TURKU, Finland — Elephants benefit from having older siblings, especially sisters, new researcher reveals. Researchers studying semi-captive Asian elephants in Myanmar have found that calves benefit from having older sisters more than from having older brothers.
Oxford University researchers, along with colleagues in Myanmar and Finland, discovered that Asian elephants influence their younger siblings from early life to old age. Calves raised with older siblings have increased long-term survival compared to calves that do not have siblings. The study also revealed that elder sisters have a bigger impact than elder brothers.
Big sisters more beneficial to a long life than big brothers?
Female elephants raised with older sisters had higher long-term survival rates and reproduced for the first time an average of two years earlier compared to those raised with older brothers. Reproducing at an earlier age is usually leads to more offspring over the course of an elephant’s lifetime.
Male elephants raised with older sisters had a lower survival rate, but higher body weight compared to those raised with older brothers. Researchers say that seemingly detrimental effect may be due to the “live fast, die young” strategy, where the positive early increase in body mass could lead to survival costs later in life.
“Our research confirms that sibling relationships shape individual lives, particularly in social species, such as the elephants, where cooperative behaviors are essential to the development, survival and reproductive potential of individuals,” says study lead author Dr. Vérane Berger of the University of Turku in Finland in a media release.
Dr. Berger adds that the long-term consequences of sibling effects are understudied in long-lived animals, one of the reasons being that the logistic challenges of field studies make it hard to investigate effects over an animal’s entire lifespan. For the new study, the team was able to overcome that barrier by studying a population of government-owned, semi-captive timber elephants in Myanmar for which extensive records are kept.
Do other elephants behave this way?
The researchers analyzed precise reproductive and longevity information for 2,344 calves born between 1945 and 2018. The elephants are used during the day as riding, transport, and draft animals. At night, the elephants live unsupervised in forests and can interact and mate with both wild and tame elephants. Calves are raised by their mothers until the age of five, when humans begin training them for work. The Myanmar Timber Enterprise (MTE) imposes regulations on the daily and annual workload of elephants.
“Because the elephants live in their natural habitats, there are many similarities to wild elephants, such as natural foraging and no assistance in breeding. While there are differences – in the wild, family groups are probably bigger – there are more similarities than differences and we could assume that some of the associations found in our study would also hold true for wild elephants. But of course, these should be studied” says study co-author Dr. Mirkka Lahdenperä.
“By collecting more information on the body mass of mothers at birth, we hope to disentangle 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 on the effects siblings have on specific aspects of a younger calf’s health, such as immunity, muscular function and hormonal variations,” Dr. Berger concludes. “We could also investigate the influence of the sex and presence of younger calves on elder calf life history trajectory.”
The findings appear in the British Ecological Society’s Journal of Animal Ecology.
South West News Service writer Stephen Beech contributed to this report.