Why does my dog tilt its head?
The head tilt is one of the more charming canine behaviours and does not have a single settled explanation, though several plausible contributors are supported.
Sound localisation is the most cited. Dogs locate sound partly by the slight difference in arrival time and intensity between their ears, and tilting may help refine that, particularly for frequencies or directions that are ambiguous. It may also adjust the position of the outer ear to collect sound more effectively.
Vision is a second suggested factor. A dog's muzzle occupies part of its lower visual field, and tilting may improve the view of a human face, particularly the mouth, which matters if the dog is reading expression and speech cues. This would predict that longer-muzzled dogs tilt more, and there is some support for that, though it is not conclusive.
A third element is learned reinforcement. Head tilting reliably produces delighted reactions, attention and often treats. Behaviour that is rewarded increases, so whatever the original cause, human response almost certainly strengthens it.
Research has also found an association between frequent head tilting and performance on tasks involving recalling the names of objects, which has been interpreted as the tilt accompanying concentration. That work is interesting rather than definitive.
One practical note deserves mention. A persistent head tilt that is present at rest rather than in response to a sound or a person, especially with loss of balance, circling or unusual eye movement, is different from the responsive tilt described here and warrants veterinary attention promptly.