Panda has a simple question, how do the birds find you? Panda means some of the letters she recieves say " Where are you? " but they would have to know in order to send Panda a bird... Right?
I would theorise that the birds are elven bred. Things of magic that simply require the name of their recipient and then take flight, following the winds of magic that wrap around the continent of Asulon. Thats how I see it, anyway.