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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. [ABSTRACT FROM AUTHOR]

The largest aggregation of spawning American horseshoe crabs in the world occurs in Delaware Bay and supports one of the largest concentrations of shorebirds in the western hemisphere where the birds feed on horseshoe crab eggs during migration. Unregulated harvest in the 1990s is associated with the decline of shorebird populations using the bay, but corresponding baseline information on the horseshoe crab egg food supply that supported peak shorebird populations has been lacking.Past and current measurements of horseshoe crab eggs in the bay indicate that abundance in the 1980s was an order of magnitude greater (x̄ = 156,600/m2) than present‐day estimates (2015–2021 x̄ = 10,243/m2). An additional egg prevalence index, which characterizes the timing and magnitude of horseshoe crab egg output, revealed a similar pattern of higher prevalence in the 1980s (0.89, 95% confidence interval 0.81–0.94) compared with the recent 2015–2021 interval (0.52, 95% confidence interval 0.43–0.60).Declines of egg and shorebird abundance occurred shortly after horseshoe crab harvest reached its peak. Red knot aerial survey counts have stabilized at 30% of the baseline population while ruddy turnstone counts are 40% of baseline estimates. Initially these species were evenly distributed between the New Jersey and Delaware coasts but both species have trended toward predominately occupying New Jersey beaches.A lack of recovery of horseshoe crab egg and shorebird abundance suggests that horseshoe crab harvest management has stabilized populations but progress toward population recovery has been limited. Impacts from bycatch, the pharmaceutical industry and other potential population impacts must be better quantified and mitigated, if necessary, to promote the recovery of horseshoe crab populations. Measurements of horseshoe egg prevalence and abundance are essential metrics for tracking the progress toward management goals for improving shorebird habitat quality. [ABSTRACT FROM AUTHOR]

Surveys of the North American race of the Red Knot (Calidris canutus rufa) on its main wintering areas on the coasts of Patagonia and Tierra del Fuego (Argentina and Chile) showed a dramatic decline in the wintering population: totals in 2003 were about 30 000 compared to 67 500 in the mid-1980s. Numbers at the principal wintering site, Bahia Lomas, fell by approximately 50%, from 45 300 in 2000 to 22 000-25 000 in 2002-2003. Numbers at peripheral sites on the coast of Patagonia declined dramatically, decreasing 98% compared to numbers in the mid-1980s. The results showed that declines at core sites did not result from birds moving to other places within the known wintering (or other) areas, but reflected a general population decline, with most birds now restricted to key sites in Tierra del Fuego. This phenomenon may explain why long-term declines noted elsewhere have only recently become apparent at key wintering areas. Possible reasons for the declines are discussed. Banding studies in Delaware Bay have shown that in recent years an increasing proportion of Red Knots is unable to gain sufficient weight for migration to the breeding grounds. This is likely due to reductions in their main food resource, eggs of the horseshoe crab Limulus polyphemus. The resulting increase in mortality could account for the magnitude and severity of the declines we observed. Key words: conservation, declines, population, Red Knot, shorebirds.

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The movements and distribution of 65 radio tagged red knots on Delaware Bay from May to June 2004 and related movements to the distribution and abundance of horseshoe crab eggs and to other habitat characteristics are studied. The findings are found to be consistent with the hypothesis that the abundance of horseshoe crab eggs on sandy beaches is driving movement and distribution of red knots and that there is little alternative food during the majority stopover in Delaware Bay.

Wild birds have been implicated in the emergence of human and livestock influenza. The successful prediction of viral spread and disease emergence, as well as formulation of preparedness plans have been hampered by a critical lack of knowledge of viral movements between different host populations. The patterns of viral spread and subsequent risk posed by wild bird viruses therefore remain unpredictable. Here we analyze genomic data, including 287 newly sequenced avian influenza A virus (AIV) samples isolated over a 34-year period of continuous systematic surveillance of North American migratory birds. We use a Bayesian statistical framework to test hypotheses of viral migration, population structure and patterns of genetic reassortment. Our results reveal that despite the high prevalence of Charadriiformes infected in Delaware Bay this host population does not appear to significantly contribute to the North American AIV diversity sampled in Anseriformes. In contrast, influenza viruses sampled from Anseriformes in Alberta are representative of the AIV diversity circulating in North American Anseriformes. While AIV may be restricted to specific migratory flyways over short time frames, our large-scale analysis showed that the long-term persistence of AIV was independent of bird flyways with migration between populations throughout North America. Analysis of long-term surveillance data provides vital insights to develop appropriately informed predictive models critical for pandemic preparedness and livestock protection. [ABSTRACT FROM AUTHOR]

