the 17-day suckling period, total daily suckling time, suckling session length and number of pauses in suckling sessions all increased. The length of non-suckling intervals decreased. Even in the absence of vocalizations the mother appeared to be able to judge when the pup wanted to suckle, probably alerted by the waking-up behaviour of the infant. The ♀ flippered before 43%, during 41% and after 76% of all suckling sessions. The pup flippered before 12%, during 13% and after 17%) of the suckling sessions. The mother's food intake was low for a few days immediately before and for three days after the birth. After this her food intake increased to 5 kg per day until day 9, then decreased to 0–5 kg one day before weaning. The ♀ ate more after weaning and copulation than during the suckling period when she lost a mean 3 kg per day. The pup gained a mean 2 kg per day and by day 43 he began to catch live fish. When the pup started to eat thawed marine fish the colour of his mystacial vibrissae started to change and about two weeks later they went from black to transparent. At the age of 120 days the pup was released into the North Sea to join a group of wild Grey seals.