Maran chicks - cuckoo vs black

[TGinTX]

I have received some ‘dark brown egg layer’ chicks through the mail and I can tell 4 are likely Marans. They are possibly French black or cuckoo. Is there anything that distinguishes the chick breeds? I’m assuming I won’t know until the wing feathers get long enough to see if they are barred or not. But I thought I’d check if anyone knew how to tell.

 

[ve]

Cuckou's will have small white dot (or bigger) on top of the head. Black-Coper will not.