“Hey, Baby! I’m Feeling Great!” *cough cough* “Really!”
For the first half of the above video, a sick male zebra finch sits quietly on the floor of his cage. He’s not feeling so great, trying to rest and keep quiet while his immune system is in hyperdrive. But half an hour later, shown in the second half of the video, an unfamiliar female has entered the cage. To the male bird, that changes everything. He hops around with excitement and interest as if he didn’t feel sick at all.
Behavioral biologist Patricia Lopes of the University of California, Berkeley, and her colleagues injected this finch and others with bits of E. coli bacteria — triggering their immune systems without actually infecting them. They watched the birds as they lay sick, then compared how it behaved when a female was thrust into the picture, counting its hops and the time it spent resting. They found the male birds’ behavior changed completely, acting as if they weren’t sick in an effort to court the female.