A sleep-deprived panda inadvertently crushed her newborn cub to death at a zoo in China last week. "Pandas who lose their young tend to be depressed for a month or so," said a zoo official. "Yaya appeared to be so sad when she couldn't find her baby. … Tears could be seen in her eyes." What happens when a zoo animal gets depressed?
It gets special treats or psychiatric treatment. Keepers can tell something's wrong when an animal becomes lethargic and unresponsive or stops eating its food. Other warning signs include excessive grooming (like picking fur or plucking feathers), rocking in place, and pacing in circles. Zoo employees must first rule out physical ailments that could cause similar symptoms. An animal with an ulcer or a broken finger, for example, might mope around in the corner because it's in pain. A skin condition might elicit a grooming response that looks something like OCD.
A sad-sack animal can sometimes be coaxed out of a funk with "enrichment items" like toys and special foods. The pandas at the National Zoo get "fruitsicles"—apple-juice-flavored ices with embedded pieces of fruit. A blue period may also pass on its own, given enough time.
Some zoo veterinarians prescribe antidepressants as a last resort. Last year, the Toledo Zoo admitted that it had been running an extensive psychiatric program: One gorilla took Prozac for anxiety that seemed to be associated with her menstrual cycle, zebras and wildebeests were given the antipsychotic Haldol to relax in a new environment, and an agitated tiger was dosed with Valium.
It's not clear how well these drugs work for exotic animals—there aren't many placebo-controlled studies of antidepressant use in gorillas, zebras, and tigers. We've got more information on dogs and cats: Both SSRI-class drugs (like Prozac) and tricyclics (like Anafranil) seem to work. Researchers assess a pet's anxiety by counting anxious behaviors, like the number of times it urinates in a stressful situation.
When veterinarians dole out antidepressants, they almost always go off-label. That means they're prescribing a drug that's only been approved for human use. (This is perfectly legal.) The Food and Drug Administration has approved only one antidepressant for animal use—Clomicalm, which is the same drug as Anafranil. But the approval extends only to dogs, and only to treat "separation anxiety." Studies reveal that training an anxious dog works just as well as giving it Clomicalm, but it takes a lot longer.
Bonus Explainer: Are antidepressants tested on animals as they're developed? Yes. Drug companies use animals to check both the safety and the efficacy of new compounds. Antidepressants are deemed effective if they extend the amount of time an animal—like a mouse—is willing to endure unpleasant situations—like swimming in a pool of water. No one knows if this really corresponds to the animal's "happiness," but researchers have found that it correlates with drug efficacy in humans. As the president of R&D at Wyeth explained to the New York Times a few years ago, "[W]e don't try to relate the behavior in an animal to a human behavior."
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Explainer thanks Melissa Bain of the University of California and William Xanten of the National Zoo.