Migratory Shorebirds Research Articles

Habitat Use of Migratory Shorebirds on the Coastline of Deli Serdang Regency, North Sumatra Province

Mangrove forests an intertidal mudflat in the eastern coastal region of Deli Serdang are important habitats for migratory shorebirds. Land-use change and forest conversion threaten this important stopover point for migrating species. The lack of data and information of shorebirds habitats in this area limits conservation efforts and further threatens the survival of these species. The objective of this study is to investigate trends in habitat use by migratory shorebirds. Field work was conducted during migration season starting from October 2014 until April 2015. The presence of migratory shorebirds was assessed using binoculars and a monocular. Scan sampling was used to describe habitat use by shorebirds. The difference in behaviour among habitat was analyzed using analysis of variance. There were 30 species of shorebirds distributed across seven different habitat types in our study area. The most widely used habitat by shorebirds was mudflats, followed by marshes and plantations. This study revealed that mudflat habitat has high potential in supporting the existence of migratory shorebirds in this area.

How migratory shorebirds selectively exploit prey at a staging site dominated by a single prey species

ABSTRACT Competition intensity depends on the number of competitors and the amount of resources available. Coexistence of potential competitors can be enabled through niche differentiation or high resource availability. Using diet analysis, we investigated which of these 2 mechanisms was in play for coexisting shorebirds at a major staging site in the northern Yellow Sea, China, during northward migration in 2011 and 2012. Competition for food at this site is expected to be intense, with an estimated 250,000 migratory shorebirds gathering annually to refuel over a short period. Great Knots (Calidris tenuirostris), Eurasian Oystercatchers (Haematopus ostralegus osculans), and Red Knots (C. canutus) selected mostly the bivalve Potamocorbula laevis, whereas Bar-tailed Godwits (Limosa lapponica) had a broader diet and showed selection for polychaetes, even though most of their biomass intake was of P. laevis. Although all of these shorebirds fed on P. laevis, they showed different size selection and used diff...

Shorebirds, Stakeholders, and Competing Claims to the Beach and Intertidal Habitat in Delaware Bay, New Jersey, USA

Birds have specific habitat needs as a function of their life cycle and reproductive stage. Migrant shorebirds that may fly from the Arctic to the southern tip of South America have foraging and habitat requirements at sites where they stop to refuel before continuing their migration north or south. Throughout the world, shorebirds mainly forage on mudflats at low tide. Red knots (Calidris canutus rufa) are threatened in the United States and elsewhere, and it is critical to determine factors that might contribute to their decline. This paper uses Delaware Bay as a case study to examine shorebird (and red knot) use of the intertidal habitat, and competing claims to habitats they require during their northward migration, as well as some of the key stakeholders that play a role in protecting red knots. Shorebirds are drawn to Delaware Bay to feed on the eggs of Horseshoe Crabs (Limulus polyphemus) that are concentrated at the high tide. But they also feed on the intertidal mudflat. We examined intertidal habitat use on 17 beaches in an extensive study in 2015, and 5 key beaches in 2016. Most of the beaches were longitudinal, but four were more complex, and were used extensively for resting as well as foraging; numbers there were higher than on the longitudinal beaches. On foraging beaches, some shorebirds were present on over 85% of the intertidal censuses, and red knots were present on over 48% of the intertidal censuses. Average numbers of red knots on the longitudinal beaches varied from 0 to 354 ± 116 when any shorebirds were present, but averaged up to 1184 ± 634 when knots were present in 2015. Some beaches in 2015 had no knots (a beach with long-term aquaculture). Tide, intertidal location, and beach (name) determined the number of knots (and all shorebirds). Numbers decreased with distance from the mean high tide line. The average number of knots present in the intertidal mudflats two hours before or after low tide when knots were present (e.g. no censuses with zeros) was 2040 (=maximum flock size, in 2015). Major threats to red knots are from recreationists, overfishing of horseshoe crabs (reduction in egg prey base), and use of the intertidal by aquaculture. We discuss the role of stakeholders in conservation and protection of red knots.

