Figure 2
From: The carotenoid-continuum: carotenoid-based plumage ranges from conspicuous to cryptic and back again
Relationship between carotenoid-based colouration (chroma) and detectability (visual contrast) against average green backgrounds. Upper panels correspond to green and lower panels to yellow plumage of blue tits (left), great tits (centre) and greenfinches (right). Each panel depicts the raw data for males, females and fledglings separately. Filled symbols above correspond to U-type eyes while the open symbols below belong to V-type eyes (note that for the greenfinch back there is much overlap between both eye types).