Striking centennial-scale changes in the population size of a threatened seabird

Many animal populations are under stress and declining. For numerous marine bird species, only recent or sparse monitoring data are available, lacking the appropriate temporal perspective needed to consider natural, long-term population dynamics when developing conservation strategies. Here we use a combination of established paleoenvironmental approaches to examine the millennial-scale dynamics of the world’s largest colony (representing ~50% of the global population) of the declining and vulnerable Leach’s Storm-petrel (Hydrobates leucorhous). By reconstructing the last ~1,700 years of the colony’s population trends, we corroborate recent surveys indicating rapid declines since the 1980s. More surprisingly, however, was that population size was smaller and has changed strikingly in the past, even prior to the introduction of human stressors. Our results challenge notions that very large colonies are generally stable in the absence of anthropogenic pressures and speak to an increasingly pressing need to better understand inter-colony movement and recruitment when inferring range- and species-wide trends. While the recently documented decline in storm-petrels clearly warrants conservation concern, we show that colony size was consistently much lower in the past and changed markedly in the absence of major anthropogenic activity. In response, we emphasize the need for enlarged protected area networks to maintain natural population cycles, coupled with continued research to identify the driver(s) of the current global seabird decline.诸多动物种群正承受生存压力，种群数量持续下滑。对于多数海鸟物种而言，当前仅能获取新近或零散的监测数据，难以在制定保护策略时，纳入自然种群长期动态分析所需的完整时间维度视角。本研究结合成熟的古环境研究方法，对全球规模最大的白腰叉尾海燕（Leach’s Storm-petrel，Hydrobates leucorhous）繁殖群落（占该物种种群全球总量约50%）开展千年尺度的种群动态分析——该物种正处于数量下滑且易受威胁的状态。通过重建该繁殖群落过去约1700年的种群变化趋势，本研究验证了近期调查结果：自20世纪80年代起，该种群正经历快速下降。然而更令人意外的是，即便在人类活动施加生存压力之前，该种群在历史上也曾长期处于较低规模，且种群数量曾发生剧烈波动。本研究结果对"大型繁殖群落若无人为压力则通常保持稳定"的传统认知提出了挑战，同时表明，在推断物种整体及分布范围内的种群趋势时，我们亟需更深入地厘清不同繁殖群落间的种群移动与补充机制。尽管近期记录到的叉尾海燕种群下降显然值得保护领域高度关注，但本研究证实，该繁殖群落的历史种群规模始终远低于当前认知水平，且在未受重大人类活动影响的时期，种群数量也曾出现显著变化。据此，本研究强调，需扩大保护区网络以维持其自然种群周期，同时应持续开展研究以明确当前全球海鸟种群下降的驱动因素。