Extreme migration and the individual quality spectrum

Costs of migration, in terms of time, energy, and mortality risk, have a strong theoretical and empirical foundation in the study of birds. We expect these costs to be most severe for extreme long‐distance migratory landbirds, whose demanding annual routines (e.g. non‐stop flights > 8000 km and return journeys > 30 000 km) may approach their maximum physiological capabilities. To explore whether this is true, we review evidence in long‐jump migratory shorebirds (Scolopacidae), focusing most on the prototypical example, the Alaska‐breeding bar‐tailed godwit Limosa lapponica baueri. Contrary to expectations, these and similar birds demonstrate high adult survival, little evidence for elevated mortality during migration, no apparent minimisation of non‐stop flight distances, and low inter‐ and intra‐individual variation in migration performance. Two key aspects of extreme migrants may explain these findings: 1) a counter‐intuitively conservative annual‐cycle strategy, which minimises risks and enables dissipation of carry‐over effects before fitness consequences arise; and 2) selection pressure during early life, which quickly removes low‐performing individuals from the population. We hypothesise that these two factors, applicable to extreme strategies in a wide range of taxa, act to truncate the range of individual quality in a population, and decrease the prevalence and detectability of carry‐over effects. Testing these hypotheses is challenging, as it requires comparative studies of demography and individual quality spectra along a continuum of extremeness. However, it has important potential implications for interpreting individual variation, designing studies of cross‐seasonal interactions or costs of migration, and recognising early‐warning signs of population decline. For example, the most extreme shorebird migrations rely on abundant but difficult‐to‐access resources; the high minimum individual performance required for survival predicts that degradation of these resource hot‐spots will propel rapid population collapse, rather than incremental declines in condition or performance. Therefore, in extreme migrants, we may paradoxically view populations as operating close to the edge, even while individuals are not.

Tracking the full annual-cycle of the Great Knot, Calidris tenuirostris, a long-distance migratory shorebird of the East Asian-Australasian Flyway

The Great Knot Calidris tenuirostris is one of the iconic long-distance migratory species of the East Asian-Australasian Flyway. However, despite extensive flagging and banding efforts, very little is known about the migratory strategies and the breeding grounds of this species that spends the non-breeding season mainly on the northern shorelines of Australia. Using light-level geolocators deployed on Great Knots at Roebuck Bay (Western Australia), we describe the individual migration strategies, breeding locations and breeding-related behaviour. Based on data from eight successfully tracked individuals, we found that all except one migrated to the western part of the known breeding range. This was 2,000–2,500 km from the eighth individual that commenced breeding in the potentially sep- arated eastern part of the range. Light intensity and temperature profiles provided evidence that four of the birds successfully hatched chicks. Of the three which failed, one appeared to have laid a second clutch before failing again. Arrival at the breeding grounds and the laying of eggs were remarkably synchronous between individuals, as were the arrival dates back at Roebuck Bay. Departure from the breeding grounds was more spread out, partly dependent on breeding success and also as a result of females probably leaving the nesting area before males. The individual migration strategies confirmed the strong dependence of this species on the Yellow Sea as their major stopover site during both southward and northward migration. Furthermore, all individuals stopped at least once on their northward journey to the Yellow Sea from Australia. And in reverse, all individuals stopped at least once on the southward migration before arriving at the Yellow Sea coming from their Arctic breeding grounds. The results indicate that this species will most likely be further affected by the rapid habitat loss in the area of the Yellow Sea and other parts of the Chinese coastline.

Dichotomous strategies? The migration of Whimbrels breeding in the eastern Canadian sub-Arctic

The conservation of migratory birds requires internationally coordinated efforts that, in turn, demand an understanding of population dynamics and connectivity throughout a species' range. Whimbrels (Numenius phaeopus) are a widespread long-distance migratory shorebird with two disparate North American breeding populations. Monitoring efforts suggest that at least one of these populations is declining, but the level of migratory connectivity linking the two populations to specific non-breeding sites or identifiable conservation threats remains unclear. We deployed light-level geolocators in 2012 to track the migration of Whimbrels breeding near Churchill, Manitoba, Canada. In 2013, we recovered 11 of these geolocators, yielding complete migration tracks for nine individuals. During southbound migration, six of the nine Whimbrels stopped at two staging sites on the mid-Atlantic seaboard of the United States for an average of 22 days, whereas three individuals made nonstop flights of ~8000 km from Churchill to South America. All individuals subsequently spent the entire non-breeding season along the northern coasts of Brazil and Suriname. On their way north, all birds stopped at the same two staging sites used during southbound migration. Individuals staged at these sites for an average of 34 days, significantly longer than during southbound migration, and all departed within a 5-day period to undertake nonstop flights ranging from 2600 to 3100 km to the breeding grounds. These extended spring stopovers suggest that female Whimbrels likely employ a mixed breeding strategy, drawing on both endogenous and exogenous reserves to produce their eggs. Our results also demonstrate that this breeding population exhibits a high degree of connectivity among breeding, staging, and wintering sites. As with other long-distance migratory shorebirds, conservation efforts for this population of Whimbrels must therefore focus on a small, but widely spaced, suite of sites that support a large proportion of the population.

