A study of semi-captive Asian elephants in Myanmar revealed that young elephants benefit from having older siblings, even more so if they are older sisters.
The new discovery was made by a research team with members from Finland, Myanmar, and the UK who have conducted the study finding that Asian elephant siblings affect and influence the family's younger offspring from early through late life stages. Growing up with older siblings shows a significant increase in the calves' long-term survival rates compared to those who were raised alone. Additionally, this effect was much more pronounced in elder sisters compared to elder brothers.
Researchers detail their study in the report "The elephant in the family: Costs and benefits of elder siblings on younger offspring life-history trajectory in a matrilineal mammal," appearing in the Journal of Animal Ecology.
TOPSHOT - This photo taken on August 3, 2019 shows forest rangers preparing to release the wild elephants into the Zarmaye nature reserve located in the Bago region. - Two wild elephants, which had been foraging villages and a highway for food in Yangon, were caught on August 3 and released into the Zarmaye nature reserve in the Bago region.
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The Impact of Having Older Siblings
Researchers found out that for female elephants, offspring raised with older sisters saw higher long-term survival rates. Also on average, those with older sisters reproduced for the first time two years earlier compared with those raised with older brothers. An earlier age of reproduction is generally associated with more offspring over the course of an elephant's lifetime.
In male elephants, the study showed that those raised with older sisters had less survival rates but had higher average body weight compared to those who grew up with older brothers. This seemingly detrimental effect, according to the researchers, can be explained by a "live-fast, die young" strategy, where positive early increases in body mass could lead to survival costs in later stages.
"Our research confirms that sibling relationships shape individual lives, particularly in social species, such as the elephants, where cooperative behaviours are essential to the development, survival and reproductive potential of individuals," explains Dr. Vérane Berger from the University of Turku and lead author of the study.
The long-term consequences of sibling effects remain understudied in long-lived animals. Researchers explain that one of the reasons for this is that the logistic challenges of field studies make it difficult to examine effects over their entire lifespan.
Observing Semi-Captive Elephants in Myanmar
Researchers were able to work around these logistic challenges by working with government-owned, semi-captive timber elephants in Myanmar, where extensive life history records of these animals are also kept. These elephants are used in the day as transport and draft animals. At night, they are left unsupervised and allowed to interact and mate with both tame and wild elephants. Calves are raised by their mothers until they are five years old, and around the same time, they start training for work. The Myanmar Timber Enterprise (MTE) also imposes regulations on daily and annual elephant workloads.
"Because the elephants live in their natural habitats, there are many similarities to wild elephants, such as natural foraging and no assistance in breeding," says Dr. Mirkka Lahdenperä from the University of Turku and co-author of the study. She adds that while there are difference, such as the possibility of larger family groups in the wild, there are still more similiarities compared to differences. The findings in their study, therefore, might also be applicable for wild elephants, although she stresses the need for further studies.
Researchers used a large and multi-generational dataset of semi-captive Asian elephants to better understand the impact of the presence and sex of elder siblings on various factors such as body mass, reproduction, sex, and survival of the next offspring.
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