I have a young cockerel with birchen coloring. He came from a brown red bantam male crossed with a black hen that obviously carried the sex-linked silver (S) gene. So technically he is half brown red, half birchen, but so far he looks pure birchen. I plan to mate him with brown red females to produce birchen females. Such a cross will produce, theoretically, half birchen and half brown red females, all of which are pure birchen or pure brown red since the color is based on either (S) silver or (s) gold.