If you’ve ever felt held back in your life by an older brother, a new study shows that humans aren’t the only ones.
Today, scientists report that elephants benefit more from having older sisters than older brothers when they’re growing up.
Scientists studied populations of semi-captive Asian elephants (Elephas maximus) in Myanmar in Southeast Asia.
They found that female calves raised with older sisters lived longer and reproduced two years earlier than those with older brothers, although it was unclear why.
Overall, Asian elephant siblings influence their offspring from an early age, when they are young, until the end of their lives, the researchers claim.
Experts found that raising calves with an older sibling increased the long-term survival of calves compared with no siblings, but older sisters had a bigger impact than older brothers in this respect.
The study was carried out by researchers at universities in Finland, the UK and Myanmar and published in the British Ecological Society’s Journal of Animal Ecology.
Lead author Dr Vérane Berger at the University of Turku, Finland, said: ‘Our study confirms that sibling relationships shape individual lives, especially in social species, such as elephants, where cooperative behaviours are necessary for the growth, survival and reproductive potential of individuals.”
The researchers used a large, multi-generational, government-owned, semi-captive dataset of Asian elephants to examine the effects of older siblings’ presence and sex on the body mass, weight, reproduction, sex and survival of the next calf.
The records contained reproductive and longevity information for 2,344 calves born between 1945 and 2018.
In female elephants, those raised with older sisters were more likely to survive longer and give birth for the first time an average of two years earlier, compared to those with older brothers.
Reproduction at an earlier age usually involves more offspring throughout the elephant’s lifetime.
In male elephants, those raised with sisters had lower survival rates but higher body weights than those with older brothers.
For males with older sisters, it is possible that a positive early increase in body mass could lead to survival costs later in life.
Because the study is correlated, the influence of external factors outside of sibling influence, such as quality of maternal care, workload and elephant management, cannot be excluded.
Dr Berger said: “By gathering more information about mothers’ body mass at birth, we hope to remove maternal effects from sibling effects.
‘More data will also let us explore the effects of the environment on sibling relationships and go into more detail about the impact of siblings on specific aspects of their younger calf’s health, such as immunity, muscular function and hormonal variations.
‘We were also able to investigate the influence of sex and presence of younger calves on the historical trajectories of adult calves.’
The study was carried out on government-owned Myanmar wooden elephants living in forest camps, distributed across the country and considered ‘semi-captive.’
Elephants are used during the day as riding, transporting and drafting animals. They live unattended in the forest at night and can interact and mate with both wild and domesticated elephants.
Calves are raised by their mothers until the age of five, when they are trained to work. The Myanmar Timber Enterprise (MTE) imposes regulations on the daily and annual workload of elephants.
Unfortunately, the Asian elephant is classified as endangered on the IUCN Red List of Threatened Species.
According to the Zoological Society of London (ZSL), it is under increasing pressure in the wild due to habitat destruction through human population growth.
As the human population continues to grow, elephants have less space to live naturally and are forced into smaller areas and more conflicting events with humans.
The African savanna elephant (Loxodonta africana) is also being driven to near extinction due to hunting and is now listed as ‘vulnerable’ in the IUCN Red List.