Highly migratory shorebirds are among the fastest declining avian guilds, so determining causes of mortality is critically important for their conservation. Most of these species depend on a specific geographic arrangement of suitable sites that reliably provide resources needed to fuel physiologically demanding life histories. Long-term mark-resight projects allow researchers to investigate specific potential sources of variation in demographic rates between populations. Red Knots (Calidris canutus) occur in three relatively distinct regions across the northern Gulf of Mexico, and two of these areas have been experiencing episodic harmful algal blooms (red tide) with increased frequency in recent decades. Since knots are mostly molluscivorous during the nonbreeding season in the Gulf, they are potentially exposed to red tide toxins at high concentrations via their filter-feeding prey. We used long-term mark-resight data from Texas, Louisiana, and Florida (USA) to estimate apparent survival, and to assess the effects of red tides on survival of Red Knots. We also assessed effects of tracking devices deployed in conjunction with the projects over the years. While overall apparent annual survival rates were similar across the three locations (0.768 – 0.819), several red tide events were associated with catastrophically low seasonal (fall) survival in Florida (as low as 0.492) and Texas (as low as 0.510). Leg-mounted geolocators, but not temporary glued-on VHF tags, were associated with a reduction in apparent survival (~8%/year). Movement of knots between the three areas was rare and site fidelity is known to be high. Harmful algal blooms are predicted to increase in frequency and severity with climate change and increased anthropogenic degradation of coastal habitats, which may further endanger these as well as other shorebird populations around the world.

中文翻译：

---

墨西哥湾北部红滨鹬的生存

高度迁徙的滨鸟是数量下降最快的鸟类之一，因此确定死亡原因对于保护它们至关重要。这些物种中的大多数依赖于合适地点的特定地理布置，这些地点可靠地提供了满足生理要求的生活史所需的资源。长期标记重新审视项目使研究人员能够调查人群之间人口统计比率变化的特定潜在来源。红结（鲫鱼）发生在墨西哥湾北部三个相对不同的地区，其中两个地区近几十年来经历了偶发性有害藻华（赤潮），且频率不断增加。由于滨海结在海湾的非繁殖季节大多是软体动物，因此它们可能通过滤食性猎物接触到高浓度的赤潮毒素。我们使用德克萨斯州、路易斯安那州和佛罗里达州（美国）的长期标记重新观测数据来估计表观生存率，并评估赤潮对红滨鹬生存的影响。我们还评估了多年来与项目一起部署的跟踪设备的效果。虽然这三个地点的总体表观年生存率相似（0.768 – 0.819），但佛罗里达州（低至 0.492）和德克萨斯州（低至 0.510）的几次赤潮事件与灾难性的低季节性（秋季）生存率有关。安装在腿上的地理定位器（而不是临时粘贴的 VHF 标签）与表观生存率下降有关（约 8%/年）。三个区域之间的结运动很少，并且场地保真度很高。预计随着气候变化和沿海栖息地人为退化的加剧，有害藻华的频率和严重程度将会增加，这可能会进一步危及这些以及世界各地的其他滨鸟种群。