When is camouflage concealing

Biologists that study animal colouration have the formidable task of demonstrating how animals’ colouration works. The drab lizard camouflages to its grassy surroundings. The iridescent poison dart frog advertises its unpalatability. And stripey zebras disorientates predators as they strike.

It is easy to say that, just because an animal looks camouflaged to its environment, it IS camouflaged. For those that are curious, this isn’t sufficient!? One must first rule out possible alternative explanations. For instance, could the dark colour of the lizard help regulate temperature instead of contributing to concealment, is the bright colours of the poison dart frog cryptic to the eyes of its predators, and is it even possible for a colouration to disorient a pouncing predator.

A classic example of miss classifying an animals coloration was made by the father of animal camouflage, Abbott Thayer. Thayer suggested the–now comical–idea that flamingos are camouflaged: “These various sketches of Flamingoes … show how wonderfully such birds match or reproduce the colors of morning or evening skies to the eyes of the inhabitants of the water… Commonly, the bird’s upper outline ‘melts’ into the sky, leaving the rest of his contour, seen through the water, agitated and muddied by this feet, to be lost in the indeterminate color-mass of the flock.”

camouflage flamingo

This just-so stories of animal camouflage is a warning; to claim an animals colorations functions as camouflage, one needs to test that camouflage’s function.

This Rule 101 of classifying animal colouration persists, not just for diagnosing camouflage, but also for specifying the specific camouflage. To distinguish between whether a camouflage pattern provides reduced detectability (background matching) or impairs recognition (disruptive coloration).

Disruptive camouflage and its effect on object recognition

Whether hiding from Lions on the Serengeti or dodging bullets on the battlefield, avoiding unwanted eyes should be high up on your priorities!

In nature, animals have evolved different strategies to achieve concealment. By resembling the appearance of its surroundings (“background matching”) an individual can reduce its chance of being detected. However, background matching has its limitations since many potential prey have characteristic features, such as edges, that predators can employ in the detection process. A 100-year old theory speculated that background matching camouflage can benefit from a complementary camouflage strategy of using highly contrasting patterns to disrupt the ability of predators to detect these characteristic features.

Disruptive markings are widely thought to obscure animals’ outlines and breakup their edges, making boundary and overall shape less recognisable to would-be predators. Whilst many animals, such as zebras, tigers and cuttlefish, have been proposed to have disruptive camouflage—not to mention a host of military uniforms and equipment—to date there is no evidence show that objects with disruptive patterns are actually harder to recognise once encountered, a key prediction of this concept.

Here at Carleton University, Ottawa, Canada, we set out to test experimentally if disruptive camouflage truly misleads humans when searching for animals. Using humans hunting on computer screens (Fig. 1a) we looked at the survivorship of artificial moth targets with varying numbers of edge patches. Further, we used eye tracking technology to measure target recognisability (Fig. 1b). Targets that were looked at for longer were assumed to be harder to recognise.
It was predicted that if number of edge patches improves camouflage by disruptive coloration, then target moths with more edge intersecting patches should have a high survivorship due to impaired recognition.

Fig 1 a) Photograph of a human subject hunting on a computer screen for an moth hidden (see grey arrow) on the tree image, b) a close up of the eye-tracking apparatus and the screen with an overlay showing where the subject was looking during their search.

Indeed, we found that targets with more edge intersecting patches took longer to be discovered. This cannot be explained due to background matching alone because this was even the case for edge markings that were dissimilar from the background. Crucially, targets with more edge patches took longer to be recognised and were overlooked more often.

Through this novel use of eye-tracking technology, the study provides key evidence to support the hypothesis that disruptive coloration can achieve camouflage by masking an animals’ characteristic outline, thereby impairing recognition. It is hoped that these novel methods will ultimately provide a means to test if seemingly ‘disruptive’ markings, such as those of zebras, tigers or even soldiers uniforms function to disrupt recognition (Fig. 2).

This research will enable us to better understand—and design—camouflage patterns, as well as appreciate the beauty of animals colorations, that we sometimes don’t always see.

Fig 2: Tiger stripes have long been thought to provide camouflage, but it is difficult to know whether this camouflage is achieved exclusively through background matching, or also through disruption.

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Three minute presentation

The idea of a Three Minute Thesis (TMT) is to quickly and clearly communicate the rationale and importance for ones research. Simply put, can you condense the message of your research into a three-minute ‘elevator pitch’.

As part of my Ph.D. in Tom Sherratt’s lab, at Carlton University, I presented my work as a three-minute thesis. It was a really challenging and enjoyable activity… made all the more worthwhile when I was selected as a finalist for Carleton’s competition.