The article presents a study focusing on migration and over-wintering of Red Knot birds along the Atlantic Coast of the U.S. The study reflected the variation in Knots' migration patterns which include four birds along the U.S. Atlantic coast and rest to the Caribbean islands and South America. It was also found that Knots spent 58 to 75 days in Monomoy Refuge before migrating to the south in November.

The article presents a study which examined temporal avian influenza virus (AIV) prevalence trends in four Charadriiformes species, namely, Ruddy turnstones, Red knots, Sanderlings and Laughing gulls during the spring migratory stopover at Delaware Bay. Serial cross-sectional data from 2000 through 2008 and generalized linear and additive models were utilized. Only Sanderlings exhibited dynamical changes in AIV prevalence over the stopover period.

Adaptive management requires that predictive models be explicit and transparent to improve decisions by comparing management actions, directing further research and monitoring, and facilitating learning. The rufa subspecies of red knots ( Calidris canutus rufa), which has recently exhibited steep population declines, relies on horseshoe crab ( Limulus polyphemus) eggs as their primary food source during stopover in Delaware Bay during spring migration. We present a model with two different parameterizations for use in the adaptive management of horseshoe crab harvests in the Delaware Bay that links red knot mass gain, annual survival, and fecundity to horseshoe crab dynamics. The models reflect prevailing hypotheses regarding ecological links between these two species. When reported crab harvest from 1998 to 2008 was applied, projections corresponded to the observed red knot population abundances depending on strengths of the demographic relationship between these species. We compared different simulated horseshoe crab harvest strategies to evaluate whether, given this model, horseshoe crab harvest management can affect red knot conservation and found that restricting harvest can benefit red knot populations. Our model is the first to explicitly and quantitatively link these two species and will be used within an adaptive management framework to manage the Delaware Bay system and learn more about the specific nature of the linkage between the two species. [ABSTRACT FROM AUTHOR]

For long-distance migrants, such as many of the shorebirds, understanding the demographic implications of behavioural strategies adopted by individuals is key to understanding how environmental change will affect populations. Stable isotopes have been used in the terrestrial environment to infer migratory strategies of birds but rarely in marine or estuarine systems. Here, we show that the stable isotope ratios of carbon and nitrogen in flight feathers can be used to identify at least three discrete wintering areas of the Red Knot Calidris canutus on the eastern seaboard of the Americas, ranging from southeastern USA to Patagonia and Tierra del Fuego. In spring, birds migrate northwards via Delaware Bay, in the northeastern USA, the last stopping point before arrival in Arctic breeding areas, where they fatten up on eggs of spawning Horseshoe Crabs Limulus polyphemus. The isotope ratios of feather samples taken from birds caught in the Bay during May 2003 were compared with feathers obtained from known wintering areas in Florida (USA), Bahia Lomas (Chile) and Rio Grande (Argentina). In May 2003, 30% of birds passing through the Bay had Florida-type ‘signatures’, 58% were Bahia Lomas-type, 6% were Rio Grande-type and 7% were unclassified. Some of the southern wintering birds had started moulting flight feathers in northern areas, suspended this, and then finished their moult in the wintering areas, whereas others flew straight to the wintering areas before commencing moult. This study shows that stable isotopes can be used to infer migratory strategies of coastal-feeding shorebirds and provides the basis for identifying the moult strategy and wintering areas of birds passing through Delaware Bay. Coupled with banding and marking birds as individuals, stable isotopes provide a powerful tool for estimating population-specific demographic parameters and, in this case, further our understanding of the migration systems of the declining Nearctic populations of Red Knot. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article “Effects of Horseshoe Crab Harvest in Delaware Bay on Red Knots: Are Harvest Restrictions Working?,” by L.J. Niles et al. in a 2009 issue. A response by Lawrence J. Niles and his colleagues is appended.

