Why do black berries often stain bird faeces?

Abstract

Several plant species produce deep black or purplish-black fruits. The colour of these fruits is usually due to a concentrated solution containing Anthocyanins in the cells of the epicarp or pericarp of these fruits. Anthocyanins are easily hydrolysed to Anthocyanidins, but these too have deep colours. The Anthocyanidins produced by the breakdown of the tissues of black fruits are usually deep purplish violet. It is the high concentration of pigment which makes the fruit appear black.