Translation:Have you remembered your father's birthday?
Yes, the reflexive acts as a passive form of sorts (in fact, it was passive in Latin, "recordari"): "ricordarsi di " is "to be reminded of", "to recall". The active form is transitive, so it would be "Hai ricordato il compleanno di tuo padre?". The two forms have basically the same meaning, but the reflexive is more common nowadays.
f.formica - If you are still there...? Why is the auxiliary "essere" and not "avere" ? Is it necessary because of "ricordare" being something special? As you know German you could maybe help me here. We say in German "Hast du an den Geburtstag deines Vaters gedacht? and not "Bist du ......? Thank you for your help.
No, the rule (you might remember) is that reflexive verbs always use "essere", and here the reflexive form is used: it's more evident in a third person, e.g. "lei si è ricordata del compleanno" (she remembered the birthday - "si" is reflexive, so essere is used) vs "lei le ha ricordato il compleanno" (she reminded her of the birthday - "le" isn't reflexive, so she and her are two different people and avere is used).
I'm wondering the same. I suppose that the two sentences are SLIGHTY different in English... "Have you remembered" sounds like someone asking me BEFORE the fact, where I might answer "Oh dear, NO! I'll get a card right away, and thank you for reminding me", whereas "You remembered?" would likely get the reply "No, I'm an idiot, and he's very annoyed with me because I forgot" ... I would love a native Italian speaker to comment on this one!!
Why is the verb essere used here ? when i look on this page http://italian.about.com/library/verb/blverb_ricordare.htm at passato prossimo they only use avere (ho ricordate, hai ricordate, ha ricordate etc...)