Alex (his name supposedly an acronym for Avian Learning Experiment) eventually learned the names of about 50 objects, knew the numerals from one to six, could perform simple addition and used categories such as similarity and difference, shape, colour and material.

ECONOMIST: Alex the African Grey

The colour has been used in ribbons and other publicity material since their daughter's disappearance.

BBC: Mid Wales

Dr Feld also has plans to use beams of different colours, since each colour has a slightly different refractive index in a given material.

ECONOMIST: Microscopy