Data from: Gray plumage color is more cryptic than brown in snowy landscapes in a resident color polymorphic bird

Camouflage may promote fitness of given phenotypes in different
environments. The tawny owl (Strix aluco) is a colour polymorphic species
with a grey and brown morph resident in the Western Palearctic. A strong
selection pressure against the brown morph during snowy and cold winters
has been documented earlier but the selection mechanisms remain
unresolved. Here we hypothesise that selection favors the grey morph
because it is better camouflaged against predators and mobbers in snowy
conditions compared to the brown one. We conducted an online citizen
science experiment where volunteers were asked to locate a grey or a brown
tawny owl specimen from pictures taken in snowy and snowless landscapes.
Our results show that the grey morph in snowy landscapes is the hardest to
detect whereas the brown morph in snowy landscapes is the easiest to
detect. With an avian vision model we show that, similar to human
perceivers, the brown morph is more conspicuous than the grey against
coniferous tree trunks for a mobbing passerine. We suggest that with
better camouflage, the grey morph may avoid mobbers and predators more
efficiently than the brown morph and thus survive better in snowy
environments. As winters are getting milder and shorter in the species
range, the selection periods against brown colouration may eventually
disappear or shift poleward.