Low migratory connectivity and similar migratory strategies in a shorebird with contrasting wintering population trends in Europe and West Africa.

Migratory shorebird populations are declining worldwide, showing an apparent inability to respond to the interplaying challenges emerging along their flyways. Within the East Atlantic Flyway, non-breeding populations show moderate to strong declines in Sub-Saharan Africa, contrasting with stable or increasing trends in Europe. Local factors are insufficient to explain the opposite tendencies and, therefore, investigating migratory strategies and connectivity of these populations may help identifying the drivers of their demography. We followed the migratory journeys of 20 grey plovers (Pluvialis squatarola) from their wintering grounds in Guinea-Bissau (West Africa), Portugal and France (Europe) using tracking devices. Grey plovers wintering in Africa and Europe were found to share breeding grounds at European Russia and Western Siberia, revealing low migratory connectivity in the Eastern Atlantic population. All individuals followed a "skipping" migratory strategy, flying mostly mid-distance bouts, and using an unexpected large network of stopover sites to re-fuel usually for short periods. We identified 66 different stopover sites along the West African, European and Russian/Siberian coasts. All birds stopped at the Wadden Sea in both migratory periods, highlighting the importance of this region and the risk for a potential bottleneck. Low migratory connectivity and similar migratory strategies shared by grey plovers wintering in Europe and West Africa do not support their contrasting population trends.

Isotopic niches of the Northern shoveler Spatula clypeata in spring migratory stopover sites in the Marais breton, France.

The Northern shoveler, Spatula clypeata, makes several migratory stopovers to reach its breeding site in the best conditions. These stopovers allow the species to replenish their reserves. Therefore, feeding efficiency at such sites is essential. Despite its importance, few studies have been conducted on the spring ecology of the shoveler, particularly on its diet at stopover sites. Therefore, this study focused on the Northern shoveler's feeding habit during its spring migratory stopover in the Marais breton (MB), a wetland situated in Vendée (France, Atlantic coast). The shoveler's plasma and potential food resources were studied using a stable carbon and nitrogen isotope analysis. The study showed that the shoveler feeds primarily on microcrustaceans, especially Cladocera and Copepoda; Chironomidae larvae, Corixidae, Hydrophilidae larvae, and particulate organic matter. This last food source, the POM, had never been highlighted before.

Behavioral responses to offshore windfarms during migration of a declining shorebird species revealed by GPS-telemetry.

EU member countries and the UK are currently installing numerous offshore windfarms (OWFs) in the Baltic and North Seas to achieve decarbonization of their energy systems. OWFs may have adverse effects on birds; however, estimates of collision risks and barrier effects for migratory species are notably lacking, but are essential to inform marine spatial planning. We therefore compiled an international dataset consisting of 259 migration tracks for 143 Global Positioning System-tagged Eurasian curlews (Numenius arquata arquata) from seven European countries recorded over 6 years, to assess individual response behaviors when approaching OWFs in the North and Baltic Seas at two different spatial scales (i.e. up to 3.5 km and up to 30 km distance). Generalized additive mixed models revealed a significant small-scale increase in flight altitudes, which was strongest at 0-500 m from the OWF and which was more pronounced during autumn than during spring, due to higher proportions of time spent migrating at rotor level. Furthermore, four different small-scale integrated step selection models consistently detected horizontal avoidance responses in about 70% of approaching curlews, which was strongest at approximately 450 m from the OWFs. No distinct, large-scale avoidance effects were observed on the horizontal plane, although they could possibly have been confounded by changes in flight altitudes close to land. Overall, 28.8% of the flight tracks crossed OWFs at least once during migration. Flight altitudes within the OWFs overlapped with the rotor level to a high degree in autumn (50%) but to a significantly lesser extent in spring (18.5%). Approximately 15.8% and 5.8% of the entire curlew population were estimated to be at increased risk during autumn and spring migration, respectively. Our data clearly show strong small-scale avoidance responses, which are likely to reduce collision risk, but simultaneously highlight the substantial barrier effect of OWFs for migrating species. Although alterations in flight paths of curlews due to OWFs seem to be moderate with respect to the overall migration route, there is an urgent need to quantify the respective energetic costs, given the massive ongoing construction of OWFs in both sea areas.

Morphological, calorific and nutritive characteristics of 656 freshwater invertebrates taxa.

