Abstract
BackgroundCrypsis by background-matching is a critical form of anti-predator defence for animals exposed to visual predators, but achieving effective camouflage in patchy and variable natural environments is not straightforward. To cope with heterogeneous backgrounds, animals could either specialise on particular microhabitat patches, appearing cryptic in some areas but mismatching others, or adopt a compromise strategy, providing partial matching across different patch types. Existing studies have tested the effectiveness of compromise strategies in only a limited set of circumstances, primarily with small targets varying in pattern, and usually in screen-based tasks. Here, we measured the detection risk associated with different background-matching strategies for relatively large targets, with human observers searching for them in natural scenes, and focusing on colour. Model prey were designed to either ‘specialise’ on the colour of common microhabitat patches, or ‘generalise’ by matching the average colour of the whole visual scenes.ResultsIn both the field and an equivalent online computer-based search task, targets adopting the generalist strategy were more successful in evading detection than those matching microhabitat patches. This advantage occurred because, across all possible locations in these experiments, targets were typically viewed against a patchwork of different microhabitat areas; the putatively generalist targets were thus more similar on average to their various immediate surroundings than were the specialists.ConclusionsDemonstrating close agreement between the results of field and online search experiments provides useful validation of online citizen science methods commonly used to test principles of camouflage, at least for human observers. In finding a survival benefit to matching the average colour of the visual scenes in our chosen environment, our results highlight the importance of relative scales in determining optimal camouflage strategies, and suggest how compromise coloration can succeed in nature.
Highlights
Crypsis by background-matching is a critical form of anti-predator defence for animals exposed to visual predators, but achieving effective camouflage in patchy and variable natural environments is not straightforward
Generalist and specialist strategies in the field Volunteers were tasked with finding targets that adopted a generalist strategy, or that specialised on one of four microhabitat types
There was no interaction between weather and camouflage strategy, or any effect of weather conditions on detection risk, but there was a clear effect of strategy: generalists were detected at shorter distances than microhabitat specialists (hazard ratio for generalists versus specialists, Hazards ratios (HR) = 0.543, confidence interval (CI) = 0.443– 0.667, z = − 5.84, p < 0.001; Fig. 1), suggesting better camouflage efficacy
Summary
Crypsis by background-matching is a critical form of anti-predator defence for animals exposed to visual predators, but achieving effective camouflage in patchy and variable natural environments is not straightforward. Animals generally inhabit heterogenous natural environments, which often change seasonally, and some species must move between visually-distinct habitat patches to find food or mates; maintaining a good resemblance to all these potential backgrounds is challenging [9, 14, 15]. Behavioural adaptations, such as adjusting pattern orientation [16] or altering the background itself [17], can improve background-matching against heterogeneous natural backgrounds [18], while some species can even change their appearance to better adapt to their current environment [19]. For species with fixed colour patterns, how camouflage should be optimised in heterogeneous habitats remains an evolutionary puzzle
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