How is the Willow Warbler's pale supercilium generally characterized when contrasted with the Chiffchaff?
Answer
The Willow Warbler features a well-defined, long supercilium that often extends noticeably behind the eye.
Attention to the head pattern is crucial for identification. The Willow Warbler possesses a relatively distinct, pale supercilium, which is the stripe located above the eye. This eyebrow stripe is often described as well-defined and long, frequently contrasting nicely with the darker eye stripe that runs through the eye. Crucially, this pale stripe usually extends noticeably behind the eye. In contrast, the Chiffchaff is noted as having a supercilium that is shorter and less contrasting, making the length and prominence of the pale eyebrow stripe a key structural feature for the Willow Warbler.
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