Abstract

Populations of many vertebrates are declining and geographic ranges contracting, largely as a consequence of anthropogenic threats. Many reports of such decline, however, lack the breadth and detail to narrow down its causes. Here we describe population decline in the Common Loon (Gavia immer), a charismatic aquatic bird, based on systematic resighting and measurement of a marked population. During our 27-year investigation, age-adjusted chick mass has fallen by 11%, mortality among young and old chicks has increased by 31% and 82%, respectively, and fledging success has declined by 26%. Meanwhile, the return rate of marked nonbreeders (“floaters”) has plunged by 53%, and the adult population overall has declined by 22%. Consistent with the thinning ranks of floaters, the rate of territory eviction has decreased by 52% during the study. Despite the decline in floaters, territory occupancy remains unchanged. However, a matrix model, updated with recent estimates for breeding success, juvenile survival, and senescence, yields a recalculated deterministic population growth rate (λ) of 0.94 for our study population, which suggests that declines in vital rates could lead to a loss of 52% of the current population and a decline of 37% in territory occupancy by 2031. Lack of data on floaters in other upper Midwest and New England loon populations leaves their status in doubt.

中文翻译：

---

浮游生物的生存率下降导致普通潜鸟种群数量下降

 抽象的

许多脊椎动物的数量正在减少，地理范围正在缩小，这主要是由于人为威胁的结果。然而，许多有关这种下降的报告缺乏广度和细节来缩小其原因。在这里，我们基于对标记种群的系统重新观测和测量，描述了普通潜鸟 ( Gavia immer ) 的种群下降情况，这是一种魅力十足的水鸟。在我们长达 27 年的调查中，年龄调整后的雏鸡质量下降了 11%，幼雏和老年雏鸡的死亡率分别增加了 31% 和 82%，雏鸡成功率下降了 26%。与此同时，被标记的非繁殖者（“飞禽”）的回归率下降了 53%，成年人口总体下降了 22%。与流动人口数量的减少相一致的是，在研究期间，领土驱逐率下降了 52%。尽管飞蚊数量减少，但领土占用率保持不变。然而，根据最近对繁殖成功率、幼体存活率和衰老的估计进行更新的矩阵模型，重新计算出我们研究种群的确定性种群增长率 (λ) 为 0.94，这表明生命率的下降可能导致到 2031 年，潜鸟数量将占现有数量的 52%，领地占有率将下降 37%。由于缺乏其他中西部上游和新英格兰潜鸟种群的数据，它们的状况令人怀疑。