Hi rancher, sorry if I missed your orginal birchen post. I don't always get all the way through the posts every day, I must of missed seeing it somehow..
Several of us recently became interested in raising the silver birchens. The silver birchens are
supposed to be about the same as the BCMs except for having the silver replacing the copper, from what I understand. However, I have noticed with many of the ones I've seen that the egg color needs improvement, they don't seem to get as large so the body/barn needs to be built larger, some have feathered shanks but many do not so that needs improvement. Many of the hens seem to show mossiness on the bodies especially the silver black females.
As far as temperment goes, they seem very similar to the Bl and blk coppers. I only have 3 birchens (a blue male, a blue female, and a blk female). Only my blue female has started laying so far (about the same avg age as a bcm) and her egg color is an improvement over the egg she hatched from but still needs improvement! Both of the females are very sweet and friendly to people. Both of the females seem very aggressive to cats lol! One female the bl birchen thinks she is a turkey so I knew she was an aggressive thing but then the blk birchen who is related but younger turned out to have the same personality and she was only raised with chickens. Niether girl will take crap from chickens or other animals. The cockeral is just now going through a protective phase (wow I have girls and they are mine!) but is very sweet when I pick him up and handle him. He doesn't like me to pick up the blk birchen girl though lol.
There is no APA standard for silver birchen as of yet. I think so far just the BCM and Wheaten Marans have been accepted.
I like this site for Marans descriptions even though it isn't American. Scroll down to the Birchen description. It has some photos of nice birchens and genetic description.
http://frenchmaransclubaustralia.yolasite.com/notes-on-breeding.php
Vicki has been tooling around with the silver birchens longer than I have so can probably add better/additional observations...