One of the many interesting behaviours we’ve observed in grey seals is the act of fostering. In some cases, when a mother loses or abandons her pup she adopts another. Happily, in some cases this can result in an already abandoned pup finding a foster mother. However, this can also result in some pups being stolen from their related mothers. An example of this ‘pup theft’ phenomenon involved one of our study animals, 6J. She faced a longstanding rivalry from another mother over her pup resulting in some intense squabbles at a muddy wallows we call ‘OJs pool’, one of our main study sites. Interestingly 6J seemed to be with her pup in the mornings and then be displaced by the rival female in the afternoons. This made for interesting watching as well as useful data regarding heart rate changes in response to biotic stress!! The pup seemed to favour 6J during times of conflict, but once settled was content to suckle from either mother.
As behavioural and evolutionary ecologists, events such as these raise many questions. The pup had found a new mother to nurse it and raise it until weaning, all fine and well for the pup, but from an evolutionary perspective begs the question, why would the true mother stick around? The interaction between mother and pup can be simplified to a direct transfer of energy during weaning. This ‘energy’ is accumulated by the mother throughout the year in order to be able to fatten the pup to the best of her ability. As with all behavioural interactions this represents a trade-off. In this case the trade-off is between the mother investing maximally in this pup without having a detrimental effect on her future pups through loss of condition which would affect her ability to nurse them. Within these parameters it seems nonsensical that 6J should invest energy in trying to regain this year’s pup, to the detriment of her future offspring, when it has a perfectly strong chance of survival with its ‘new’ mother which would allow 6J to pre-emptively focus on gaining energy with which to transfer to future offspring.
This scenario, from an evolutionary perspective, also brings into question the foster mother’s motivation to nurse an unrelated pup. This acts to the detriment of her future offspring without the advantage of increasing the spread of her own genes, so seemingly represents an enormous evolutionary flaw that should be lost from the population! However, this behaviour is not uncommonly observed. It is likely that this behaviour is relatively common due to the hormonal control of mother-pup interactions. Mothers with stronger hormonal bonds to a pup are more likely to successfully wean offspring (we’ve seen in previous blogs the risks to pups who wander, or whose mothers don’t pay enough attention to them!). It is possible that this hormonal control can sometimes ‘go wrong’ resulting in the evolutionary investment in an unrelated pup. This enhancement of mother-pup interaction could be evident under the conditions that; the advantage of the mother-pup bond enhancement is greater than detrimental effect of infrequent misdirected maternal investment over the mother’s lifetime. It could become permanently fixed in a population if the mother pup bond equates to a mean increase in fecundity over an individual’s lifespan. Put simply, forming a firm mother-pup bond is so critical on a busy seal breeding colony that this hormonal mechanism is highly selected. And sometimes that ‘need’ to bond can end up being misdirected, as in the foster mother here. For 6J, that same hormonal drive is probably what kept her on the colony battling for her pup!
After over a week of intense competition over the pup, 6J finally stopped returning to fight, leaving the pup in the care of its new foster mother. It is currently a large stage three pup, seemingly unscathed by the repeated conflicts, with as good a chance as any of surviving until adulthood.
Interestingly, it seems the initial confusion over whose pup it was, was created by another dry breeding season – basically when the pup was very young, 6J spent too long cooling down in OJ’s pool, and not being beside her pup – that gave the foster mother the chance to usurp the maternal role!
Above images shows ‘OJ’s’ pool on the 28th of October (left) and on the 18th of November (right)
Much more detail on the role of the hormone oxytocin in driving social bonds in seals , including mother-pup bonds, can be found on Dr Kelly Robinson’s web pages, and her her scientific publications from her PhD studies.