What structural difference contributes to the Willow Warbler's typically 'bright-eyed' facial expression?
Answer
The area immediately surrounding the eye is often paler than the crown feathers.
The facial features of the Willow Warbler contribute significantly to its identification, particularly when observing the region around the eye. While the pale supercilium is prominent, another key component creating the distinct look is the relative brightness of the area encircling the eye itself. This specific region, the lores and ocular area, is often observed to be paler than the feathers on the crown. This contrast, coupled with the long, pale supercilium juxtaposed against a darker eye stripe running through the eye, contributes to the overall impression of a somewhat bright-eyed expression.
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