Plumage quality mediates a life-history trade-off in a migratory bird

BackgroundMoult is one of the most costly activities in the annual cycle of birds and most avian species separate moult from other energy-demanding activities, such as migration. To this end, young birds tend to undergo the first post-juvenile moult before the onset of migration, but in some species the time window for the pre-migratory feather replacement is too narrow. We hypothesized that in such species an increased investment in the structural quality of juvenile feathers may allow to retain juvenile plumage throughout the entire migratory period and delay moult until arriving at wintering grounds, thus avoiding a moult-migration overlap.MethodsThe effect of juvenile plumage quality on the occurrence of moult-migration overlap was studied in a migratory shorebird, the common snipe Gallinago gallinago. Ca. 400 of first-year common snipe were captured during their final stage of autumn migration through Central Europe. The quality of juvenile feathers was assessed as the mass-length residuals of retained juvenile rectrices. Condition of migrating birds was assessed with the mass of accumulated fat reserves and whole-blood hemoglobin concentration. Path analysis was used to disentangle complex interrelationships between plumage quality, moult and body condition.ResultsSnipe which grew higher-quality feathers in the pre-fledging period were less likely to initiate moult during migration. Individuals moulting during migration had lower fat loads and hemoglobin concentrations compared to non-moulting birds, suggesting a trade-off in resource allocation, where energetic costs of moult reduced both energy reserves available for migration and resources available for maintenance of high oxygen capacity of blood.ConclusionsThe results of this study indicate that a major life-history trade-off in a migratory bird may be mediated by the quality of juvenile plumage. This is consistent with a silver spoon effect, where early-life investment in feather quality affects future performance of birds during migration period. Our results strongly suggest that the juvenile plumage, although retained for a relatively short period of time, may have profound consequences for individuals’ fitness.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0179-4) contains supplementary material, which is available to authorized users.

Challenges faced by shorebird species using the inland wetlands of the East Asian–Australasian Flyway: the little curlew example

Asia is experiencing an alarming rate of inland wetlands loss, posing a risk to the future long-term survival of many species depending on these ecosystems. This review on the status and conservation of the little curlew (Numenius minutus) aims to draw attention to the conservation challenges faced by migratory shorebird species using the inland wetlands of the East Asian–Australasian Flyway (EAAF). Extensive and systematic research survey efforts along the EAAF have focused on species using coastal and tidal areas rather than on species using inland wetlands. Knowledge gaps include functional ecology and physiological responses to quality of food resources, population trends, migratory strategy and the role species play in supporting ecosystems resilience. Studies using remote sensing and geographic information system techniques to track the movements of birds along the flyway and to map habitat condition will prove essential in the future to allow a better understanding of the dynamics occurring at the stopover areas, how birds use resources and what competition pressures exist among species. Ultimately, these studies will contribute to our ability to predict changes and establish management practices for the long-term protection and conservation of the stopover areas for a suite of shorebird species using inland wetlands along the flyway.

Mapping foraging habitat for migratory shorebirds in their Australian non-breeding grounds and prioritising sites for conservation and management

Shorebird populations are declining worldwide as a result of the loss of the intertidal habitats upon which they depend. Conservation status is particularly dire for shorebirds on the East Asian–Australasian Flyway. While the flyway transects many international boundaries and involves numerous bilateral conservation agreements, management of remaining habitat at a local scale is imperative to conserving these species. Coastal habitat is affected by multiple anthropogenic stressors, including loss and degradation due to increasing demand for coastal land. In Australia, migration coincides with the summer holiday season when shorebirds are significantly impacted by human disturbance. Managers are frequently required to make trade-offs between wildlife conservation and anthropogenic land uses and when specific quantitative shorebird habitat data and mapping are absent, human interests will naturally take precedence. This paper demonstrates a method for mapping and prioritising management of shorebird non-breeding habitat using an Australian coastal site, the Richmond River estuary. Foraging habitat was surveyed and mapped using GIS with a range of attributes including habitat types, foraging values, disturbance levels and specific foraging distribution of each species. The results highlighted several important foraging areas that were impacted by disturbance and would require intervening management actions to reduce impacts on shorebirds. The GIS data created provide local managers with an effective tool to consider shorebird habitat in the decision-making process. This method could be replicated at other important shorebird habitat sites, leading to enhanced conservation of these declining species.

