@marchick
here the method you should use if you want to breed your Blue Birchen ,I think you should .they are great birds .no much work is needed to get them 100% perfect .
Step one=work with both your cockerels .and 2 pens .
Pen1= old cockerel { Need Name } mate him to the 2 Birchen pullets and a Silver cuckoo pullet..you ll get nice pullets and cockerels .most of them will be well marked with a pure silver.
Pen 2 = Young cockerel mate him to your Blue Birchen pullets .
Step 2 = after you hatch a good number of chicks from both pen ,SWAP the rooster .the older will go to pen2 and the youngest will go to pen 1 . hatch a god number of chicks and select the best one .
if you do I m telling to do you ll have a correct Birchen marans Blue and Black correct in all aspect in no time . your chooks don t have many fault as flock .
let me know if you are interested and I ll explain to you more different steps of breeding
chooks man