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25 results for “red knot”
Red knot occurrence, prey density, island morphology, and climate change in the Virginia Barrier Islands (2009-2023)
Global climate change is reshaping dynamic coastal ecosystems, with uncertain consequences for migratory shorebirds such as the federally threatened red knot (Calidris canutus rufa) that rely on coastal staging sites during migration. Understanding how sea-level rise and changing climate drivers affect red knot foraging ecology is critical for informing conservation and management at coastal staging sites. We integrated long-term biological, geomorphological, and climatological data to examine the direct and indirect pathways influencing red knots and their prey at intertidal foraging sites on the Virginia Barrier Islands during spring migration (May 21 - 28, 2009-2023). Using piecewise structural equation modeling, we tested hypothesized two causal networks linking 1) red knot occurrence and 2) densities of their main invertebrate prey to habitat characteristics, island morphology, geomorphic change, and climate drivers of ecosystem change. Red knots were indirectly affected by geomorphic change and climate drivers through bottom-up effects on invertebrate communities mediated by island morphology. Accelerated shoreline change narrowed islands, reducing invertebrate density and richness and indirectly decreasing red knot occurrence. Storms interacted with global climate oscillations to drive erosion or accretion of beaches, with variable effects on invertebrate density and red knot occurrence. Invertebrate responses were taxon-specific: shoreline change directly increased blue mussel density but indirectly reduced coquina clam and crustacean densities by narrowing island width, while storms impacts on crustacean density were mediated by beach width. Our findings suggest that accelerated ecosystem change under future climate scenarios may alter foraging conditions for red knots and other migratory shorebirds in the Virginia Barrier Islands, with broader implications for long-term population resilience.
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 a
Taxonomic Composition of Red Knot Fecal Samples on the Virginia Coast
Taxonomic Composition of Red Knot Fecal Samples on the Virginia Coast Understanding which prey birds use and how prey selection is related to prey availability is important to understanding avian ecology and for conservation planning. Abundant prey at stopovers during migration is a key to shorebird survival and breeding success. We determined which prey were available to foraging red knots (Calidris canutus rufa) using Virginia's barrier islands during spring migration by collecting substrate core samples containing prey on sand and peat substrates in May 2017 - 2019. We also collected red knot feces during the same period and used fecal DNA metabarcoding to determine which invertebrates red knots consumed. We used compositional analysis to determine which prey red knots selected on these islands. Crustaceans (Orders Amphipoda and Calanoida) were the most abundant prey on both sand and peat. Red knots consumed bivalves (Orders Venerida and Mytiloida), crustaceans (Orders Amphipoda and Calanoida), and insect larvae (Order Diptera). Red knots selected bivalves over non-bivalve prey, though non-bivalve prey may still be an important portion of the total caloric intake on Virginia's stopover, given their abundance and use. It is important that coastal conservation practices in the Western Mid-Atlantic stopover region continue to be designed to promote natural barrier island movement which leads to the formation of the peat banks used by many prey.