Birds of the Patos Lagoon Estuary and adjacent coastal waters, southern Brazil: species assemblages and conservation implications

ABSTRACTEstuarine avifauna is usually diverse, with marked differences along the limnetic to marine gradient and strong influences from physical factors such as salinity, habitat heterogeneity and tidal regime. Here we describe the composition of the avifauna of the Patos Lagoon Estuary and adjacent marine beaches and waters, in southern Brazil, identify the main environmental factors determining variations in species richness along the limnetic-marine gradient, evaluate changes in species composition along this gradient, and discuss the role of the estuary for bird conservation. Overall, 268 bird species were detected at eight sites along the estuary. Despite similar observed richness in spring–summer (247 species) and autumn–winter (244), there was a strong seasonal influence in bird composition due to migrants. Estimated species richness at 94% coverage of sites ranged from 9 to 194.66. Species richness decreased markedly towards the lower estuary, with the single variable ‘distance from the upper estuary’, accounting for the most plausible model. The number of threatened species recorded per site was larger in the lower estuary due the predominance of seabirds and shorebirds on red lists. While the lower estuary holds key feeding and roosting areas for seabirds and shorebirds, the upper estuary harbours more species, mainly forest passerines and waterbirds. Our findings confirm that estuarine gradients strongly influence avian diversity and highlight the importance of estuaries for the conservation of birds, especially migratory sea and shorebirds, and resident saltmarsh-dependent species.

Why fly the extra mile? Latitudinal trend in migratory fuel deposition rate as driver of trans-equatorial long-distance migration.

Trans‐equatorial long‐distance migrations of high‐latitude breeding animals have been attributed to narrow ecological niche widths. We suggest an alternative hypothesis postulating that trans‐equatorial migrations result from a possible increase in the rate at which body stores to fuel migration are deposited with absolute latitude; that is, longer, migrations away from the breeding grounds surpassing the equator may actually enhance fueling rates on the nonbreeding grounds and therewith the chance of a successful, speedy and timely migration back to the breeding grounds. To this end, we first sought to confirm the existence of a latitudinal trend in fuel deposition rate in a global data set of free‐living migratory shorebirds and investigated the potential factors causing this trend. We next tested two predictions on how this trend is expected to impact the migratory itineraries on northward migration under the time‐minimization hypothesis, using 56 tracks of high‐latitude breeding shorebirds migrating along the East Asian‐Australasian Flyway. We found a strong positive effect of latitude on fuel deposition rate, which most likely relates to latitudinal variations in primary productivity and available daily foraging time. We next confirmed the resulting predictions that (1) when flying from a stopover site toward the equator, migrants use long jumps that will take them to an equivalent or higher latitude at the opposite hemisphere; and (2) that from here onward, migrants will use small steps, basically fueling only enough to make it to the next suitable staging site. These findings may explain why migrants migrate “the extra mile” across the equator during the nonbreeding season in search of better fueling conditions, ultimately providing secure and fast return migrations to the breeding grounds in the opposite hemisphere.

Identifying priority sites and gaps for the conservation of migratory waterbirds in China's coastal wetlands

