piar
chirp
peep
to make a high-pitched sound
+
-ar
verb suffix
Piar means to chirp and can be remembered by thinking of the English word peep0 (to make a high-pitched sound0) + -ar1 (verb suffix1).
verb
  1. chirp
    To chirp or tweet, as a bird.
    Los pollitos pían cuando tienen hambre. // The chicks chirp when they are hungry.