Background complexity can mitigate poor camouflage

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. Funding provided by: Biotechnology & Biological Sciences Research Council, UKCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000268Award Number: BB/S00873X/

Red deer Cervus elaphus blink more in larger groups

Most animals need to spend time being vigilant for predators, at the expense of other activities such as foraging. Group-living animals can benefit from the shared vigilance effort of other group members, with individuals reducing personal vigilance effort as group size increases. Behaviors like active scanning or head lifting are usually used to quantify vigilance but may not be accurate measures of this. We suggest that measuring an animal's blinking rate gives a meaningful measure of vigilance: increased blinking implies reduced vigilance, as the animal cannot detect predators when its eyes are closed. We describe an observational study of a captive population of red deer, where we measured the blinking rates of individual deer from groups of differing sizes (where mean group size ranged between 1 and 42.7 individuals). We demonstrate that as group size increases in red deer, individuals increase their blink rate, confirming the prediction that vigilance should decrease. Blinking is a simple non-invasive measure and offers a useful metric for assessing the welfare of animals experiencing an increase in perceived predation risk or other stressors

Red deer Cervus elaphus blink more in larger groups

Most animals need to spend time being vigilant for predators, at the expense of other activities such as foraging. Group-living animals can benefit from the shared vigilance effort of other group members, with individuals reducing personal vigilance effort as group size increases. Behaviors like active scanning or head lifting are usually used to quantify vigilance but may not be accurate measures of this. We suggest that measuring an animal's blinking rate gives a meaningful measure of vigilance: increased blinking implies reduced vigilance, as the animal cannot detect predators when its eyes are closed. We describe an observational study of a captive population of red deer, where we measured the blinking rates of individual deer from groups of differing sizes (where mean group size ranged between 1 and 42.7 individuals). We demonstrate that as group size increases in red deer, individuals increase their blink rate, confirming the prediction that vigilance should decrease. Blinking is a simple non-invasive measure and offers a useful metric for assessing the welfare of animals experiencing an increase in perceived predation risk or other stressors

How background complexity impairs target detection

Camouflage is frequently used by animals for concealment and thereby improves survival. Typically, it is the animal’s own colour and patterning which is expected to affect its detectability; however the complexity of the background can also have an influence. Although there is a growing literature examining this, the underlying exact mechanism is unknown. In this paper we address this issue by using humans as proxy ‘predators’ in a computer-based search task and monitoring their detection times for targets on varying backgrounds. By using artificial greyscale targets and backgrounds, we were able to isolate and manipulate the normally covarying factors which comprise ‘complexity’ in natural habitats. We show that reduced detection is not explained by greater information content (entropy) or higher variance in the background’s features per se, but instead by reduced signal-to-noise ratio in the visual features that potentially distinguish target from background. This raises questions about when the term complexity should be used, and how observers learn the characteristics of a backgroun