Science Division, Washington Department of Fish and Wildlife, Olympia, Washington, United States of America.
US Forest Service Pacific Northwest Research Station, Olympia, Washington, United States of America.
PLoS One. 2022 Apr 21;17(4):e0267165. doi: 10.1371/journal.pone.0267165. eCollection 2022.
The marbled murrelet (Brachyramphus marmoratus) is classified as a threatened species under the US Endangered Species Act in Washington, Oregon, and California USA due to population declines, loss of breeding habitat, and other factors. To date, population assessments have focused on breeding season at-sea surveys. Consequently, there is little information on this species' distribution, abundance, and population trends during the non-breeding season, when murrelets are found exclusively in the marine environment. To address this information need, we assessed non-breeding (Sep-Mar) at-sea murrelet abundance patterns and population trends over 8 years, in a portion of its range where breeding season surveys indicate a 20-year population decline, Puget Sound, Washington, USA. This allowed us to assess whether non-breeding population trends mirrored those observed during the breeding season suggesting regional year-round conservation concerns and to also identify important over-wintering areas (areas of high abundance). We integrated our non-breeding abundance information with breeding season information to assess year-round patterns of abundance. This allowed us to test the prediction that murrelets move into the relatively protected inner marine waters of Puget Sound from harsher outer coastal habitats during the non-breeding season to molt and over-winter. Similar to trends from the breeding season, we observed strong murrelet density declines across the entire non-breeding period (Sep and Apr) with declines most pronounced in the fall and early winter (lateSep-Dec) survey windows when birds molt and in the spring just prior to breeding (Mar-Apr). Despite these declines, there was essentially no change in murrelet density in mid-winter (January-February) when overall density was lower. Puget Sound murrelet density exhibited a strong north-south gradient with relatively high densities to the north and low densities to the south; murrelets were largely absent from Central Puget Sound. For strata other than Central Puget Sound, density varied seasonally with birds more evenly distributed among strata between September and December but in the late winter/early spring period (Jan-Apr), murrelets were largely absent from all strata except the most northerly Admiralty Inlet Stratum, which appears to be important to murrelets year-round. Depending on the year, non-breeding season densities were nearly the same or higher than breeding season densities indicate that murrelets were not moving into the relatively protected inner marine waters of Puget Sound from more outer coastal environments during the non-breeding season as predicted.
斑海雀（Brachyramphus marmoratus）在美国华盛顿州、俄勒冈州和加利福尼亚州被归类为濒危物种，因为其数量下降、繁殖栖息地丧失和其他因素。迄今为止，种群评估主要集中在繁殖季节的海上调查。因此，关于该物种在非繁殖季节的分布、丰度和种群趋势的信息很少，因为斑海雀在非繁殖季节只在海洋环境中发现。为了解决这一信息需求，我们评估了 8 年来，在斑海雀繁殖季节调查显示种群下降 20 年的部分地区，即美国华盛顿州普吉特湾，非繁殖季节海上斑海雀数量模式和种群趋势。这使我们能够评估非繁殖季节的种群趋势是否与繁殖季节的观察结果一致，表明存在区域性全年保护问题，并确定重要的越冬区（高丰度区）。我们将非繁殖季节的丰度信息与繁殖季节的信息相结合，以评估全年的丰度模式。这使我们能够检验这样一个预测，即斑海雀在非繁殖季节从恶劣的外海栖息地迁徙到普吉特湾相对受保护的内海水域，以换羽和越冬。与繁殖季节的趋势类似，我们观察到整个非繁殖期（9 月和 4 月）的斑海雀密度急剧下降，秋季和初冬（9 月下旬至 12 月）调查窗口下降最为明显，此时鸟类换羽，早春繁殖前（3 月至 4 月）。尽管有这些下降，但在冬季中期（1 月至 2 月），当整体密度较低时，斑海雀的密度基本上没有变化。普吉特湾斑海雀的密度呈现出很强的南北梯度，北部密度较高，南部密度较低；普吉特湾中部基本上没有斑海雀。除了普吉特湾中部之外，其他地层的密度随季节变化，9 月至 12 月之间鸟类在各地层之间分布均匀，但在冬末/早春时期（1 月至 4 月），除了最北部的阿德默勒尔蒂群岛入口地层外，各地层基本上都没有斑海雀，阿德默勒尔蒂群岛入口地层似乎全年对斑海雀都很重要。根据不同年份，非繁殖季节的密度与繁殖季节的密度几乎相同或更高，表明斑海雀并没有像预测的那样，在非繁殖季节从更靠外的沿海环境迁徙到普吉特湾相对受保护的内海水域。
