Photograph by Michael Nichols, Nat Geo Image Collection
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Female elephants thwart a male attempting to mate with a small female in Kenya's Samburu National Reserve.

Photograph by Michael Nichols, Nat Geo Image Collection

Elderly male elephants are the most determined to mate

The discovery could have implications for trophy hunters, who target the biggest and oldest bulls.

Measuring 10 feet tall at the shoulder and weighing over 6 tons, Matt the African savanna elephant is one of the largest land animals on Earth. And though the pachyderm is as old as 52, he still puts an incredible amount of energy into mating.

In fact, elderly males like Matt invest much more effort in tracking down and mating with females than do younger male elephants, according to a new study.

For about three months a year, Matt—who lives in a population that spans Kenya’s Samburu and Buffalo Springs National Reserves—goes into reproductive overdrive, a state biologists call musth (pronounced “must.”) During musth, middle-aged and elderly male elephants roam the savanna—spending little time eating or resting—to mate with as many females as they can. Females live in matriarchal groups, and males tend to live in separate groups until going into musth. (See stunning pictures of elephants.)

“Musth males are like testosterone machines,” says Lucy Taylor, a postdoctoral researcher at the University of Oxford who coauthored a new study on the phenomenon. They constantly drip strong-smelling urine, and specialized glands on their cheeks swell and ooze a thick liquid that contains pheromones.

And it works: “Musth males have a tremendous advantage over non-musth males,” according to Cynthia Moss, founder and director of the Amboseli Trust for Elephants.

Males in musth are so attractive to females that almost 80 percent of calves in the same population are sired by them, according to a 2007 study.

Even though males can begin mating around age 15, they don’t fall into a regular musth rhythm until they’re about 35. And by age 50, they’re rarin’ to go—an unusual timeline for most mammal species, whose reproduction tends to slow with age.

The discovery isn’t just fascinating: It could have major implications for the conservation of the species, which is listed as vulnerable by the International Union for Conservation of Nature. Ivory poachers and big game hunters frequently target big, old bulls, and it’s unclear how removing these reproductively active males from the population will impact the mammals' populations, the authors say. (Read: Under poaching pressure, elephants are evolving to lose their tusks.)

"It's well known that bull elephants become more successful in the mating game as they age, but this study shows for the first time we can see just how much of their available energy they put into making this happen," Frank Pope, CEO of Save the Elephants, says by email. "There may be lessons here for aging human males!”

An extra boost

To track the energy musth males were putting into mating, researchers fit GPS tracking collars on 30 adult bulls of various ages in a study population of about 900 individuals spanning the two national reserves in northern Kenya. The team logged the animals' movements intermittently between 2000 and 2018, tracking their average daily speed to represent the effort put into searching for females.

The oldest bulls were the slowest walkers in the study when they were out of musth, but old-timers kicked it into high gear when musth began, and they walked faster than their younger competitors. These 50-somethings also patrolled territories 350 percent larger.

“They’re basically conserving all of their energy and then expending it when they go into musth,” says Taylor, whose study was published recently in the Journal of Animal Ecology.

Why would older males focus so much on mating? First, since these elephants live into their 70s, females use age as a proxy for fitness as they seek out mates, Moss said.

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Another factor is “as they grow, the bulls get bigger and bigger and bigger. They get more dominant, and females prefer them,” Taylor said.

But even the biggest bulls need an extra boost.

“A male still needs to be able to see off his rivals, and musth gives that extra advantage to him when he’s competing for females,” Moss said.

Poaching impacts

By simply going into musth, a male is advertising to potential mates that he’s lived long enough to do so, Moss says—an impressive feat considering threats such as injuries, drought, and illness. But one thing they haven’t evolved to contend with is hunting, both illegal and legal.

Some of the older bulls Taylor’s team had been tracking for her study, for instance, were killed for their ivory in a rash of poaching in 2011. (Read about elephants poached in Africa’s “last safe haven.”)

“With the absence of these big dominant males, it’s going to be interesting to see how elephant reproduction changes,” Taylor says. “Is it going to change their reproductive strategies?”

Researchers don’t know, but she notes it’s within the power of citizens and governments to keep them from having to figure it out.

According to a study published in May, the elephant mortality rate from poaching is declining in response to lower demand for ivory on the international market, among other factors.

Regulatory measures, such as Hong Kong’s commitment to close its ivory market by 2021, might also help speed the decline in poaching.