Chances are you've tried to hide a runny nose and cough when you're sick at the office or around family members, and a new study finds animals do something similar.
Some animals — including song sparrows, zebra finches, monkeys and rats — will hide symptoms of sickness and act as if they are healthy in certain social situations. Specifically, they'll do so when they have an opportunity to mate, when their children are around or when they are housed with a large herd, according to a new study, which reviewed more than 70 past studies on animal behavior.
When humans and animals fall ill, they typically exhibit a range of so-called "sickness behaviors": They may eat and drink less, move less, sleep more, and feel a decreased desire to socialize, explore or have sex. By conserving energy on what's considered non-essential activities, like pleasurable sex, the animal's body can focus on healing its immune system, some scientists hypothesize. [The 12 Weirdest Animal Discoveries]
But the new review suggests animals don't always act this way: In one study, male zebra finches who had immune problems acted as if they were healthy when confronted with the stimulating possibility of sex with a female zebra finch. Despite being infected, the male zebra finches courted in the normal fashion.
In another study, zebra finches housed with many other birds exhibited fewer sickness behaviors, even though their immune systems showed signs of inflammation. Scientists observed the same phenomenon in male rats housed in groups.
Study researcher Patricia Lopes, a biologist at the University of Zurich in Switzerland, said that these social contexts may motivate animals to hide their sickness so they can maintain social status.
Researchers have thought "that behaving sick helps animals recover from the disease, and so this should be the default way to behave when sick," Lopes said in a press release. "However, if being sick coincides with, for example, a unique opportunity to mate, then animals may adjust their priorities and behave as though they are not sick."
The findings might help scientists better detect and control the growing number of animal-originated diseases. Researchers can now recognize that animals may act is if they are healthy when they are actually sick, Lopes told Live Science.
It's also possible that animals don't necessarily "fake" being healthy, but that they actually do feel better when around other animals, the researchers said.
This could have implications for improving the health of sick animals. "If housing animals together can improve the symptoms (such as pain) of diseases that cannot be transmitted (e.g., cancer), then we might be able to increase the well-being of captive animals suffering from disease," Lopes said in an email.
Future research will investigate whether changing the social context of sick animals, by housing them together, for example, will have a clear benefit or cost.