Data from: Evaluating staging habitat quality to advance the conservation of a declining migratory shorebird, Red Knot Calidris canutus
<p>Identifying where and when population "bottlenecks" occur is critical to the conservation of migratory species, many of which are declining precipitously worldwide. Especially challenging is the evaluation of changes to staging sites. These sites are indispensable links in the migratory cycle but are typically used only briefly.</p> <p>We devised a field-based approach to assess the quality and carrying capacity of a critical staging site in Nanpu, China, for the declining, migratory Red Knot (Calidris canutus rogersi & C. c. piersmai) during northward migration. The Nanpu tidal flat supports 50,000-100,000 Red Knots annually, and while there, the knots feed almost exclusively on the bivalve Potamocorbula laevis. We simultaneously monitored changes in the abundance of Red Knots and bivalves across the entire staging site in spring 2018.</p> <p>After taking into account potential competition with other shorebird species, we estimated that the Nanpu tidal flat was capable of supporting approximately 1.46-1.70 times the current observed level of usage of the site by Red Knots, and therefore is operating below, but close, to carrying capacity with respect to food resources for Red Knots. This result suggests that any further development of this site could harm the EAAF Red Knot population.</p> <p>Synthesis and applications: Quantitative monitoring and evaluation of habitat quality of staging sites are essential to successfully conserve declining migratory species. In particular, researchers and conservation practitioners should incorporate both population size and staging duration in order to more accurately assess the importance of different sites and to quantify how changes in staging habitat quality may translate into changes in migrant population sizes at both local and global scales.</p>
Data for: Resource landscapes explain contrasting patterns of aggregation and site fidelity by red knots at two wintering sites
<p>This repository contains data for the paper: Oudman et al. 2018. Resource landscapes explain contrasting patterns of aggregation and site fidelity by red knots at two wintering sites. <em>Movement Ecology</em> 6(14) 1-12. https://doi.org/10.1186/s40462-018-0142-4.</p> <p>Please cite the original publication when using this data.</p>
Evidence for personality development: juvenile red knots vary more in diet and exploratory behaviour than adults
<p>Evidence is accumulating that foraging behaviour and diet link to personality traits, yet little is known about how these associations emerge during development. It is expected that behaviour becomes more consistent with age, and thus experience. We compared exploratory behaviour and diet variances of juvenile and adult red knots shortly after migration to intertidal mudflats from tundra breeding grounds. By identifying the timing of the switch from tundra to marine isotopic signatures, we were also able to ask whether juveniles that arrived earlier were more consistent in exploration behaviour. We found that juveniles had a more diverse diet than adults, and that juveniles were less repeatable in exploration than adults. While juveniles had larger within-individual variance, among-individual variance was similar between age groups. Juveniles that arrived earlier did not vary more in exploratory behaviour compared to those that arrived later, suggesting that consistency in exploration was developed over a longer period than the four weeks of our study. Our findings suggests that after initial exploration of a novel habitat, juveniles likely try-out foraging techniques which later develop into consistent behaviours that differ among individuals. This study illuminates how personality can develop with experience in a free-living animal.</p>
Data from: Evaluating staging habitat quality to advance the conservation of a declining migratory shorebird, Red Knot Calidris canutus
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Evidence for personality development: juvenile red knots vary more in diet and exploratory behaviour than adults
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Global flyway evolution in red knots Calidris canutus and genetic evidence for a Nearctic refugium
<p>Present-day ecology and population structure are the legacies of past climate and habitat perturbations, and this is particularly true for species that are widely distributed at high latitudes. The red knot, <em>Calidris canutus</em>, is an arctic-breeding, long-distance migratory shorebird with six recognized subspecies defined by differences in morphology, migration behavior, and annual-cycle phenology, in a global distribution thought to have arisen just since the Last Glacial Maximum (LGM). We used nextRAD sequencing of 10,881 single-nucleotide polymorphisms (SNPs) to assess the neutral genetic structure and phylogeographic history of 172 red knots representing all known global breeding populations. Using population genetics approaches, including model-based scenario-testing in an approximate Bayesian computation (ABC) framework, we infer that red knots derive from two main lineages that diverged ca. 34,000 years ago, and thus most likely persisted at the LGM in both Palearctic and Nearctic refugia, followed by at least two instances of secondary contact and admixture. Within two Beringian subspecies (<em>C. c. roselaari</em> and <em>rogersi</em>), we detected previously unknown genetic structure among sub-populations sharing a migratory flyway, reflecting additional complexity in the phylogeographic history of the region. Conversely, we found very weak genetic differentiation between two Nearctic populations (<em>rufa</em> and <em>islandica</em>) with clearly divergent migratory phenotypes and little or no apparent contact throughout the annual cycle. Together, these results suggest that relative gene flow among migratory populations reflects a complex interplay of historical, geographical, and ecological factors.</p>
