Significance of plumage colour for winter survival in the Tawny Owl (Strix aluco): revisiting the camouflage hypothesis

Abstract

In snowy winters, the survival of Tawny Owls Strix aluco of the grey colour morph is suggested to be better than that of the brown (or red) morph, partly due to their paler plumage, which is presumed to provide better camouflage against predation. If the difference in the susceptibility to predation between the colour morphs is significant, this should probably be reflected in the relation between the number of snow‐covered days (i.e. the length of the winter) and the number and survival of owls of different colour. In a population in southern Finland there were no significant associations between the number of snowy days during winter and the number of breeding Tawny Owls of different colour morphs in the following spring, but the number of owls, in particular red ones, varied inversely with the number of snowy days in the winter of the previous year. The time lag suggests that the number of snow‐covered days (or some related factors) primarily influenced the pre‐breeding survival of young red owls. However, I found no effect of snow days on the proportion of colour morphs, suggesting only small differences in morph‐specific survival under long‐lasting winter conditions.

Numerical Response of Owls to the Dampening of Small Mammal Population Cycles in Latvia

“…The observed depression of the STRALU population from 2010 to 2012 in Latvia partially matched with Lithuania [ 36 ]. This was likely the consequence of two consecutive snow-rich winters, with multiple freeze—thaw events forming ice sheets in snow cover—factors reducing species survival [ 45 , 162 , 163 ]. This event did not affect breeding performance, and the population recovered quickly.…”

Enclosure Background Preferences Differ between Sexes and Color Morphs in the Gouldian Finch

“…The study specifically tested whether Gouldian finches prefer complex over simple backgrounds. While background matching with respect to colors is an important aspect of camouflage [ 6 , 8 , 19 , 20 , 21 ], we did not try to match background colors with plumage colors due to the potentially different perception of colors by the birds (tetra-chromatic vision [ 48 ]). However, the complexity of backgrounds alone has been shown to reduce predation [ 40 ].…”

“…Camouflage is achieved by matching the average background [ 11 , 15 , 16 ] or specific aspects of the background (e.g., leaves) [ 17 ] and exploiting the perception and cognitive mechanisms of predators [ 18 ]. Reducing the contrast against the background has been shown to decrease detectability and hence predation [ 6 , 8 , 19 , 20 , 21 ]. It can affect population densities with higher densities in areas of better camouflage efficiency [ 16 ], support species divergence with recently diverged species showing a close match to the environment [ 20 ], and positively affect the invasion success of new habitats with better background matching.…”

“…For example, in the color polymorphic cichlid Amphilophus labiatus , morphs differed in their ability to match backgrounds, which coincided with their frequency [ 27 ]. Likewise, in Tawny owls ( Strix aluco ), the gray morph was less conspicuous against a snowy background and tree trunks, resulting in higher survival in snowy winters [ 19 , 21 ]. In other species, morphs match different backgrounds, affecting their microhabitat selection [ 28 , 29 ].…”

Numerical Response of Owls to Dampening of the Population Cycles of the Small Mammals in Latvia

“…Observed depression of STRALU population from 2010 to 2012 in Latvia partially matches with Lithuania [36]. We consider this to be a consequence of two consecutive snow-rich winters with multiple freeze-thaw events forming ice sheets in snow coverfactors reducing species survival [45,[164][165]. This event did not affect breeding performance and the population recovered quickly.…”