When Common Birds Became Rare: Historical Records Shed Light on Long-Term Responses of Bird Communities to Global Change in the Largest Wetland of France

Many species have suffered large population declines due to the anthropogenic influence on ecosystems. Understanding historical population trends is essential for informing best efforts to preserve species. We propose a new method to reconstruct the past structure of a regional species pool, based on historical naturalist literature. Qualitative information collected from annotated checklists and reports can be relevant to identify major long-term community changes. We reviewed ornithological literature on the Camargue, the largest wetland in France. We reconstructed the entire breeding bird community from 1830 to 2009 and translated historical data into semi-quantitative data. This data permitted a calculation of a Community Commonness Index to measure the average level of abundance of species in a community. The Community Specialization and Community Temperature Indices were used to evaluate the potential long-term impact of land-use and climate changes on the composition of the regional bird species pool. We found a decrease in average abundance and specialization between 1950 and 1989, suggesting that changes in land-use negatively impacted the structure and composition of the local bird community by reducing species abundance and removing habitat-specialists (e.g. Southern Grey Shrike, Greater Short-toed Lark). These results are likely to be linked with a major loss of natural habitats in the Camargue between 1942 and 1984 when natural areas and traditional farmland were converted into intensive cultivated lands. We also found fluctuations among species with high versus low temperature preference. However, long-term effects of climate change on the bird community might be blurred by the impact of land-use changes. Overall, our results contrast with those obtained from well-monitored colonial waterbirds showing long-term increases. Our results plead for a more regular use of historical naturalist data when examining long-term changes in species communities as they allow the establishment of an older temporal point of reference and consideration of species not covered by traditional monitoring schemes.

由于人类活动对生态系统的干扰，诸多物种种群数量大幅下降。明晰种群的历史变化趋势，对于制定最优物种保护策略至关重要。我们提出一种基于历史博物学文献的新方法，用于重构区域物种种库（regional species pool）的历史结构。从带注释的名录与报告中获取的定性信息，可用于识别群落的长期重大变化。我们梳理了针对法国最大湿地卡马格（Camargue）的鸟类学文献，重构了1830年至2009年的完整繁殖鸟类群落，并将历史数据转化为半定量数据。基于该数据集，我们可计算群落常见度指数（Community Commonness Index），用以衡量群落内物种种群的平均丰度水平；同时采用群落特化指数（Community Specialization Index）与群落温度指数（Community Temperature Index），评估土地利用与气候变化对区域鸟类物种种库组成的潜在长期影响。我们发现1950年至1989年间，种群平均丰度与群落特化水平均出现下降，这表明土地利用变化通过降低物种种群丰度、移除栖息地特化物种（如南灰伯劳（Southern Grey Shrike）、大短趾百灵（Greater Short-toed Lark)），对本地鸟类群落的结构与组成产生了负面影响。上述结果或与1942年至1984年间卡马格地区的自然栖息地大规模丧失直接相关——此期间自然区域与传统农田被改造为集约化耕地。我们还观察到温度偏好不同的物种呈现出种群波动差异，但土地利用变化的影响可能掩盖了气候变化对鸟类群落的长期效应。总体而言，我们的研究结果与监测完善的集群水鸟种群长期增长的相关结论相悖。我们的研究结果呼吁，在探究物种群落的长期变化时，应更常态化地运用历史博物学数据——这类数据可提供更早的时间参照基准，同时能覆盖传统监测方案未纳入的物种。