Figure 1.

Colourful signals with achromatic backgrounds in birds. Many species of birds have colourful signals or ornaments displayed against largely achromatic surrounding backgrounds that may affect detection and discrimination of the signal. (a) Painted finch (Emblema pictum), (b) European robin (Erithacus rubecula), (c) red-bellied woodpecker (Melanerpes carolinus), (d) red-winged blackbird (Agelaius phoeniceus), (e) zebra finch (Taeniopygia guttata) and (f) tufted titmouse (Baeolophus bicolor). All images are from Wikimedia Commons. (Online version in colour.)