Factors that affect migratory Western Atlantic red knots (Calidris canutus rufa) and their prey during spring staging on Virginia’s barrier islands

• Main Authors: Heller, Erin L., Karpanty, Sarah M., Cohen, Jonahan B., Catlin, Daniel H., Ritter, Sharon J., Truitt, Barry R., Fraser, James D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: PLOS 2022
• Subjects: Barrier Islands; Calidris canutus; Red Knot
• Online Access: http://hdl.handle.net/10919/114543; https://doi.org/10.1371/journal.pone.0270224

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 Virginias 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 Virginias barrier islands. We counted red knots and collected potential prey samples at randomly selected sites from 20072018 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 peak counts in Virginia during 2127 May were highest in 2012 (11,959) and lowest in 2014 (2,857; 12-year peak migration x = 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 (x = 2401.00/m², SE = 169.16) influenced red knot presence at a site early in migration, when we only sampled on peat banks. Coquina clams (x = 1383.54/m², SE = 125.32) and blue mussels (x = 777.91/m², SE = 259.31) 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. This research was supported by the National Marine Fisheries Service of the National Oceanic ...