Hello Corin,
Michael's birth would have been recorded at the local registry office like any other birth. There was no separate civil register for the Jews. It may also have been recorded in a Jewish register maintained by the Jewish community of Berlin.
Civil records from that era are held at:
Landesarchiv Berlin
Eichborndamm 115 - 121, D-13403 Berlin
Telefon: ++49 (0)30 90 264 - 0
E-Mail:
info@landesarchiv.berlin.deBecause Michael was born less than 110 years ago, you will have to prove that you are a direct relative to be able to obtain his birth cert.
I also found the names and dates of birth of Marianne's siblings, but I believe that you already have those.
As neither of his parents were German citizens and he was illegitimate anyway, he would have been regarded as an Austrian citizen based on the nationality of his mother.
Justin