What is a primary clinical sign of ear infections in dogs?

Head shaking or scratching at the ears is a primary clinical sign of ear infections in dogs. This behavior often indicates discomfort or irritation in the ear canal, prompting the dog to try to alleviate the sensation. When an infection occurs, inflammation can lead to a range of symptoms, with frequent shaking of the head and pawing or scratching at the ears being among the most noticeable. This is the dog's instinctual response to the pain or itchiness caused by the infection.

The other choices do not specifically correlate with ear infections. Excessive barking may result from various behavioral issues or distress but is not a definitive indicator of an ear problem. Increased drinking can be associated with metabolic issues or conditions like diabetes, rather than an ear infection. Loss of fur typically points to skin-related issues such as allergies, parasites, or other dermatological conditions, not an infection of the ear itself.