Data from: Background complexity and the detectability of camouflaged targets by birds and humans

Remaining undetected is often key to survival, and camouflage is a
widespread solution. However, extrinsic to the animal itself, the
complexity of the background may be important. This has been shown in
laboratory experiments using artificially patterned prey and backgrounds,
but the mechanism remains obscure (not least because ‘complexity’ is a
multifaceted concept). In this study, we determined the best predictors of
detection by wild birds and human participants searching for the same
cryptic targets on trees in the field. We compared detection success to
metrics of background complexity and ‘visual clutter’ adapted from the
human visual salience literature. For both birds and humans, the factor
that explained most of the variation in detectability was the textural
complexity of the tree bark as measured by a metric of feature congestion
(specifically, many nearby edges in the background). For birds, this
swamped any effects of colour match to the local surroundings, although
for humans, local luminance disparities between the target and tree became
important. For both taxa, a more abstract measure of complexity, entropy,
was a poorer predictor. Our results point to the common features of
background complexity that affect visual search in birds and humans, and
how to quantify them.