SummarySeabirds are one of the most threatened avian taxa and are hence a high conservation priority. Managing seabirds is challenging, requiring conservation actions at sea (e.g. Marine Protected Areas - MPAs) and on land (e.g. protection of breeding sites). Important Bird and Biodiversity Areas (IBAs) have been successfully used to identify sites of global importance for the conservation of bird populations, including breeding seabirds. The challenge of identifying suitable IBAs for tropical seabirds is exacerbated by high levels of dispersal, aseasonal and asynchronous breeding. The western Indian Ocean supports ~19 million breeding seabirds of 30 species, making it one of the most significant tropical seabird assemblages in the world. Within this is the British Indian Ocean Territory (BIOT), encompassing 55 islands of the Chagos Archipelago, which supports 18 species of breeding seabird and one of the world’s largest no-take MPAs. Between January and March in 1975 and 1996, eight and 45 islands respectively were surveyed for seabirds and the data used to designate 10 islands as IBAs. A further two were proposed following an expedition to 26 islands in February/March 2006. Due to the historic and restricted temporal and spatial nature of these surveys, the current IBA recommendations may not accurately represent the archipelago’s present seabird status and distribution. To update estimates of the BIOT breeding seabird assemblage and reassess the current IBA recommendations, we used seabird census data collected in every month except September from every island, gathered during 2008–2018. The maximum number of breeding seabirds for a nominal year was 281,596 pairs of 18 species, with three species making up 96%: Sooty Tern Onychoprion fuscatus - 70%, Lesser Noddy Anous tenuirostris - 18% and Red-footed Booby Sula sula - 8%. Phenology was a complex species-specific mix of synchronous and asynchronous breeding, as well as seasonal and aseasonal breeding. Nine of the 10 designated IBAs and the two proposed IBAs qualified for IBA status based on breeding seabirds. However, not every IBA qualified each year because Sooty Terns periodically abandoned breeding islands and Tropical Shearwater Puffinus bailloni breeding numbers dropped below IBA qualifying criteria in some years. Further, one survey per year does not always capture the periodic breeding of some tropical seabirds. We propose therefore, that IBAs in BIOT are better designated at the island cluster level rather than by specific island and require two surveys six months apart per year. This work highlights the merits of long-term, systematic, versus incidental surveys for breeding tropical seabirds and the subsequent associated designation of IBAs.

中文翻译：

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繁殖海鸟的现状和物候以及英属印度洋领地重要鸟类和生物多样性地区的回顾

摘要海鸟是最受威胁的鸟类分类群之一，因此是高度保护的优先事项。管理海鸟具有挑战性，需要在海上（例如海洋保护区 - MPA）和陆地（例如保护繁殖地）采取保护行动。重要鸟类和生物多样性区域 (IBA) 已成功用于确定对保护鸟类种群（包括繁殖海鸟）具有全球重要性的地点。为热带海鸟确定合适的 IBA 的挑战因高度分散、非季节性和异步繁殖而加剧。西印度洋支持约 1900 万只 30 种海鸟繁殖，使其成为世界上最重要的热带海鸟群落之一。其中包括英属印度洋领地 (BIOT)，包括查戈斯群岛的 55 个岛屿，它支持 18 种繁殖海鸟，是世界上最大的禁捕海洋保护区之一。在 1975 年和 1996 年 1 月至 3 月期间，分别对 8 个和 45 个岛屿进行了海鸟调查，数据用于将 10 个岛屿指定为 IBA。在 2006 年 2 月/3 月对 26 个岛屿进行探险之后，又提出了另外两个建议。由于这些调查的历史性和时间和空间限制，目前 IBA 的建议可能无法准确反映群岛目前的海鸟状况和分布。为了更新对 BIOT 繁殖海鸟组合的估计并重新评估当前的 IBA 建议，我们使用了除 9 月之外的每个月从每个岛屿收集的海鸟普查数据，这些数据在 2008 年至 2018 年期间收集。名义年繁殖海鸟的最大数量为 18 种 281,596 对，甲虫- 70%，小诺迪腱鞘囊肿- 18% 和红脚鲣鸟苏拉苏拉——8%。物候学是同步和异步育种以及季节性和非季节性育种的复杂物种特异性组合。10 个指定的 IBA 中的 9 个和提议的两个 IBA 符合基于繁殖海鸟的 IBA 身份。然而，并非每个 IBA 每年都获得资格，因为乌燕鸥会定期放弃繁殖岛和热带海鸥海鹦在某些年份，育种数量低于 IBA 资格标准。此外，每年的一项调查并不总能捕捉到一些热带海鸟的周期性繁殖。因此，我们建议，BIOT 中的 IBA 最好在岛屿集群级别而不是特定岛屿上指定，并且需要每年间隔六个月进行两次调查。这项工作突出了对热带海鸟繁殖进行长期、系统和偶然调查的优点，以及随后对 IBA 的相关指定。