To hide in the wild, some animals adopt bold, contrasting patterns that would seem to make them stand out rather than blend in. The strategy works, and now scientists think they have figured out why: Such patterns break up the animals' outlines, making them harder to distinguish.
The most common trick in camouflage is to mimic habitat. The flounder, for example, looks just like the sandy seabed where it rests. But some animals, like the clownfish, seem to hide themselves by using bold colors. Taking such patterns as inspiration, armies have covered tanks and uniforms with similar patterns since WWI. The explanation--that such patterns thwart efforts to identify the outlines--has been in biology textbooks for decades. But the idea has never actually been field tested until now.
A team led by Innes Cuthill, a biologist at the University of Bristol, in the United Kingdom, pinned fake moths on the trunks of oak trees. They used dead meal worms for the bodies and paper triangles as wings. The wings were printed with either monochrome dark gray or tan patterns, or various splotch patterns of both. The team distributed the moths randomly throughout a forest and waited to see how long it took birds to swoop in for a free meal.
As expected, birds quickly spotted and ate moths that were all dark gray or all tan. Moths with dark gray splotches near the center of their wings did better at escaping notice. But the best pattern of camouflage was boldly contrasting splotches along the edge of the wings. Ninety percent of these moths survived the entire day, compared to 70% for their center-splotched counterparts. This shows that "disruption of the outline" is the key to good camouflage, the team reports in the 3 March issue of Nature.
It's a convincing study, says John Endler, a biologist at the University of California, Santa Barbara. "What is surprising," he says, "is that no one has bothered to do this before." Endler would next like to see whether disruptive camouflage has any advantage over camouflage that blends into the surroundings.