Even Earth’s mighty creatures are crumpling in numbers from the pressures humans are placing on them. Elephants may rise to the top in size but being corralled into captivity takes a toll on their ability to bear calves. In some instances, these lingering effects can last for decades and trickle down to their young.

Around 16,000 Asian elephants live in captivity at any one time in regions such as Myanmar, India, and Thailand. Those taken from the wild are used for a variety of functions, from hauling tree trunks and as tourism attractions to aiding conservation and research. 

Yet a team from the University of Sheffield in the UK found that the stress of such an altered way of life dramatically drops the reproduction rates of wild-caught female Asian elephants (Elephas maximus) used in the timber industry in Myanmar.

Of the 2,685 elephants studied in Proceedings of the Royal Society B, half were wild-caught elephants and the other half were born-and-raised in captivity. Both groups worked in the same environment and are governed by the same regulations, which is closely monitored by the government. Between 1911 and 1982, an estimated 17,000 elephants in Myanmar were captured. Such practices were banned in the 1990s, although it still happens on a small-scale or via illegal capture. 

"All captured elephants undergo an initial taming or ‘breaking’ procedure immediately after capture that lasts 4-12 weeks, depending on the temperament of each elephant," write the authors. "Older elephants generally require a longer period of taming than animals caught from the wild at younger ages or captive-born individuals, which are tamed using similar methods."

"The taming undoubtedly incorporates stress and compromises welfare, especially during the first few days. Elephants commonly resist training and reject food/water for the first few days, but are referred to as ‘broken’ when they begin to accept food, water, and human contact later in taming. Captive-born elephants are also tamed around the age of 4-5, but their training is thought to be easier and less stressful."

Wild-caught elephants were 28 percent less likely to reproduce than captive-born elephants. Not only that but females that were captured later in life were significantly less likely to reproduce overall.

When it came to the age of first reproduction, wild-caught elephants again displayed less biological fitness, being 65 percent less likely to give birth. Their age of first reproduction was pushed back by about 2 years on average. Oddly enough, the reverse was true for old-aged elephants: wild-caught females between 45 to 64 years of age were 63 percent and 95 percent more likely to reproduce than their captive-born peers, respectively. 

"We think that the stress imposed by the capture of elephants, which can negatively influence a whole host of processes in the animal such as the development of the fetus, body condition, and social interactions, is the key reason we see such big reductions in reproduction,” said co-lead author Mirkka Lahdenperä.

The team note that conservation programs with captive breeding should deeply consider whether taking individuals from the wild aids or hinders future conservation efforts.

"In elephants, although capture might be inevitable sometimes (e.g. for conservation, veterinary and anti-poaching purposes), consistent large-scale wild capture should be avoided to supplement captive populations because it fails to provide a sustainable long-term strategy and may have far-reaching evolutionary consequences for captive populations," the team conclude.