The survival value of countershading with wild birds as predators

Abstract

Experiments were carried out on garden lawns in England in which four types of green pastry prey were exposed to predation by wild birds. The prey were dark green, light green, countershaded (dark green above, light green below) and reverse shaded (i.e. identical to countershaded but laid out upside‐down). Birds took significantly fewer countershaded prey than any of the other types thereby demonstrating the survival value of countershading.

Optimizing countershading camouflage

“…However, previous experiments that used a two-tone prey (e.g., refs. [21][22][23][24] showed an advantage for countershading over uniform background-matching dark green. As mentioned in the Introduction, it was not the case that all these experiments were carried out on sunny days, nor were the prey carefully aligned to the sun [as in the present study and necessary for countershading to function in direct illumination (18)].…”

“…There were seven treatments: the predicted optimal countershading for a sunny day (SunnyCS), the predicted optimal countershading for a cloudy day (CloudyCS), the darkest color of the countershaded treatments (Dark; equivalent to the background matching color for a flat object), the lightest color on the sunny countershaded treatment (Light), the mean of the sunny countershaded treatment (SunnyMean), the mean of the cloudy countershaded treatment (CloudyMean), and a two-tone countershaded treatment (TwoToneCS) that had the colors of the Dark and Light treatment but with a sharp boundary rather than a gradient. The latter treatment was included because it is qualitatively similar to the type of countershading used in previous experiments, where dark and light green pastry dough have been stuck together (21)(22)(23)(24).…”

“…Although some tests with artificial prey show reduced avian predation rates on two-tone, dorsally darker treatments (21)(22)(23)(24), the relationship between the color contrasts in these experiments and the predicted optima are unknown. We have recently filled this important gap by using a general theory of optimal countershading to derive the predicted optimal patterns for different weather conditions at a specific location, time of year and day (25).…”

“…Modeling of the light field shows that a sharp transition between dark and light, as used in previous experimental studies, provides optimal countershading only in direct, overhead sunlight (25). Only one of the previous experimental studies (24) was carried out under conditions where direct sun was a plausible illuminant, the others taking place in woodland (22) or including trials with overcast or rainy weather (21), or carried out in winter (21,23). This mismatch between the illuminant and the correct countershading pattern, and the fact that all previous experiments involved trials lasting throughout the day, when the sun is continually moving and so very different patterns of countershading are required for camouflage, raises the possibility that factors other than self-shadow concealment [e.g., disruptive coloration (9,13,26,27)] were responsible for detection differences.…”

Adaptive response to sociality and ecology drives the diversification of facial colour patterns in catarrhines

“…Facial colour pattern diversity in primates might also be driven by ecological demands for thermoregulation or camouflage, as the evolution of body colours in mammals is tied to these functions [4][5][6][7] . Although explicit tests for a link between ecology and facial diversity in catarrhines are lacking, ecological factors significantly predict levels of facial diversity in Neotropical primates (Platyrrhini), which form the sister group to catarrhines.…”