Richard Collins: Bold mothers seal the deal for pups
‘NOTHING ventured nothing gained” and “faint heart never won fair lady”. But, “fools rush in where angels fear to tread” and “discretion is the better part of valour”. So how adventurous is it wise to be? asks .
Some people are notorious risk-takers, others are wimps. Do animals have similar personality traits? Seal expert Christi Bubac, of the University of Alberta, thinks they do.
The grey seal is the largest wild creature most Irish people ever encounter. Its bones were unearthed from a 6,000-year-old kitchen midden, but a seal found in Cork in 1836 was the first to be recorded in modern times. The species has prospered since then; it’s now our commonest marine mammal.
Greys haul out at traditional sites, where all-round visibility allows them keep an eye out for danger. Up to a thousand greys frequent an Trá Bán on Great Blasket. There is safety in numbers; a crowd is intimidating. Many eyes and ears make it virtually impossible for an enemy to creep up undetected.
Females give birth at these rookeries and are mated immediately afterwards by bulls competing for their favours.
Although beautifully adapted to living in the sea, these huge legless mammals crawl about clumsily on land. Minimising the risk from predators, mothers get through the nursing period a quickly as possible. A baby seal is suckled on extremely rich milk for two to three weeks, by which time it’s three times heavier than it was at birth. Then the mother deserts her calf, leaving it to fend for itself and go to sea unaided.
The parent’s behaviour, during the short lactation period, is crucial to her calf’s prospects. Facing a perceived threat, a mother must decide whether to flee or stand her ground. Making a dash for the sea may leave hers calf undefended, vulnerable to being crushed by stampeding adults, but facing down a potential enemy could threaten both her own and her calf’s lives.
The rookeries on Nova Scotia’s Sable Island are the largest in the world; 424,000 grey seals were counted there in 2016. Over an eight year period, Bubac studied the responses of 469 Sable Island females to being approached by observers. Each animal was given a “boldness” score. To help estimate the possible effects of this maternal behaviour on a calf’s development, the weights of babies were recorded.
The research showed that a boldness disposition was “highly repeatable between and within years”. Leopards don’t change their spots. Neither, it seems, do seals in their responses to danger. The tendency to stand or retreat in the face of a perceived threat, seems to be innate, an aspect of an individual’s personality. Like their human counterparts, a seal tends to be either brave or cautious. Older mothers were bolder than younger ones. Evidently, a seal’s behaviour is tempered by experience.
Significantly, pups whose mothers had bold personalities were 2kg heavier, on average, than those born to their more timid cousins. The heavier a pup is, when facing out to sea for the first time, the better its chances of survival. Having a brave mother, therefore, ensures a better start in life.
But boldness is just one personality trait; there must be many others. These findings, the researchers say, suggest that “individual differences in behaviour influence various aspects of ecology including species interactions, species distributions and life history strategies”.
But if being bold is such a successful trait, why are some mothers shy?
