Centre for Applied Conservation Research, University of British Columbia, Vancouver, British Columbia, Canada.
PLoS One. 2011;6(7):e22027. doi: 10.1371/journal.pone.0022027. Epub 2011 Jul 18.
Seabirds integrate information about oceanic ecosystems across time and space, and are considered sensitive indicators of marine conditions. To assess whether hypothesized long-term foodweb changes such as forage fish declines may be reflected in a consumer's life history traits over time, I used meta-regression to evaluate multi-decadal changes in aspects of egg production in the glaucous-winged gull (Larus glaucescens), a common coastal bird. Study data were derived from literature searches of published papers and unpublished historical accounts, museum egg collections, and modern field studies, with inclusion criteria based on data quality and geographic area of the original study. Combined historical and modern data showed that gull egg size declined at an average of 0.04 cc y(-1) from 1902 (108 y), equivalent to a decline of 5% of mean egg volume, while clutch size decreased over 48 y from a mean of 2.82 eggs per clutch in 1962 to 2.25 in 2009. There was a negative relationship between lay date and mean clutch size in a given year, with smaller clutches occurring in years where egg laying commenced later. Lay date itself advanced over time, with commencement of laying presently (2008-2010) 7 d later than in previous studies (1959-1986). This study demonstrates that glaucous-winged gull investment in egg production has declined significantly over the past ∼50-100 y, with such changes potentially contributing to recent population declines. Though gulls are generalist feeders that should readily be able to buffer themselves against food web changes, they are likely nutritionally constrained during the early breeding period, when egg production requirements are ideally met by consumption of high-quality prey such as forage fish. This study's results suggest a possible decline in the availability of such prey, and the incremental long-term impoverishment of a coastal marine ecosystem bordering one of North America's rapidly growing urban areas.
海鸟综合了有关海洋生态系统的时间和空间信息，被认为是海洋状况的敏感指标。为了评估长期食物网变化（如饲料鱼类减少）是否会随着时间的推移反映在消费者的生活史特征中，我使用元回归评估了普通沿海鸟类——银鸥（Larus glaucescens）的产卵方面在数十年间的变化。研究数据来自文献检索、已发表论文和未发表的历史记录、博物馆的蛋库以及现代实地研究，其纳入标准基于数据质量和原始研究的地理区域。综合历史和现代数据表明，从 1902 年（108 年）开始，海鸥蛋的大小每年平均减少 0.04 立方厘米，相当于平均蛋体积减少 5%，而在 48 年内，平均每窝产卵数从 1962 年的 2.82 个减少到 2009 年的 2.25 个。在给定年份中，产卵日期与平均窝卵数呈负相关，即产卵开始较晚的年份，窝卵数越小。产卵日期本身随着时间的推移而提前，目前（2008-2010 年）的产卵开始时间比以前的研究（1959-1986 年）晚 7 天。本研究表明，银鸥在卵生产上的投资在过去约 50-100 年中显著下降，这种变化可能导致最近的种群数量下降。尽管海鸥是杂食性觅食者，应该能够轻易地缓冲食物网变化的影响，但它们在繁殖早期可能会受到营养限制，因为此时通过食用高质量的猎物（如饲料鱼类）来满足产卵的需求。本研究的结果表明，这种猎物的供应可能减少，以及毗邻北美一个快速发展的城市地区的沿海海洋生态系统逐渐变得贫瘠。
