Second Prebasic Molt of a Black-headed Gull at Anchorage, Alaska

Q4 Agricultural and Biological Sciences Western Birds Pub Date : 2024-03-15 DOI:10.21199/wb55.1.5
Robert L. Scher
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Abstract

A second-cycle Black-headed Gull (Chroicocephalus ridibundus), a rare to casual visitor in western North America, remained at Anchorage, Alaska, from 16 July through 17 September 2023, providing a unique opportunity to track and document most stages of its second prebasic molt into definitive (adult) basic plumage. I estimated that the Anchorage bird required approximately 3 to 3.5 months (early/mid-June through late September) to complete the molt of its primaries. This is notably longer than the “average” 2.5 months stated for second-cycle Black-headed Gulls in several publications, but consistent with the duration and calendar limits reported by others for the entire species (mid-May/June through September). The start and duration of rectrix molt relative to the stage of primary molt closely matched that described for gulls in general, and specifically for predefinitive Bonaparte’s (C. philadephia) and Western (Larus occidentalis) gulls. When first observed in mid-July, the Anchorage bird had a white tail, as in definitive plumage, a trait infrequent in first-cycle Black-headed Gulls; then it molted the tail again through August. Although Black-headed Gulls occurring in western North America have been presumed to originate from eastern Asia, the timing of the Anchorage bird’s primary molt closely matched that published for second-cycle Black-headed Gulls in Europe, which has reported to be earlier—though molt schedules of Charadriiformes at the population level are highly variable.
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阿拉斯加安克雷奇一只黑头鸥的第二次前期蜕皮
2023 年 7 月 16 日至 9 月 17 日,一只北美洲西部稀有的第二周期黑头鸥(Chroicocephalus ridibundus)停留在阿拉斯加的安克雷奇,这为我们提供了一个独特的机会,跟踪和记录其第二次基本羽蜕变为最终(成年)基本羽的大部分阶段。据我估计,这只安克雷奇鸟需要大约 3 到 3.5 个月(6 月初/中旬到 9 月末)才能完成初羽蜕皮。这明显长于一些出版物中所说的第二周期黑头鸥 "平均 "2.5 个月的时间,但与其他人报告的整个物种的持续时间和日历限制(5 月/6 月中旬到 9 月)一致。与初级蜕皮阶段相对应的矩阵蜕皮的开始时间和持续时间与一般海鸥的描述非常吻合,特别是与预知的波拿巴海鸥(C. philadephia)和西方海鸥(Larus occidentalis)的描述非常吻合。在 7 月中旬首次观察到这只安克雷奇鸟时,它的尾巴是白色的,就像最终羽色一样,这种特征在第一周期的黑头鸥中并不常见。虽然北美洲西部出现的黑头鸥被推测来自亚洲东部,但安克雷奇鸟的初次蜕皮时间与欧洲公布的第二周期黑头鸥的蜕皮时间非常吻合,据报道,欧洲黑头鸥的蜕皮时间更早--尽管黑头鸥在种群水平上的蜕皮时间表变化很大。
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来源期刊
Western Birds
Western Birds Agricultural and Biological Sciences-Animal Science and Zoology
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0.60
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