Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
pīpo, āre, v. n., to peep, pip, chirp: mugit bos, balat ovis, equi hinniunt, gallina pipat, Varr. ap. Non. 156, 25; of the hawk, Auct. Carm. Philom. 24.