Some grey seal mums adopt risky tactics when it comes to the future of their young, a strategy that can give their pup a real advantage, according to scientists.
Researchers from the Sea Mammal Research Unit (SMRU) at the University of St Andrews, and Durham University, looking at grey seal colonies in Scotland, found that some seal mothers are flexible in the parenting style they adopt and ‘gamble’ on the outcome of their actions, whilst others play it safe and steady.
The study is the first to demonstrate how variation in personality traits in large marine mammals in the wild can persist, rather than a single, successful, personality type dominating the population.
The research shows that some seal mothers have a very fixed approach to looking after their pups, and tend to behave in a similar fashion whatever the local conditions on the breeding colony are, whether they are in a crowded and busy location, or in a less disturbed situation.
These mums tend to achieve average success in terms of their pups’ weight gain (crucial to the future survival of the pup), so that, by-and-large, they generally do well using a ‘play it safe’ approach to life.
Other seal mothers have a very different approach. These mums are more flexible and try to adjust their mothering behaviour according to the local conditions. In potentially unpredictable situations, this can be risky; sometimes they get it right and their pups fare very well, but other times they might get it wrong and their pups do rather badly.
The findings, published in the journal PLoS One, show that individual animals can differ markedly in their ability to adjust their behaviour to their local environmental conditions and that large variations in behavioural strategies can persist within a species.
According to the researchers, the results for both extremes of personality show how different types can be maintained by selection. This retains behavioural diversity within a species, potentially making the species more resilient to environmental change.
The results are relevant to environment and conservation policies that use a one-size-fits-all approach, as these may need to be re-evaluated to take into account individual differences in animal personality, the researchers say.
Co-author Dr Paddy Pomeroy, of the Sea Mammal Research Unit at the University of St Andrews, said: “This is the first time we've been able to link behavioural types and individual measures of reproductive success and the results are surprising.
“If more flexible mothers are better and worse pup rearers, we need to understand how breeding "successes" and "failures" are apportioned over lifetimes. Our long term studies of individuals are invaluable for this.”
Lead author, Dr Sean Twiss, School of Biological and Biomedical Sciences, Durham University, said: “Some mums have a very fixed way of caring for their pups, come what may, whilst others are more flexible.
“Seals that ‘gamble’ and try to fit their behaviour to their immediate surroundings can do very well, if they get it right! However, being flexible can be risky - a mum might ‘mis-judge’ the conditions and fail to match her behaviour to the prevailing conditions.
“In either resting or disturbed situations, seal mums behaved in very individual ways, some showing high levels of maternal attentiveness, others showing low levels. Some behaved the same when disturbed as they did at rest while other individuals changed their behaviour dramatically when disturbed.”
These differences in mothers’ behaviour, either fixed or flexible, can have profound effects on their pups. After about 2-3 weeks of being looked after by their mothers, all pups are left to fend for themselves, and have to teach themselves to feed. The fatter a mum leaves her pup, the more time the pup has to learn, and its chances of surviving are better.
The scientists observed seals on the Scottish island of North Rona during the breeding season over two years. The team observed seals in their natural habitat to analyse responses to unusual stimuli (disturbances) and to assess seal behaviour at rest.
The research has been part-funded by NERC’s Living With Environmental Change programme, a NERC grant and the Esmée Fairbairn Foundation.
How they did it
The researchers ran 30-minute observations on 14 females to see how they behaved at rest. The team measured the attentiveness of the mothers towards their pups during these periods by recording the number of pup checks made (where the mother raises her head off the ground and moves it in the direction of her young to check their well-being). Repeating these observations twice on each seal showed that mothers varied considerably, and consistently, in their behaviour, with some showing low levels of maternal attentiveness, whilst others checked their pups much more often.
The team then used a remote controlled vehicle (RCV) with a fitted video camera to test how seals reacted to mild disturbance, including approaches by the RCV and wolf calls played from the vehicle.
The seals varied in their responses to the RCV from almost completely ignoring its presence to pushing it with their muzzles. Again, mothers varied considerably in the number of pup checks they made during these disturbances.
The team also measured and weighed each seal mum and pup before and after each test and observation. Comparing these measurements for the behaviourally ‘fixed’ and ‘flexible’ seals, the team found an intriguing pattern: All mums with the ‘fixed’ approach had very average pup growth rates, while some of the ‘flexible’ mums did really well, with their pups growing at twice the rate of others, but the rest did rather poorly, with pup growth rates well below average.
The researchers can identify individual seals using their unique and varied patterns on their fur and this allows them to observe maternal behaviour over multiple years as seals generally return to the same site to breed.