He can avoid most of the spray but a little bit burns his neck.
He quickly gets up and looses another two arrows at the bird creature
Rolls
Reflex save - Acid spray - (1d20+13)
(6) + 13 = 19
Short bow attack #1 - (1d20+7)
(10) + 7 = 17
Short bow attack #2 - (1d20+2)
(4) + 2 = 6
Potential damage #1 - (1d6)
(6) = 6
Potential damage #2 - (1d6)
(4) = 4