Red Knot observations on the Virginia Coast, 2007-2019

Red Knot observations on the Virginia Coast, 2007-2019 Understanding factors that influence a species' distribution and abundance across the annual cycle is required for range-wide conservation. Thousands of imperiled red knots (Calidris cantus rufa) stop on Virginia's barrier islands each year to replenish fat during spring migration. We investigated the variation in red knot presence and flock size, the effects of prey on this variation, and factors influencing prey abundance on Virginia's barrier islands. We counted red knots and collected potential prey samples at randomly selected sites from 2007 - 2018 during a two-week period during early and peak migration. Core samples contained crustaceans (Orders Amphipoda and Calanoida), blue mussels (Mytilus edulis), coquina clams (Donax variabilis), and miscellaneous prey (horseshoe crab eggs (Limulus polyphemus), angel wing clams (Cyrtopleura costata), and other organisms (e.g., insect larvae, snails, worms)). Estimated red knot numbers in Virginia during peak migration were highest in 2012 (11,959) and lowest in 2014 (2,857; 12-year peak migration x̄ = 7,175, SD = 2,869). Red knot and prey numbers varied across sampling periods and substrates (i.e., peat and sand). Red knots generally used sites with more prey. Miscellaneous prey (x̄ = 18.85/core sample, SE = 0.88) influenced red knot presence at a site early in migration, when we only sampled on peat banks. Coquina clams (x̄ = 11/core sample, SE = 0.30) and blue mussels (x̄ = 0.94/core sample, SE = 0.04) affected red knot presence at a site during peak migration, when we sampled both substrates. Few relationships between prey and red knot flock size existed, suggesting that other unmeasured factors determined red knot numbers at occupied sites. Tide and mean daily water temperature affected prey abundance. Maximizing the diversity, availability, and abundance of prey for red knots on barrier islands requires management that encourages the presence of both sand and peat bank intertidal habitats.

弗吉尼亚海岸红腹滨鹬（Red Knot）观测数据（2007-2019年）
要实现物种的全域保护，需明确年度周期内影响其分布与丰度的关键因素。每年春季迁徙期间，数千只濒危红腹滨鹬（学名：Calidris cantus rufa）会在弗吉尼亚的堰洲岛上停歇，以补充脂肪储备。本研究旨在探究弗吉尼亚堰洲岛上红腹滨鹬的出现频率与种群规模变化、猎物对这些变化的影响，以及影响猎物丰度的关键因素。2007至2018年间，我们在迁徙初期与高峰期的两周内，于随机选取的站点开展红腹滨鹬计数，并采集潜在猎物样本。核心样本包含甲壳类动物（端足目Amphipoda、哲水蚤目Calanoida）、紫贻贝（Mytilus edulis）、可变斧蛤（Donax variabilis），以及其他杂类猎物（如美洲鲎卵Limulus polyphemus、天使翼蛤Cyrtopleura costata，及昆虫幼虫、蜗牛、蠕虫等生物）。弗吉尼亚地区迁徙高峰期红腹滨鹬的估算数量在2012年达到最高（11,959只），2014年最低（2,857只）；12年间高峰期的均值为7,175只，标准差SD为2,869只。红腹滨鹬与猎物数量在不同采样时段及基质（即泥炭与沙质）间存在差异。红腹滨鹬通常偏好猎物更丰富的站点。迁徙初期仅在泥炭滩采样时，杂类猎物（均值：18.85个/核心样本，标准误SE：0.88）对红腹滨鹬的站点出现率有显著影响；迁徙高峰期同时采样两种基质时，可变斧蛤（均值：11个/核心样本，标准误SE：0.30）与紫贻贝（均值：0.94个/核心样本，标准误SE：0.04）对红腹滨鹬的站点出现率产生影响。猎物与红腹滨鹬种群规模间的关联较少，这表明尚有其他未测量因素决定了已占据站点的红腹滨鹬数量。潮汐与日均水温会影响猎物丰度。若要最大化堰洲岛上红腹滨鹬猎物的多样性、可获得性与丰度，需采取管理措施以保护沙质与泥炭滩两种潮间带栖息地。