Decision analytic approaches have been widely recommended as well suited to solving disputed and ecologically complex natural resource management problems with multiple objectives and high uncertainty. However, the difference between theory and practice is substantial, as there are very few actual resource management programs that represent formal applications of decision analysis. We applied the process of structured decision making to Atlantic horseshoe crab harvest decisions in the Delaware Bay region to develop a multispecies adaptive management (AM) plan, which is currently being implemented. Horseshoe crab harvest has been a controversial management issue since the late 1990s. A largely unregulated horseshoe crab harvest caused a decline in crab spawning abundance. That decline coincided with a major decline in migratory shorebird populations that consume horseshoe crab eggs on the sandy beaches of Delaware Bay during spring migration. Our approach incorporated multiple stakeholders, including fishery and shorebird conservation advocates, to account for diverse management objectives and varied opinions on ecosystem function. Through consensus building, we devised an objective statement and quantitative objective function to evaluate alternative crab harvest policies. We developed a set of competing ecological models accounting for the leading hypotheses on the interaction between shorebirds and horseshoe crabs. The models were initially weighted based on stakeholder confidence in these hypotheses, but weights will be adjusted based on monitoring and Bayesian model weight updating. These models were used together to predict the effects of management actions on the crab and shorebird populations. Finally, we used a dynamic optimization routine to identify the state dependent optimal harvest policy for horseshoe crabs, given the possible actions, the stated objectives and our competing hypotheses about system function. The AM plan was reviewed, accepted and implemented by the Atlantic States Marine Fisheries Commission in 2012 and 2013. While disagreements among stakeholders persist, structured decision making enabled unprecedented progress towards a transparent and consensus driven management plan for crabs and shorebirds in Delaware Bay. [ABSTRACT FROM AUTHOR]

Delaware (DE) Bay, in the northeastern USA, has long been recognized as a hotspot for avian influenza A virus (IAV); every spring, this coastal region serves as a brief stopover site for thousands of long-distance migrating shorebirds, en route to breeding grounds in the Arctic. During these stopovers, IAV has been consistently recovered from ruddy turnstones ( Arenaria interpres ) that are likely to become infected as they feed by probing sand and cobble in search of food. In May 2010-2012, we successfully isolated 19 IAV from environmental samples (sand, n  = 18; horseshoe crab eggs, n  = 1) obtained from DE Bay sites. Two of these viruses were subjected to laboratory conditions similar to those in the DE Bay spring-time environment, and remained infectious for 7 days. Here, through the recovery of IAV from environmental samples, temperature monitoring at and below the sand surface and simulated laboratory trials, we provide evidence that the beach environment may enable localized transmission and short-term maintenance of IAV in this unique ecosystem., Competing Interests: We declare we have no competing interests.

Understanding temporal changes in contaminant levels in coastal environments requires comparing levels of contaminants from the same species from different time periods, particularly if species are declining. Several species of shorebirds migrating through Delaware Bay have declined from the 1980s to the present. To evaluate some contaminants as cause for the declines, we examine levels of mercury, lead, cadmium, arsenic, chromium and selenium in feathers of red knot ( Calidris canutus , N = 46 individuals), semipalmated sandpiper ( Calidris pusilla , N = 70) and sanderling ( Calidris alba , N = 32) migrating through Delaware Bay, New Jersey, USA, from 1991 to 1992 ( N = 40), 1995 ( N = 28), and 2011-2012 ( N = 80) to determine if levels have changed. We found: (1) arsenic, chromium, and lead increased in red knot and decreased in semipalmated sandpiper; (2) cadmium decreased in semipalmated sandpipers; (3) mercury decreased in red knot and sanderlings; (4) selenium decreased in red knot and increased in semipalmated sandpipers. In 2011/2012 there were significant interspecific differences for arsenic, mercury and selenium. Except for selenium, the element levels were well below levels reported for feathers of other species. The levels in feathers in red knots, sanderling, and semipalmated sandpipers from Delaware Bay in 2011/2012 were well below levels in feathers that are associated with effect levels, except for selenium. Selenium levels ranged from 3.0 µg·g -1 dry weight to 5.8 µg·g -1 (semipalmated sandpiper), within the range known to cause adverse effects, suggesting the need for further examination of selenium levels in birds. The levels of all elements were well below those reported for other marine species, except for selenium, which was near levels suggesting possible toxic effects.