What is the specific diagnostic feature of the Sabine’s Gull tail that matures in immature birds?
Answer
Dark tail with a white trailing edge.
The tail pattern serves as a critical diagnostic feature for species recognition, particularly during the brief pairing season in the Arctic summer. Immature birds undergo a transition where their tail pattern changes from a mottled appearance to a definitive adult characteristic. This perfected feature is specifically described as being dark in color overall, but clearly delineated by a white trailing edge, which must be fully established before the bird commits to the intense demands of breeding displays.
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