Many animals use the colours and patterns on their bodies to help them blend into the background and avoid the attention of predators. But this strategy, crypsis, is far from perfect. As soon as the animal moves, the camouflage is broken, and it is much easier for a predator to see and catch it. So how do animals protect themselves when they’re on the move?
Researchers are exploring whether high-contrast patterns during motion, such as stripes and zigzags, may be distorting the predator’s perception of where the animal is going. But, as little is known about such “motion dazzle”, we have built an online game to help shed light on it.
Lessons From War
The idea is that it may be more effective for animals to focus on preventing capture, rather then preventing detection or recognition, is actually more than 100 years old. It was naturalist Abbott Thayer who suggested that high-contrast patterns may distort the perceived speed or direction of a moving object, making it harder to track and capture.
Such motion dazzle patterns were actually used in World War I and II, where some ships were painted with black and white geometric patterns in an attempt to reduce the number of successful torpedo attacks from submarines. However, due to many other factors affecting wartime naval losses, it is unclear whether motion dazzle patterns actually had the desired effect.
HMS Argus displaying a coat of dazzle camouflage in 1918. wikimedia
What about the natural world? Zebras have bold stripes, and scientists have debated the function of their patterns since Darwin’s time. A recent modelling study suggested that when zebras move, their stripes create contradictory signals about their direction of movement that is likely to confuse predators. There are potentially two visual illusions responsible for this, which could form the basis of motion dazzle effects: the wagon wheel effect and the barber pole illusion.
The wagon wheel effect is named after Western movies, where the wheels on wagons often appear to be moving backwards. This is because the visual system takes “snapshots” over time and links them to create a continuous scene, in the same manner as recording film. If a wheel spoke moves forward rapidly between sampling events, it will appear to have moved backwards as it will be misidentified as the following spoke.
Wagon Wheel effect explained.
The barber pole illusion (also known as the aperture effect) occurs because the moving stripes provide ambiguous information about the true direction of movement. These illusory effects produced by stripes could therefore lead to difficulties in judging the speed and movement of a moving target. However, the zebra study was entirely theoretical and didn’t test whether striped patterns actually affected the judgements of real observers.
Surprisingly, the first experimental tests of the effectiveness of motion dazzle patterns weren’t carried out until recently. Some studies have shown that strikingly patterned targets can be more difficult to catch than targets with other patterns in studies using humans as “predators” playing touch screen computer games. However, other studies have found no clear advantage for motion dazzle patterns So although patterns can affect our perception of movement, it’s still not clear which are most effective at doing so.
Can you see the spider? Crypsis can be pretty effective - as long as you don’t move. J Kelley, Author provided
We are addressing the question of which patterns are best for avoiding predators during movement using Dazzle Bug – an online game that asks players to imagine themselves as a predator, trying to catch a moving bug as fast as possible. Each bug has a different body pattern as well as a random pattern of movement. Bugs with easy to catch patterns will disappear, whereas those that are particularly tricky to catch will survive ––just like in nature. Over time, the patterns on the bugs' body will evolve so that they become harder to catch with each successive generation.
This citizen science project will allow us to see what patterns are most effective at evading capture. We can then use these results to look at what visual effects these patterns have, and to see whether these patterns match up with those found on real animals in the wild.
Our findings will offer insight into the role of stripes, which are common in many species. While these patterns may have evolved to confuse the visual perception of a predator, they may also be a result of other selection pressures, such as attracting a mate or regulating body temperature. If striped patterns survive and evolve in the game, this would provide strong evidence that these patterns do act to confuse human predators, perhaps by producing the illusions described above. As motion perception seems to be highly conserved across a wide range of populations, these illusions may occur for many other predators too.
If we find that patterns other than stripes – such as speckles, splotches or zigzags – are most effective in preventing capture, this then leads to new and interesting questions about how these patterns may act to confuse or mislead. Whatever the outcome, Dazzle Bug will provide insight into how bodily patterns may have evolved to help animals to survive life on the go.