Neuroscientist David Linden says they like to get high.
Animals in the wild will also voluntarily and repeatedly consume psychoactive plants and fungi. Birds, elephants, and monkeys have all been reported to enthusiastically seek out fruits and berries that have fallen to the ground and undergone natural fermentation to produce alcohol. In Gabon, which lies in the western equatorial region of Africa, boars, elephants, porcupines, and gorillas have all been reported to consume the intoxicating, hallucinogenic iboga plant (Tabernanthe iboga). There is even some evidence that young elephants learn to eat iboga from observing the actions of their elders in the social group. In the highlands of Ethiopia, goats cut the middleman out of the Starbucks business model by munching wild coffee berries and catching a caffeine buzz.
But do we really know whether these animals like the psychoactive effects of the drug, or are they just willing to put up with them as a side effect of consuming a valuable food source? After all, fermented fruit is a tasty and nutritious meal. While it’s hard to dissociate these motivations in animals, many cases suggest that the psychoactive effect is the primary motivator for consumption. Often, only a tiny amount of plant or fungus is consumed, so while its nutritional effect is minuscule its psychoactive effect is large
Perhaps the most dramatic example of nonnutritive animal intoxication is found among domesticated reindeer. The Chuckchee people of Siberia, who are reindeer herders, consume the bright red hallucinogenic mushroom Amanita muscaria as a ritual sacrament. Their reindeer also indulge. Having discovered the mushrooms growing wild under the birch trees, they gobble them up and then stagger around in a disoriented state, twitching their heads repeatedly as they wander off from the rest of the herd for hours at a time.