Ed Yong,”Razzle Dazzle ’Em.” ©2014
This passage is adapted from Ed Yong,”Razzle Dazzle ’Em.”
©2014 by Reed Business Information Ltd.
In 1909, the prevailing belief was that animals hid
themselves by matching their surroundings. Then
the painter and naturalist Abbott Handerson Thayer
suggested a different mechanism was at work: highly
conspicuous markings, such as the zebra’s stripes and
the oystercatcher’s black-and-white plumage, are
actually disguises. Predators, he reasoned, locate
their prey by looking for their outlines, so animals
with high-contrast markings that disrupt telltale
edges and create false ones can evade detection.
With this and other ideas about animal markings,
Thayer earned himself the title “father of
camouflage”. But although disruptive camouflage
was cited in countless textbooks, it remained largely
untested until 2005, when Innes Cuthill, Martin
Stevens and their colleagues at the University of
Bristol, United Kingdom, devised an experiment
using fake moths made from paper triangles. By
pinning them to oak trees, the researchers found that
“moths” with black markings on their edges were less
likely to be attacked by birds than those with central
markings or uniform colors. “It showed that
disruption was indeed a very good way of being
hidden,” says Stevens, now at the University of
Exeter, United Kingdom. Using a similar approach,
he and Cuthill later discovered that high-contrast
markings become less effective once their contrast
exceeds that in the creatures’ natural environment.
One way to avoid this is for some parts of the body to
blend in while others stand out.
Cuthill and Stevens revived interest in disruptive
camouflage, but the first real insights into just how
it works came only last year. Richard Webster at
Carleton University in Ottawa, Canada, asked
volunteers to search for virtual moths on a computer
screen while an eye-tracker monitored their gaze.
“We could almost get inside people’s eyes,” he says.
He found that the more patches moths had on their
edges, the more often volunteers failed to notice
them, and they needed to fixate their gaze on
Them for longer to have any chance of spotting them.
The eye-tracking vindicated Thayer again: by
breaking up an animal’s outline, disruptive
camouflage does impair a predator’s ability to spot its
prey
Although instructive, the experiment had an
obvious shortcoming: humans do not prey on moths,
let alone computer-generated ones. To test whether
disruptive colouring fools its intended audience,
Stevens has started field trials. In Zambia and South
Africa, his team is studying ground-nesting birds that
rely on disruptive camouflage, including nightjars
and plovers. His team measures the patterns on the
birds’ feathers to quantify how well hidden they are
in their environment. They also track the birds’
survival to determine how effectively they evade
predators.
Nightjars and plovers are difficult to spot in the
first place, so the researchers have employed sharp-
sighted local guides to help find them. This raises the
question of whether predators, like the guides, might
be less easily fooled by disruptive markings as they
become more familiar with them. Last year, Stevens
and his team found that people do gradually get
better at spotting virtual moths, especially if they see
several at the same time. He suspects that the
volunteers learn to stop the futile search for outlines,
and instead start scanning for the high-contrast
markings.
Whether non-human predators adopt the same
tactic is hard to say. They may not even see
camouflage markings in the same way that we do.
But if predators can learn to see through disruptive
camouflage, it would suggest that this concealment
strategy is more likely to evolve in prey that face
short-lived or generalist predators than long-lived or
specialist ones.
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