Many waterbird species, in particularly migratory shorebirds, on the East Asian-Australasian Flyway depend on the intertidal areas of coastal China. In recent years, these habitats have suffered severe shrinkage as a result of wetland loss and degradation. Identifying critical areas for waterbirds and assessing conservation status has become an urgent priority for biological conservation. Based on the criteria used to designate Ramsar sites and East Asian-Australasian Flyway Partnership (EAAFP) Flyway Network sites, a general framework is proposed and applied to identify priority sites in China's coastal wetlands using a comprehensive waterbird survey dataset. Sites priority were evaluated by using appearance of globally threatened bird species, and bid species exceeding 1% of their global or flyway population, and population abundance. Sites priorities were ranked using an “irreplaceability index”. Totally, 110 sites are proposed as priority sites. Considering the strategic importance of China's coastal wetlands for migratory waterbirds, the conservation status of China's coastal wetlands is inadequate to protect these waterbirds. Currently, 67 of the 110 priority sites lie outside protected areas. Some critical habitats for waterbirds are not included in individual protected areas, especially in Jiangsu, Zhejiang, and Hebei provinces. Improved protection of these areas is urgently needed. However, conservation efforts in China's coastal wetlands face numerous challenges. Many important intertidal areas are increasingly threatened by ongoing and future reclamation plans. There is an urgent need to re-consider and limit the reclamation, particularly at critical sites, and put in place conservation measures to protect migratory waterbirds and their habitats.

Annual survival rates of migratory shore and upland game birds

ABSTRACTBand recoveries from hunted populations are widely used to estimate survival and harvest rates. We used long‐term (1950–2010) band‐recovery data from the United States and Canada to estimate average survival and recovery rates for juvenile and adult sandhill cranes (Grus canadensis), American coots (Fulica americana), clapper rails (Rallus longirostris), and Wilson's snipe (Gallinago delicata). Banding data were typically sparse and Brownie recovery rates ( f ) were <1% for most species and age classes, so we also utilized encounters from birds banded and recovered throughout the year, including nonhunting recoveries. Estimated juvenile and adult annual survival rates based on combined dead recoveries were 0.917 (SE = 0.080) and 0.884 (SE = 0.006) for sandhill cranes; 0.325 (SE = 0.025) and 0.583 (SE = 0.008) for American coots; 0.368 (SE = 0.070) and 0.500 (SE = 0.025) for clapper rails; and 0.372 (SE = 0.077) and 0.653 (SE = 0.020) for Wilson's snipe. American coots had sufficient band‐recovery data during 1951–1987 to estimate annual process variation in survival for juveniles ( = 0.017) and adults ( = 0.056). Based on average estimated juvenile and adult survival rates for each species, stable populations could be achieved with average annual recruitment rates (expressed as fledged young per adult in the preseason population) of 0.15 (SD = 0.02) for sandhill cranes, 1.26 (SD = 0.19) for American coots, 1.41 (SD = 0.31) for clapper rails, and 0.97 (SD = 0.23) for Wilson's snipe, with uncertainty reflecting measurement error in survival rates. Although band‐recovery models can be successfully applied to small data sets (e.g., 300–3,000 total recoveries in our analyses), juvenile survival estimates lacked precision and annual variation was inestimable for most species, leading to considerable uncertainty for population modeling efforts. © 2016 The Wildlife Society.

Control and consequences of Spartina spp. invasions with focus upon San Francisco Bay

Maritime Spartina spp. are powerful ecosystem engineers that accrete sediment, define shorelines, create habitat, and generate prodigious primary productivity both where they are native and where they have been introduced. Invasive Spartina spp. can compete vigorously with native species, diminish biota, change hydrology, and confound human uses of estuaries. Herbicides have been effective in controlling several Spartina spp. invasions. One of the most recent successes is a 15-year campaign that has virtually eliminated S. alterniflora from the large, century-old invasion in Willapa Bay, WA, USA. Hybridization between native and introduced Spartina spp. has created new species and hybrid swarms. In San Francisco Bay, CA, USA (SF Bay) a complicated situation continues to play out from the purposeful introduction of S. alterniflora, which hybridized with native California cordgrass, S. foliosa. The hybrids spread rapidly and led to a long list of environmental problems, which led to an herbicide program that was successful in greatly diminishing the hybrid and saving the open mud habitat of migratory shorebirds. However, it was belatedly realized that the non-migratory, endangered Ridgeway’s rail uses the tall, dense hybrid Spartina as a surrogate for habitat that was lost during the twentieth century to urbanization and agricultural transformation of marshes around SF Bay. This realization has made difficult the simultaneous management of hybrid Spartina, wildlife conservation, and marsh restoration in San Francisco Bay. Restoration of native vegetation could satisfy the multiple goals of preserving open mud and conserving Ridgeway’s rail.

Why fly the extra mile? Using stress biomarkers to assess wintering habitat quality in migratory shorebirds.