Genetic structure in the nonbreeding range of rufa Red Knots suggests distinct Arctic breeding populations
<p>An understanding of the migratory connectivity between breeding and nonbreeding areas is fundamental to the management of long-distance migrants under pressure from habitat change along their flyways. Here we describe evidence for genetic structure within the nonbreeding range of the endangered Arctic-Canadian rufa subspecies of Red Knots (Calidris canutus). Using blood and tissue samples from the major nonbreeding regions in Argentina (Tierra del Fuego and Río Negro), northern Brazil (Maranhão), and southeastern USA (Florida), we estimated genetic structure in 514 amplified fragment length polymorphism (AFLP) loci, applying cluster assignment analyses in DAPC, assignPOP, and STRUCTURE. Using a priori location information, individuals could be correctly re-assigned to their nonbreeding regions, which validated that the assignment accuracy of the data was sufficient. Without using a priori location information, we detected 3–5 genotype clusters, and posterior assignment probabilities of samples to these genotype clusters varied among the three regions. Lastly a chi-square test confirmed that allele frequencies varied significantly among nonbreeding regions, rejecting the hypothesis that samples were drawn from a single gene pool. Our findings hint at undescribed structure within the Red Knot rufa breeding range in the Canadian Arctic and indicate that each rufa nonbreeding area in this study hosts a different subsample of these breeding populations. The observation that nonbreeding sites of rufa Red Knots contain different genetic pools argues for separate conservation management of these sites.</p>
Future sea level rise in northwest Mexico is projected to decrease the distribution and habitat quality of the endangered Calidris canutus roselaari (Red Knot)
<p>Sea level rise (SLR) is one of the most unequivocal consequences of climate change, yet the implications for shorebirds and their coastal habitats is not well understood, especially outside of the north temperate zone. Here, we show that by the year 2050, SLR has the potential to cause significant habitat loss and reduce the quality of the remaining coastal wetlands in Northwest Mexico—one of the most important regions for Nearctic breeding migratory shorebirds. Specifically, we used species distribution modelling and a moderate SLR static inundation scenario to assess the effects of future SLR on coastal wetlands in Northwest Mexico and the potential distribution of <em>Calidris canutus roselaari </em>(Red Knot), a threatened long-distance migratory shorebird. Our results suggest that under a moderate SLR scenario, 55% of the current coastal wetland extent in northwest Mexico will be at risk of permanent submergence by 2050, and the high-quality habitat areas that remain will be 20% less suitable for <em>C. c. roselaari</em>. What is more, 8 out of the 10 wetlands currently supporting the largest numbers of <em>C. c. roselaari</em> are predicted to lose — on average — 17.8% of their highly suitable habitat areas, with two sites completely losing all their highly suitable habitat. In combination with increasing levels of coastal development and anthropogenic disturbance in Northwest Mexico, these predicted changes suggest that the potential future distribution of <em>C. c. roselaari</em> (and other shorebirds) will likely contract, exacerbating their ongoing population declines. Our results also make clear that SLR will likely have profound effects on ecosystems outside the north temperate zones, providing a clarion call to natural resource managers. Urgent action is required to begin securing sufficient space to accommodate the natural capacity of wetlands to migrate inland and implement local-scale solutions that strengthen the resilience of wetlands and human populations to SLR.</p>
Genetic structure in the nonbreeding range of rufa Red Knots suggests distinct Arctic breeding populations
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Future sea level rise in northwest Mexico is projected to decrease the distribution and habitat quality of the endangered Calidris canutus roselaari (Red Knot)
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Global flyway evolution in red knots Calidris canutus and genetic evidence for a Nearctic refugium
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Data from: A red knot as a black swan: how a single bird shows navigational abilities during repeat crossings of the Greenland Icecap
<p>Despite the wealth of studies on seasonal movements of birds between southern nonbreeding locations and High Arctic breeding locations, the key mechanisms of navigation during these migrations remain elusive. A flight along the shortest possible route between pairs of points on a sphere ('orthodrome') requires a bird to be able to assess its current location in relation to its migration goal and to make continuous adjustment of heading to reach that goal. Alternatively, birds may navigate along a vector with a fixed orientation ('loxodrome') based on magnetic and/or celestial compass mechanisms. Compass navigation is considered especially challenging for summer migrations in Polar regions, as continuous daylight and complexity in the geomagnetic field may complicate the use of both celestial and magnetic compasses here. We examine the possible use of orientation mechanisms during migratory flights across the Greenland Icecap. Using a novel 2 g solar-powered satellite transmitter, we documented the flight paths travelled by a female red knot (<i>Calidris canutus islandica</i>) during two northward and two southward migrations. The geometry of the paths suggests that red knots can migrate across the Greenland Icecap along the shortest-, orthodrome-like, path instead of the previously suggested loxodrome path. This particular bird's ability to return to locations visited in a previous year, together with its sudden course changes (which would be appropriate responses to ambient wind fields), suggest a map sense that enables red knots to determine location, so that they can tailor their route depending on local conditions.</p>