BACKGROUND: The Freshwater Animal Diversity Assessment (FADA) project estimated that freshwater animal species represent 9.5% of the 1.2 million species described. Knowing that freshwater represents only 0.01% of the earth's surface, these wetlands are suitable habitats for a great part of the world's total biodiversity. However, it has been shown that there is a lack of knowledge on these species, including freshwater invertebrates. Nevertheless, they play a key role in the majority of freshwater ecosystems and in their foodweb networks. Freshwater invertebrates are the food resource of many species, such as fish and birds. The knowledge of their morphological, energetic and nutritive characteristics allows a better understanding of their selection by predators (size, energy intake etc.), but also leads to the improvement of wetland management. Although information about freshwater invertebrates exists in literature, they are generally heterogeneous, dispersed and difficult to collect. To facilitate the accessibility of these data and, thus, optimise and accelerate research projects including freshwater invertebrates, we propose a literature review describing 14 morphological and nutritive characteristics (size, dry weight, gross energy, crude protein etc.) for 656 taxa of freshwater invertebrates. NEW INFORMATION: This dataset is a review from 104 publications from 1935 to 2020, compiling 14 characteristics when available (size, dry weight, gross energy, crude protein etc.) for 656 taxa of freshwater invertebrates.

Timing of spring departure of long distance migrants correlates with previous year's conditions at their breeding site.

Precise timing of migration is crucial for animals targeting seasonal resources at locations encountered across their annual cycle. Upon departure, long-distance migrants need to anticipate unknown environmental conditions at their arrival site, and they do so with their internal annual clock. Here, we tested the hypothesis that long-distance migrants synchronize their circannual clock according to the phenology of their environment during the breeding season and therefore adjust their spring departure date according to the conditions encountered at their breeding site the year before. To this end, we used tracking data of Eurasian curlews from different locations and combined movement data with satellite-extracted green-up dates at their breeding site. The spring departure date was better explained by green-up date of the previous year, while arrival date at the breeding site was better explained by latitude and longitude of the breeding site, suggesting that other factors impacted migration timing en route. On a broader temporal scale, our results suggest that long-distance migrants may be able to adjust their migration timing to advancing spring dates in the context of climate change.

Migrating curlews on schedule: departure and arrival patterns of a long-distance migrant depend on time and breeding location rather than on wind conditions.

BACKGROUND: Departure decisions in long-distance migratory bird species may depend on favourable weather conditions and beneficial resources at the destination location, overarched by genetic triggers. However, few studies have tried to validate the significance of these three concepts simultaneously, and long-term, high-resolution tagging datasets recording individual movements across consecutive years are scarce. We used such a dataset to explore intraspecific and intra-individual variabilities in departure and arrival decisions from/to wintering grounds in relation to these three different concepts in bird migration. METHODS: We equipped 23 curlews (Numenius arquata) wintering in the Wadden Sea with Global Positioning System data loggers to record their spatio-temporal patterns of departure from and arrival at their wintering site, and the first part of their spring migration. We obtained data for 42 migrations over 6 years, with 12 individuals performing repeat migrations in consecutive years. Day of year of departure and arrival was related to 38 meteorological and bird-related predictors using the least absolute shrinkage and selection operator (LASSO) to identify drivers of departure and arrival decisions. RESULTS: Curlews migrated almost exclusively to Arctic and sub-Arctic Russia for breeding. They left their wintering site mainly during the evening from mid- to late April and returned between the end of June and mid-July. There was no difference in departure times between the sexes. Weather parameters did not impact departure decisions; if departure days coincided with headwind conditions, the birds accounted for this by flying at higher altitudes of up to several kilometres. Curlews breeding further away in areas with late snowmelt departed later. Departures dates varied by only < 4 days in individual curlews tagged over consecutive years. CONCLUSIONS: These results suggest that the trigger for migration in this long-distance migrant is largely independent of weather conditions but is subject to resource availability in breeding areas. The high intra-individual repeatability of departure days among subsequent years and the lack of relationship to weather parameters suggest the importance of genetic triggers in prompting the start of migration. Further insights into the timing of migration in immatures and closely related birds might help to further unravel the genetic mechanisms triggering migration patterns.

Tracing changes in the diet and habitat use of black-tailed godwits in Western France, using a stable isotope approach.

Western France is at the crossroads of the migratory routes of two subspecies of black-tailed godwit, Limosa limosa. After leaving Iceland, the godwit L.l. islandica Icelandic black-tailed godwit (IBTG) winters on the coast of western Europe, while the continental black-tailed godwit (CBTG) L.l. limosa can stop in France when migrating between Iberia or Africa and their main breeding grounds in the Netherlands. In this study, we analysed δ15N and δ13C from flight feathers and whole blood throughout the non-breeding period to trace variations in habitat use for both subspecies on the western French coast. Adults and juveniles of IBTG adopt the same feeding habitats as soon as they arrive in the study area, progressively losing the Icelandic freshwater habitat signal, and becoming clearly restricted to marine habitats in winter. Some individuals begin to move locally to freshwater habitats, joining CBTG in a stopover at the end of the wintering period in preparation for northward migration.

