Cats chirp at birds mainly due to their natural hunting instincts. This chirping or chattering sound is believed to be an expression of excitement or anticipation when the cat sees potential prey, such as birds or squirrels. The behavior may also mimic bird sounds to entice the prey closer or may represent an involuntary reflex related to the cat's jaw movements mimicking the killing bite used in hunting. Often, the chirping can also express frustration or excitement from not being able to reach the prey, especially if the cat is observing through a window. This behavior is normal and reflects a cat's instinctual prey sequence starting from watching the prey to eventually stalking and hunting it. Experts also suggest that chirping is a way for cats to express their engagement with their environment and entertain themselves, as they watch what can be likened to "kitty cat TV" through the window. This behavior is harmless and a sign of a cat acting on its predatory nature.
