Avoiding detection through camouflage is often key to survival. However, an animal’s appearance is not the only factor affecting conspicuousness: background complexity also alters detectability. This has been experimentally demonstrated for both artificially patterned backgrounds in the lab and natural backgrounds in the wild, but only for targets that already match the background well. Do habitats of high visual complexity provide concealment to even relatively poorly-camouflaged animals? Using artificial prey which differed in their degrees of background matching to tree bark, we were able to determine their survival, under bird predation, with respect to the natural complexity of the background. The latter was quantified using low-level vision metrics of feature congestion (or ‘visual clutter’) adapted for bird vision. Higher background orientation clutter (edges with varying orientation) reduced the detectability of all but the poorest background-matching camouflaged treatments; higher background luminance clutter (varying achromatic lightness) reduced average mortality for all treatments. Our results suggest that poorer camouflage can be mitigated by more complex backgrounds, with implications for both camouflage evolution and habitat preferences.

Data file is: Rowe_at_al_data.txt    
Format: tab-delimited text    
Created: 24/03/2021    

Description of variables (columns)    
Block    "Experimental block (different part of study site on different dates): factor with 27 levels, 1 to 27."
Treatment    "Experimental treatment (varied average luminance): factor with 9 levels (1 = darkest, 9 = lightest)."
Replicate    "Replicate number, factor with 10 levels, nested within Block and Treatment."
Censored    "Binary code: 1 = bird predation, 0 = disappearance for any other reason (e.g. invertebrate predation) or survival to the end of the trial."
Day    "Day of disappearance: numeric, taking values 0 to 5. 0 indicates the replicate was lost before deployment (n=3)."
Notes    Plain text description of fate of target.
contrast.fc    Luminance contrast metric of feature congestion.
colour.fc    Colour contrast metric of feature congestion.
orientation.fc    Edge orientation metric of feature congestion.