Building a database for long-term monitoring of benthic macrofauna in the Pertuis-Charentais (2004-2014).

BACKGROUND: Long-term benthic monitoring is rewarding in terms of science, but labour-intensive, whether in the field, the laboratory, or behind the computer. Building and managing databases require multiple skills, including consistency over time as well as organisation via a systematic approach. Here, we introduce and share our spatially explicit benthic database, comprising 11 years of benthic data. It is the result of intensive benthic sampling that has been conducted on a regular grid (259 stations) covering the intertidal mudflats of the Pertuis-Charentais (Marennes-Oléron Bay and Aiguillon Bay). Samples were taken by foot or by boats during winter depending on tidal height, from December 2003 to February 2014. The present dataset includes abundances and biomass densities of all mollusc species of the study regions and principal polychaetes as well as their length, accessibility to shorebirds, energy content and shell mass when appropriate and available. This database has supported many studies dealing with the spatial distribution of benthic invertebrates and temporal variations in food resources for shorebird species as well as latitudinal comparisons with other databases. In this paper, we introduce our benthos monitoring, share our data, and present a "guide of good practices" for building, cleaning and using it efficiently, providing examples of results with associated R code. NEW INFORMATION: The dataset has been formatted into a geo-referenced relational database, using PostgreSQL open-source DBMS. We provide density information, measurements, energy content and accessibility of thirteen bivalve, nine gastropod and two polychaete taxa (a total of 66,620 individuals)​ for 11 consecutive winters. Figures and maps are provided to describe how the dataset was built, cleaned, and how it can be used. This dataset can again support studies concerning spatial and temporal variations in species abundance, interspecific interactions as well as evaluations of the availability of food resources for small- and medium size shorebirds and, potentially, conservation and impact assessment studies.

Key features of intertidal food webs that support migratory shorebirds.

The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain--Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds.

Evidence of species-specific detoxification processes for trace elements in shorebirds.

This study investigated sub-lethal effects and detoxification processes activated in free-ranging Red Knots (RKs) (Calidris canutus) from the Pertuis Charentais on the Atlantic coast of France, and compared the results with previous data obtained on another shorebird species, the Black-tailed Godwit (Limosa limosa). The concentrations of 13 trace elements (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Zn) were assessed in the liver, kidneys, muscle and feathers. Stable isotope analyses of carbon and nitrogen were carried out to determine whether differences in diet explained variations in elemental uptake. The mRNA expression of relevant genes (cytochrome c oxidase 1, acetyl-CoA carboxylase, Cu/Zn and Mn superoxide dismutase, catalase, metallothionein, malic enzyme), antioxidant enzyme activities (catalase, glutathione peroxidase (GPx), superoxide dismutase), and metallothionein (MT) levels were investigated to shed light on trace element detoxification and toxic effects. Although Red Knots were characterized by elevated As and Se concentrations which were potentially toxic, most elements were usually below toxicity threshold levels. The results strongly suggested a dietary specialization of Red Knots, with individuals feeding on higher trophic status prey experiencing higher As, Hg and Se burdens. Red Knots and Godwits also showed discrepancies in elemental accumulation and detoxification processes. Higher As and Se concentrations in Red Knots enhanced catalase gene expression and enzyme activity, while Godwits had higher Ag, Cu, Fe and Zn levels and showed higher MT production and GPx activity. The results strongly suggest that detoxification pathways are essentially trace element- and species-specific.

Insight on trace element detoxification in the Black-tailed Godwit (Limosa limosa) through genetic, enzymatic and metallothionein analyses.

Trace element concentrations (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Zn) were investigated in the liver, kidneys, muscle and feathers of 31 black-tailed godwits (Limosa limosa) accidentally killed during catches by mist net in the Pertuis Charentais, Atlantic coast of France. Analyses of carbon and nitrogen stable isotope ratios were carried out in liver, muscle and feathers in order to elucidate dietary patterns and to determine whether differences in diet explained the variation in elemental uptake. This study also aimed to have a preliminary assessment of sub-lethal effects triggered by trace elements through the investigation of gene expressions by quantitative real-time PCR, antioxidant enzyme activities (catalase, superoxide dismutase, glutathione peroxidase), and metallothionein (MT) levels. The results showed that Cr and Ni concentrations in tissues of adults were lower than in juveniles in part because adults may have eliminated these trace elements through moulting. Except for Cd and Ni, trace element concentrations were negatively correlated to the body mass of godwits. Ag, As, Hg and Se concentrations were positively linked with the trophic position of birds. The diet could be considered as a fundamental route of exposure for these elements demonstrating therefore the qualitative linkage between dietary habits of godwits and their contaminant concentrations. Our results strongly suggest that even though trace element concentrations were mostly below toxicity threshold level, the elevated concentrations of As, Ag, Cd, Cu, Fe and Se may however trigger sub-lethal effects. Trace elements appear to enhance expression of genes involved in oxidative stress defence, which indicates the production of reactive oxygen species. Moreover, birds with the highest concentrations appeared to have an increased mitochondrial metabolism suggesting that the fight against trace element toxicity requires additional energetic needs notably to produce detoxification mechanisms such as metallothioneins.

