how do we know a song thrush must have ears???

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To determine if a song thrush must have ears, we can consider the anatomy and physiology of birds in general. While we cannot directly observe the presence of ears on a bird like a song thrush, we can infer their existence through a few key factors:

1. Universal trait: Ears are a universal trait in birds. All bird species possess ears, although the location and appearance may vary. Ears play a vital role in their ability to hear sound, communicate, and navigate their environment.

2. Sound perception: Birds rely heavily on sound for communication, mate attraction, warning signals, and hunting. Like most animals, birds have evolved ears to detect and process sound waves. Without ears, birds would not be able to perceive the intricate melodies they produce or respond to the calls of other birds.

3. Feather structure: Birds have specialized feathers that help localize sound to their ears. These feathers, known as "aural feathers" or "ear tufts," are found around their ear openings and direct sound waves towards the ears. This anatomical adaptation further reinforces the presence of ears in birds, including song thrushes.

While direct observation of the ears may be challenging in many bird species, the functions they serve, the evolutionary presence of ears in all birds, and the external structures surrounding the ear openings all strongly indicate that a song thrush, as a bird, must indeed have ears.