We’ve mentioned that the study site is now quieting down and thinning out a little; this is a product of the short lactation period of the grey seal. After grey seal mothers give birth, they only feed their pup for an average of 16-18 days. Once this period is over, the mothers ‘wean’ their pups very abruptly and return to the sea after mating.
Without mum around, the weaned pups (‘weaners’) must learn to fend for themselves; strangely, they don’t immediately head to the sea to find more food. Instead, they stay on land for up to three weeks, often grouping together into weaner ‘gangs’. These gangs tend to hang out in areas away from the higher densities of adults, probably to avoid aggressive interactions with the testosterone-pumped males, and the mums looking to protect their own pups and prevent ‘milk theft’.
Weaners fast during this time, gaining their energy from the blubber that they put on during lactation (at a rate of almost 2kg per day!). Some have suggested that the weaners fast to get rid of some of their blubber so that they are not too buoyant to dive efficiently. However, the adult females only have a limited amount of energy during the breeding season as they also fast during this time, so why should they give their pup excess energy that will just be wasted?
This has prompted researchers to suggest possible functions that the period of on-land fasting might have. It seems to allow weaners to develop more efficient oxygen storage and transfer in the blood and muscles (as shown by changes in their blood). Combined with muscular development this might make the weaners better divers and swimmers when they finally leave the colony.
As adults, grey seals are very ‘faithful’ to their birth site and previous pupping sites; it has also been speculated that the time on land post-weaning allows some kind of ‘learning’ of the birth site. This learning could help them to find their way back in later years.
For now, we’ll just have to add the function of the on-land fast to our list of interesting questions to answer, and accept that all we really know for now is that these gangs of weaners have turned getting to our hides each morning into a gauntlet run of hissing and snapping (though endearing) new pups.