In the times of Chazal a reed (קנה) was used for writing (as is clear from Ta'anit 20b). When did the practice of writing with a feather begin? Also, since feathers did exist in those times, why did they not use them?
The Ashkenazic custom is to use a feather, and although Sephardic sofrim have been writing with reeds until recently, nowadays even most Sephardic sofrim use quills. (I have very close contact with many Sephardic sofrim and have found only one, a man in his 80s, who uses a reed.)