Migratory birds make decisions about how far to travel based on cost-benefit trade-offs. However, in many cases the net effect of these trade-offs is unclear. We sought to address this question by measuring feather corticosterone (CORTf), leucocyte profile, avian malaria parasite prevalence and estimating fueling rates in three spatially segregated wintering populations of the migratory shorebird ruddy turnstone Arenaria interpres during their stay in the winter habitat. These birds fly from the high-Arctic breeding ground to Australia, but differ in that some decide to end their migration early (Broome, Western Australia), whereas others travel further to either South Australia or Tasmania. We hypothesized that the extra costs in birds migrating greater distances and overwintering in colder climates would be offset by benefits when reaching their destination. This would be evidenced by lower stress biomarkers in populations that travel further, owing to the expected benefits of greater resources and improved vitality. We show that avian malaria prevalence and physiological stress levels were lower in birds flying to South Australia and Tasmania than those overwintering in Broome. Furthermore, our modeling predicts that birds in the southernmost locations enjoy higher fueling rates. Our data are consistent with the interpretation that birds occupying more costly wintering locations in terms of higher migratory flight and thermoregulatory costs are compensated by better feeding conditions and lower blood parasite infections, which facilitates timely and speedy migration back to the breeding ground. These data contribute to our understanding of cost-benefit trade-offs in the decision making underlying migratory behaviour.

Diet preferences as the cause of individual differences rather than the consequence.

Behavioural variation within a species is usually explained as the consequence of individual variation in physiology. However, new evidence suggests that the arrow of causality may well be in the reverse direction: behaviours such as diet preferences cause the differences in physiological and morphological traits. Recently, diet preferences were proposed to underlie consistent differences in digestive organ mass and movement patterns (patch residence times) in red knots (Calidris canutus islandica). Red knots are molluscivorous and migrant shorebirds for which the size of the muscular stomach (gizzard) is critical for the food processing rate. In this study, red knots (C.c.canutus, n=46) were caught at Banc d'Arguin, an intertidal flat ecosystem in Mauritania, and released with radio-tags after the measurement of gizzard mass. Using a novel tracking system (time-of-arrival), patch residence times were measured over a period of three weeks. Whether or not gizzard mass determined patch residence times was tested experimentally by offering 12 of the 46 tagged red knots soft diets prior to release; this reduced an individual's gizzard mass by 20-60%. To validate whether the observed range of patch residence times would be expected from individual diet preferences, we simulated patch residence times as a function of diet preferences via a simple departure rule. Consistent with previous empirical studies, patch residence times in the field were positively correlated with gizzard mass. The slope of this correlation, as well as the observed range of patch residence times, was in accordance with the simulated values. The 12 birds with reduced gizzard masses did not decrease patch residence times in response to the reduction in gizzard mass. These findings suggest that diet preferences can indeed cause the observed among-individual variation in gizzard mass and patch residence times. We discuss how early diet experiences can have cascading effects on the individual expression of both behavioural and physiomorphic traits. This emphasizes that to understand the ecological consequences of individual differences, knowledge of the environment during development is required.

Metals from mine waste as potential cause of oxidative stress in burrowing crab Neohelice granulata from San Antonio bay

The Natural Protected Area San Antonio bay is of particular importance for its congregation of migratory shorebirds and it has been declared one of the Western Hemisphere Shorebird Reserve Network International site (WHSRN). Present study represents the first assessment of variation on oxidative stress biomarkers in male crab Neohelice granulata from San Antonio bay (Río Negro, Argentina) under field conditions, associated mainly to metal contamination coming from passive mining wastes. Three sites were sampled once every three months from November 2012 to August 2013 within this sea inlet (Pile, Fishery and Port) and a control site at the southeast of the bay (Punta Perdices). Accumulation of Ni, Zn, Cr and Al varied only with seasons although without a constant trend, meanwhile Cd, Cu and Pb also varied among sites being highest in Pile and Port. Biochemical results indicated that variations in catalase activity was only site specific being maximum in Pile; meanwhile lipid radical, α-tocopherol and metallothioneins were only seasonal specific being higher in autumn and winter. Seasonal variation was also found for total thioles, being the content higher in summer and autumn than in winter. Correlation analysis revealed that malondialdehyde and α-tocopherol have a positive association with Al and negative with Ni, meanwhile GST has a positive association with Fe. Crabs from the closest area to the waste pile did not exhibit a differentiated oxidative pressure despite the higher accumulation of metals. It is possible that crabs from contaminated areas have developed a tolerance to metals, indicating a strong ecotoxicological selective pressure. More studies are needed to assess whether there is a transfer of metals through the food chain.

