The coloration of a bird must always be considered in respect to its behaviour and to its effect upon an observer, and is thus (almost as a rule) adaptive. Coloration characteristics fall broadly into two groups; those enhancing concealment or 'cryptic coloration', and those promoting conspicuousness or 'phaneric coloration'. Cryptic coloration is limited in its use to predator-prey relationships; either giving protection against an enemy (procryptic) or facilitating the capture of prey (anti-cryptic). Procryptic coloration is very common among birds, while anti-cryptic is rare. Strategies commonly used in cryptic coloration are: (1) General resemblance to the habitat, like the white plumage of the Snowy Owl and the closely ground-matching plumage of many larks. (2) Obliterative shading; the graded coloration ranging from dark(est) on the back to light(est) on the underparts which neutralises relief and gives the body an appearance as a flat surface. (3) Disruption; special patterns in the plumage delay the recognition by an observer because of attracting the attention to itself, away from the bearer. E.g. dark head-markings more or less hiding the eye in many birds (a good example is the Ringed Plover). (4) Special resemblance to a familiar object of the habitat, offering more a disguise than real concealment, like many nightjars which resemble fallen bits of wood. Phaneric coloration depends upon the exaggeration of colours or patterns, contours and relief. Counter-shading, to hide features as in cryptic coloration, is replaced by self-coloration which is quite remarkable in uniformly black or white birds (e.g. Spoonbills). Contours are often conspicuously framed with marginal patterns and frequently the eye has a prominent setting between the feathers. Also further adornments like plumes, fans, crests, ruffs, etc. are regularly used. This type of coloration has a function in courtship and display, threat and bluffing, social signalling and recognition and warning (e.g. to predators).