The Chocolate Orpington is a relatively new colour of Orpington and currently to my knowledge only exists in bantam size although I'm sure it won't be long before they are crossed into large fowl.
The choc gene responsible for the chocolate colour was discovered by the late Dr. Clive Carefoot around 1993-1994. It is a rare Sex-Linked Recessive gene that is basically a dilution of black pigment. This means that out of a pair of genes, the female will be chocolate with just one copy of the gene but the male requires two copies of the choc gene to look chocolate. This also means that black males can look black, but can be carrying one copy of the chocolate gene which can be passed to his prodgeny.
Chocolate Orpingtons are slow to feather up. This is thought to be a direct result of the choc gene. Black Orpingtons are slow at feathering up but Chocolate Orps are even slower. They lay a slightly tinted egg.
Chocolate Orpingtons breed true - but there are some breeding combinations that are worth noting:
Black males carrying the chocolate gene are called 'Split' cockerels.
Photo: Chocolate Orpington Cock (Bantam) courtesy of Matt Hanson.