What specific anatomical feature might be observed at the base of the bill on certain swans like the Mute Swan?

Answer

A prominent basal knob or swelling.

If you get a close enough look at certain swans, like the Mute Swan, you might observe a prominent knob or basal swelling at the base of the bill, a feature rarely seen on geese.

What specific anatomical feature might be observed at the base of the bill on certain swans like the Mute Swan?

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Ducks, Geese, and Swans: What's the Difference? - YouTube

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