Scaling up ideals to freedom: are densities of red knots across western Europe consistent with ideal free distribution?

Local studies have shown that the distribution of red knots Calidris canutus across intertidal mudflats is consistent with the predictions of an ideal distribution, but not a free distribution. Here, we scale up the study of feeding distributions to their entire wintering area in western Europe. Densities of red knots were compared among seven wintering sites in The Netherlands, UK and France, where the available mollusc food stocks were also measured and from where diets were known. We tested between three different distribution models that respectively assumed (i) a uniform distribution of red knots over all areas, (ii) a uniform distribution across all suitable habitat (based on threshold densities of harvestable mollusc prey), and (iii) an ideal and free distribution (IFD) across all suitable habitats. Red knots were not homogeneously distributed across the different European wintering areas, also not when considering suitable habitats only. Their distribution was best explained by the IFD model, suggesting that the birds are exposed to interference and have good knowledge about their resource landscape at the spatial scale of NW Europe, and that the costs of movement between estuaries, at least when averaged over a whole winter, are negligible.

Stochastic atmospheric assistance and the use of emergency staging sites by migrants.

Numerous animals move vast distances through media with stochastic dynamic properties. Avian migrants must cope with variable wind speeds and directions en route, which potentially jeopardize fine-tuned migration routes and itineraries. We show how unpredictable winds affect flight times and the use of an intermediate staging site by red knots (Calidris canutus canutus) migrating from west Africa to the central north Siberian breeding areas via the German Wadden Sea. A dynamic migration model incorporating wind conditions during flight shows that flight durations between Mauritania and the Wadden Sea vary between 2 and 8 days. The number of birds counted at the only known intermediate staging site on the French Atlantic coast was strongly positively correlated with simulated flight times. In addition, particularly light-weight birds occurred at this location. These independent results support the idea that stochastic wind conditions are the main driver of the use of this intermediate stopover site as an emergency staging area. Because of the ubiquity of stochastically varying media, we expect such emergency habitats to exist in many other migratory systems, both airborne and oceanic. Our model provides a tool to quantify the effect of winds and currents en route.

Diet selection in a molluscivore shorebird across Western Europe: does it show short- or long-term intake rate-maximization?

1. Studies of diet choice usually assume maximization of energy intake. The well-known 'contingency model' (CM) additionally assumes that foraging animals only spend time searching or handling prey. Despite considerable empirical support, there are many foraging contexts in which the CM fails, but such cases were considered exceptions rather than the rule. 2. For animals constrained by the rate at which food is digested, CM does not necessarily lead to maximal energy intake rates because the time for digestion is not part of the selection criteria. In the main model developed to explain diet choice under a digestive constraint, the 'digestive rate model' (DRM), time lost to digestive breaks is minimized so that energy intake over total time (searching, handling, digestive breaks) is maximized. 3. It is increasingly acknowledged that most animals may face digestive constraints as prey capture rates vary over time and as it would be a waste to carry around heavy digestive machinery that can rapidly process food under all circumstances: this is only needed in times of high demand, provided that enough food can be found. 4. In molluscivore shorebirds ingesting hard-shelled prey such as red knots (Calidris canutus), the predictions of DRM were held up so far, whereas those of CM were rejected. However, most tests were carried out under controlled experimental conditions. Red knots overwinter in coastal areas over much of Western Europe and we capitalized on this variation by comparing, during a single winter, observed diet composition with predictions of DRM, CM and a null model assuming no prey selection ('no-selection model', NSM). 5. The observed diets were best predicted by DRM followed by CM. NSM poorly predicted observed diet choice. Under the present conditions, diet choice based on DRM would on average have yielded an energy intake rate twice as large as one based on CM. By adjusting the size of their gizzard (held constant in the present simulations), red knots could have lifted their energy intake rate further. We suggest that application of the DRM can help many diet studies forward, especially those previously seen as exceptions to the classical CM-based rule.