Continental-scale decreases in shorebird populations in Australia

Decreases in shorebird populations are increasingly evident worldwide, especially in the East Asian—Australasian Flyway (EAAF). To arrest these declines, it is important to understand the scale of both the problem and the solutions. We analysed an expansive Australian citizen-science dataset, spanning the period 1973 to 2014, to explore factors related to differences in trends among shorebird populations in wetlands throughout Australia. Of seven resident Australian shorebird species, the four inland species exhibited continental decreases, whereas the three coastal species did not. Decreases in inland resident shorebirds were related to changes in availability of water at non-tidal wetlands, suggesting that degradation of wetlands in Australia's interior is playing a role in these declines. For migratory shorebirds, the analyses revealed continental decreases in abundance in 12 of 19 species, and decreases in 17 of 19 in the southern half of Australia over the past 15 years. Many trends were strongly associated with continental gradients in latitude or longitude, suggesting some large-scale patterns in the decreases, with steeper declines often evident in southern Australia. After accounting for this effect, local variables did not explain variation in migratory shorebird trends between sites. Our results are consistent with other studies indicating that decreases in migratory shorebird populations in the EAAF are most likely being driven primarily by factors outside Australia. This reinforces the need for urgent overseas conservation actions. However, substantially heterogeneous trends within Australia, combined with declines of inland resident shorebirds indicate effective management of Australian shorebird habitat remains important.

A chain is as strong as its weakest link: assessing the consequences of habitat loss and degradation in a long-distance migratory shorebird

The conservation of migratory species represents a major challenge, as they use multiple sites, all contributing in varying degrees in sustaining high survival and reproductive success. There is particular concern for shorebirds of the East Asian—Australasian Flyway (EAAF), where declining numbers of migratory species have mostly been attributed to habitat loss along the East Asian coast. Using a stochastic dynamic programming migration model, we assessed the effect of habitat degradation scenarios along the EAAF on migration behaviour, survival and reproductive success of a long-distance migrating shorebird, the Ruddy Turnstone (Arenaria interpres). Following manipulation of habitat quality through changes in intake rate, we found that changes on the wintering (major non-breeding) ground in South Australia had the highest negative effect on reproductive success and survival. We also identified Taiwan and the Yellow Sea as sites with high importance for reproductive success. Although habitats along the East Asian coastline are currently most threatened from a range of global change processes, we highlight the importance of conserving high-quality shorebird wintering habitat in Australia. This may be of notable importance to trans-equatorial migratory shorebirds, which often make a long non-stop flight from their wintering grounds in order to skip low-latitude sites that typically provide little food.

Reclamation of tidal flats and shorebird declines in Saemangeum and elsewhere in the Republic of Korea

Saemangeum, in the Republic of Korea (ROK, commonly called South Korea) was one of the most important shorebird staging sites in the Yellow Sea. It supported at least 330 000 shorebirds annually between 1997 and 2001, including ∼30% of the world population of Great Knots (Calidris tenuirostris) during both northward and southward migration. Construction of a 33-km long sea-wall was completed in April 2006. We show that shorebird numbers at Saemangeum and two adjacent wetlands decreased by 130 000 during northward migration in the next two years and that all species have declined at Saemangeum since completion of the sea-wall. Great Knots were among the most rapidly affected species. Fewer than 5000 shorebirds were recorded at Saemangeum during northward migration in 2014. We found no evidence to suggest that most shorebirds of any species displaced from Saemangeum successfully relocated to other sites in the ROK. Instead, by 2011–13 nearly all species had declined substantially in the ROK since previous national surveys in 1998 and 2008, especially at more heavily reclaimed sites. It is likely that these declines were driven by increased mortality rather than movement to alternate staging sites given that other studies have shown concurrent declines in numbers and survival on the non-breeding grounds. This is the first study in the East Asian—Australasian Flyway to confirm declines of shorebirds at a range of geographical scales following a single reclamation project. The results indicate that if migratory shorebirds are displaced from major staging sites by reclamation they are probably unable to relocate successfully to alternate sites.