The Eurasian Treecreeper (Certhia familiaris) has an effective camouflage against mammalian but not avian vision in boreal forests

A well-known example of visual camouflage in birds is the plumage coloration of the Eurasian Treecreeper Certhia familiaris, yet this species’ camouflage has never been objectively quantified. Here, we quantify treecreeper camouflage in its boreal forest habitat, test whether treecreepers better match tree backgrounds at nest site, territory or habitat spatial scales, and explore which common tree species provide the best background match. Using photographic data of the birds and forested backgrounds, we test their background match using human, ferret and avian vision modelling. We found that a treecreeper’s wing and mantle provided closest background matching, whereas the wing stripe and t…