I think you may be thinking of Aderyn 'bird' or the plural form Adar 'birds'. But Adara itself is not a Welsh name, although it may be used in Wales. Dara is an Irish name often used for boys, sometimes in the forms Daragh or Darragh, but I'm not sure whether it's pronounced dahr-ah or dah-rer (long a or short a). Avaon is also not a traditional Welsh male name, although the name Afaon has some mythical reference. Have you been reading sci-fi novels?