Breeding Status of the Gray Vireo on the Baja California Peninsula

Q4 Agricultural and Biological Sciences Western Birds Pub Date : 2023-08-15 DOI:10.21199/wb54.3.1
L. Hargrove, P. Unitt, G. Marrón, Tonatiuh Gaona-Melo, G. Ruiz-Campos
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Abstract

Most of the breeding range of the Gray Vireo (Vireo vicinior) lies within the southwestern United States, where the population is sparse, patchy, and declining. But the species also breeds in Baja California, Mexico, where its status has not been assessed. To rectify this, in 2021 and 2022 we surveyed four mountain ranges where the Gray Vireo is known or might be expected. In the northernmost, the Sierra Juárez, we located 43 territories—an abundance strikingly greater than just across the border in Upper California. Territories were in both treeless chaparral dominated by chamise (Adenostoma fasciculatum) and redshank (A. sparsifolium), and in the extensive pinyon woodland. In the Sierra San Pedro Mártir, all 71 territories located were in Adenostoma-dominated chaparral. Extrapolation of the densities observed in these two ranges over the extent of suitable habitat implies the population of the Gray Vireo in Baja California should be over 10,000 individuals. Confirmed by audio recording, one sighting from the Sierra de Ulloa overlooking Ensenada suggests a still wider distribution in Baja California. Isolated stands of chaparral grow south of the Gray Vireo’s previously reported breeding range, on the Sierra La Asamblea. But our reconnaissance of it revealed no Gray Vireos. Survey of the Sierra San Francisco in the center of the peninsula, 3–9 April, revealed only 3 Gray Vireos, all in winter habitat containing Bursera microphylla. Therefore two molting specimens collected in the Sierra San Francisco in October 1997 imply that some individuals molt in the winter range, not a southward extension of the breeding range. Despite Baja California representing only a small part of the Gray Vireo’s breeding range spatially, it contributes disproportionately to the species’ population and therefore conservation.
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下加利福尼亚半岛灰鲤的繁殖状况
大多数育种范围的灰绿鹃(绿鹃vicinior)位于美国西南部,人口稀疏,参差不齐,下降。但该物种也在墨西哥下加利福尼亚州繁殖,其状况尚未得到评估。为了纠正这一点,在2021年和2022年,我们调查了四个已知或可能会有Gray Vireo的山脉。在最北端的塞拉Juárez,我们发现了43个领土——数量远远超过了上加利福尼亚州的边界。领地分布在以田鼠(Adenostoma fasciculatum)和红脚(a.s parsifolium)为主的无树灌木林和广阔的小林林地。在Sierra San Pedro Mártir,所有71个领地都位于腺瘤为主的灌木林中。在这两个范围内观察到的密度在合适栖息地范围内的外推表明,下加利福尼亚州的灰色维里奥的种群数量应该超过10,000只。经录音证实,从乌洛亚山脉俯瞰恩塞纳达的景象表明,下加利福尼亚的分布范围更广。在以前报道过的灰树的繁殖范围以南,在塞拉拉阿萨姆布里亚,生长着孤立的灌木林。但我们的侦察没有发现Gray Vireos。在4月3日至9日对半岛中部的旧金山山脉进行的调查中,仅发现了3只灰色病毒,均位于含有小叶Bursera的冬季栖息地。因此,1997年10月在旧金山山脉采集的两个换毛标本表明,一些个体在冬季范围内换毛,而不是向南扩展繁殖范围。尽管下加利福尼亚只占灰灰灰熊繁殖范围的一小部分,但它对灰灰灰熊的种群数量和保护做出了不成比例的贡献。
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来源期刊
Western Birds
Western Birds Agricultural and Biological Sciences-Animal Science and Zoology
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