Is it true that elephants, monkeys, dolphins and other animals seek out recreational drugs in nature? Jason G Goldman investigates

In South Africa, local legend has it that the elephants like to get drunk. They seek out the marula tree, overindulge on its sweet fruits, and enjoy the intoxicating effects of the slightly fermented juice.

Tales of the tipsy pachyderms go back at least two centuries. In the 1830s, a French naturalist called Adulphe Delegorgue described stories from his Zulu guides of mysteriously aggressive behaviour in male elephants after they fed on the marula fruits. "The elephant has in common with man a predilection for a gentle warming of the brain induced by fruit which has been fermented by the action of the sun," wrote Delegorgue.

Elephants aren't the only critters accused of indulging in the occasional cocktail or dose of drugs. Tales are told of wallabies getting high on poppy plants in Australia or dogs reportedly becoming addicted to the toxic substance secreted by cane toads. And stories abound of vervet monkeys on the Carribean island of St. Kitts, sneakily imbibing the brightly coloured cocktails of distracted tourists.

But how much of this is the result of projecting our own fascination with mind-altering substances onto other animals? Decades of laboratory research has shown that we can easily induce addictive behaviour in animals by making addictive substances easily available to them. But do wild animals really get drunk or high?

Vervet monkeys are one species that researchers hoped could help answer this question. Sometimes called green monkeys, they are native to Africa, but a handful of isolated groups wound up scattered across islands in the Caribbean. In the 18th and 19th Centuries, slavers often took the monkeys as pets, and when their ships landed in the new world, the monkeys easily escaped or were intentionally released. There, free of most of their predators, the small primates adapted quite well to tropical island life. For 300 years, the animals lived in an environment dominated by sugar cane plantations. And when the sugar cane was burned, or occasionally fermented before harvest, it became a treat for the monkeys. As they became accustomed to the ethanol in the fermented cane juice, the monkeys may have developed both a taste and tolerance for alcohol. Local stories are told of catching wild monkeys by supplying them with a mixture of rum and molasses in hollowed out coconut shells. The drunk primates could then be captured without hassle.

Descendants of those introduced monkeys have since been studied so that we can understand more about their boozy behavior. One study found that nearly one in five monkeys preferred a cocktail of alcohol mixed with sugar water over a sip of sugar water alone.

Intriguingly, younger individuals were more likely to drink than older individuals, and most of the drinking was done by teenagers of both sexes. The researchers, led by Jorge Juarez of Universidad Nacional Autonoma de Mexico, suspect that older monkeys shun alcohol because of the stresses of monkey politics. "It is [possible] that adults drink less because they have to be more alert and perceptive of the social dynamics of the group." In other words, at some point the monkeys leave their days of heavy drinking and hangovers behind and start acting like adults.

The same can't necessarily be said for rough-toothed dolphins, though. The marine mammals look a bit like the more familiar bottlenose variety, but can be distinguished by white markings around the beak. In 1995, marine scientist Lisa Steiner provided perhaps the first description of a peculiar behaviour she witnessed near the Azores.

One evening, she motored by an aggregation of some 50-60 dolphins, each in its own group of four-to-seven individuals. The dolphins appeared to be feeding, but they were acting strange, not displaying the typical high-energy behaviour. A few were lazily feeding, but many were just slowly swimming about. That's when she noticed the puffer fish. "Four inflated puffer fish were seen with the dolphins and one of them, which was upside down, was being pushed around by one of the dolphins," writes Steiner. She suspected that the behaviour was some sort of play. "Towards the end of the encounter, several of the dolphins were observed lying motionless at the surface with their backs and the tops of their heads clearly visible."

It isn't necessarily clear just what the dolphins were doing with the puffer fish, but their uncharacteristically lackadaisical behaviour implies to some that they were experiencing some mild intoxication from puffer fish venom, tetrodotoxin. A BBC documentary called Dolphins: Spy in the Pod that aired last year made the same argument. It's a controversial idea, because tetrodotoxin is so dangerous that a small dose can kill.

Writing at Discover Magazine, marine biologist Christie Wilcox explains: "Milligram-for-milligram, tetrodotoxin is 120,000 times as deadly as cocaine, 40,000 times as deadly as meth, and more than 50 million times as deadly as THC. It is tens to hundreds of times more lethal than the venoms of the most notorious animals in the world including the widow spiders and the black mamba. It’s more potent than VX nerve gas, formaldehyde, or even ricin. It is, quite literally, one of the most toxic compounds known to man." She argues that curious, big-brained mammals, dolphins might explore puffer fish, and may accidentally expose themselves to a bit of the toxin, but is extremely sceptical of the notion that dolphins are dosing themselves intentionally, with such precision to achieve a bit of numbness without accidentally overdosing. In addition, tetrodotoxin isn't actually psychoactive. It induces numbness, but doesn't alter the mind, making it a poor choice of drug.

As for the elephants, the science is pretty clear. The animals are so massive that it would take a tremendous amount of the marula fruit to become intoxicated. Physiologists Steve Morris, David Humphreys, and Dan Reynolds of the University of Bristol first heard the rumours of the drunk elephants while in South Africa for a scientific conference, so they set about determining whether the legends might reflect some truth.

A search of the scientific literature supported the notion that elephants could at least become drunk. A 1984 study showed that they were happy to drink up a 7% alcohol solution, and several drank enough to alter their behaviour. While they didn't "act drunk", in human terms, they decreased the time spent feeding, drinking, bathing, and exploring, and became more lethargic. Several displayed behaviours that indicated they were uncomfortable, or perhaps slightly ill.

Drunk trunk?

But just because elephants can become intoxicated doesn't mean that they do it in the wild routinely enough to inspire all the marula tree legends. A 3,000kg (6,600lb) elephant would have to drink between 10 and 27 litres of a 7% alcohol solution in a relatively short amount of time to experience any overt behavioural changes. Even if marula fruit contained 3% ethanol (a generous estimate) an elephant eating only marula fruits at a normal pace would barely consume half the alcohol necessary in a single day to become drunk. If it wanted to get drunk, given the constraints of its anatomy and physiology, an elephant would have to eat marula fruit at 400% its normal feeding rate while also eschewing all additional water intake. "On our analysis," the researchers conclude, "this seems extremely unlikely."

Still, something must explain the unusual behaviour of elephants around marula trees. Morris, Humphreys, and Reynolds offer two possible explanations. First, their unusually aggressive behaviour may simply reflect the fruit's status as a highly prized food item. A second, more intriguing hypothesis, is that there's another intoxicant that they're consuming. In addition to the fruits, elephants also sometimes eat the tree’s bark. This often contains beetle pupae, which contain a substance that local Africans historically used to poison their arrow tips. If they were ingesting the beetle toxin, perhaps that could explain the unusual antics of the pachyderms.

It's a seductive idea, isn't it? That other animals are as interested in getting as drunk and high as we are? While there are a few legitimate accounts of wild animals intentionally seeking out mind-altering substances, most such tales are based on legend and hearsay, and others simply have insufficient evidence to understand. Morris, Humphreys, and Reynolds point out that the majority of drunken animal stories are "anecdotal, mired in folklore and myth". And in a few cases, it’s possible that people are mistakenly attributing certain movements or temperaments to how humans act when inebriated. Wild animal drunkenness may only exist in the (occasionally tipsy) eye of the beholder.

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