To make an unpleasantly loud, sharp cry. (Cambridge Dictionary)
To complain about something noisily. (Cambridge Dictionary)
(of a bird) make a loud, harsh noise. (Oxford Dictionaries)
(of a person) say something in a loud, discordant tone. (Oxford Dictionaries)
Complain or protest about something. (Oxford Dictionaries)
To utter a harsh abrupt scream. (Merriam – Webster)
To complain or protest loudly or vehemently. (Merriam – Webster)
When a bird squawks, it makes a loud harsh noise. (Collins Dictionary)
Why does my budgie, scream, chirp, squawk?
Do birds talk when they squawk?