When under severe stress, they projectile vomit their partially digested carrion meals all over an intruder. In a bizarre twist of fate, these birds have an excellent sense of smell that helps them locate rotting flesh. Other species reach behind to grab the feces with their mandibles, or mouthparts, and fling it yonder. Lee Dyer and Grant Gentry, biologists at Mesa State College in Colorado, have documented this behavior in hundreds of tropical caterpillars. According to Dyer and Gentry, this grody behavior likely evolved to prevent parasites from finding the caterpillars.
Parasites locate nice juicy caterpillars to lay eggs on by smelling for caterpillar feces.
But if a caterpillar flings or squirts its poop as far away as possible, parasites have a harder time finding them.