Data from: Accounting for heterogeneity when estimating stopover duration, timing and population size of red knots along the Luannan Coast of Bohai Bay, China
1. To successfully perform their long-distance migrations, migratory birds require sites along their migratory routes to rest and refuel. Monitoring the use of so-called stopover and staging sites provides insights into (1) the timing of migration and (2) the importance of a site for migratory bird populations. A recently developed Bayesian superpopulation model that integrates mark-recapture data and ring density data enabled the estimation of stopover timing, duration and population size. Yet, this model did not account for heterogeneity in encounter (p) and staying (ϕ) probabilities. 2. Here we extended the integrated superpopulation model by implementing finite mixtures to account for heterogeneity in p and ϕ. We used simulations and real data on red knots Calidris canutus staging in Bohai Bay, China, during spring migration to (1) show the importance of accounting for heterogeneity in encounter and staying probabilities to get unbiased estimates of stopover timing, duration and numbers of migratory birds at staging sites and (2) get accurate stopover parameter estimates for a migratory bird species at a key staging site that is threatened by habitat destruction. 3. Our simulations confirmed that heterogeneity in p affected stopover parameter estimates more than heterogeneity in ϕ. Bias was particularly severe when most birds had both low ϕ and p. Bias was largest for population size, intermediate for stopover duration and negligible for stopover timing. 4. 50,000-100,000 red knots were estimated to annually stop for 5-9 days in Bohai Bay between 10 and 30 May. This shows the key importance of this staging site for this declining species. There were no clear changes in stopover parameters over time. 5. Our study shows the importance of accounting for heterogeneity in both encounter and staying probabilities for accurately estimating stopover duration and population size and provides an appropriate modelling framework.
Exploration speed in captivity predicts foraging tactics and diet in free-living red knots
<p>Variation in foraging tactics and diet are usually attributed to differences in morphology, experience, and prey availability. Recently, consistent individual differences in behaviour (personality) have been shown to be associated with foraging strategies. Bolder or more exploratory individuals are predicted to have a faster pace-of-life and offset the costs of moving more or in risky areas, with higher energetic gains by encountering profitable foraging opportunities and prey. However, the relationship between personality, foraging, and diet is poorly understood.</p> <p>We investigated how exploratory behaviour in red knots (<em>Calidris canutus</em><i>) </i>is associated with foraging tactics and diet by combining laboratory experiments, field observations, and stable isotope analysis. First, we developed a mobile experimental arena to measure exploration speed in controlled settings. We validated the method by repeated testing of individuals over time and contexts. This setup allowed us to measure exploratory personality at the field site, eliminating the need to bring birds into captivity for long periods of time. After releasing birds within days of their capture, we asked whether exploration speed was associated with differences in foraging tactics and diet in the wild.</p> <p>We found that tactile foraging red knots mainly caught hard-shelled prey that are buried in the sediment, whereas visual foraging knots only captured soft preys located close to or on the surface. We also found that faster explorers showed a higher percentage of visual foraging than slower explorers. By contrast, morphology (bill length and gizzard size) had no significant effect on foraging tactics. Diet analysis based on δ15N and δ13C stable isotope values of plasma and red blood cells confirmed our field observations with slower explorers mainly consumed hard-shelled prey while faster explorers consumed more soft than hard-shelled prey.</p> <p>Our results show that foraging tactics and diet are associated with a personality trait, independent of morphological differences. We discuss how consistent behaviour might develop early in life through positive feedbacks between foraging tactics, prey type, and foraging efficiency.</p>
Data from: A red knot as a black swan: how a single bird shows navigational abilities during repeat crossings of the Greenland Icecap
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Data from: Accounting for heterogeneity when estimating stopover duration, timing and population size of red knots along the Luannan Coast of Bohai Bay, China
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Data from: An experimental test of state-behaviour feedbacks: gizzard mass and foraging behaviour in red knots
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Allen Brain Atlas
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