Understanding declines in the population size of migratory birds

The common sandpiper is an Afro-Palearctic migrant that is declining across Europe. Studies have suggested that environmental conditions during winter are likely to be important determinants of their population trends, but these trends differ between breeding regions suggesting that wintering conditions are not the only important factor. We investigated the factors affecting common sandpipers during each of their lifecycle stages to obtain a complete overview of the factors affecting their status. During the breeding season, we found that disturbance appears to have an important effect on the probability of a nest hatching successfully. Further, we found that heavy rainfall in the week after hatching reduced the probability of chicks fledging, presumably through the influence of poor weather on thermoregulation and foraging. Common sandpipers are known to be associated with areas of high water quality. In winter, common sandpipers were more likely to be found in areas of low salinity and high pH, and had higher foraging success in these areas, suggesting that water chemistry might be an important influence on their habitat selection. Further, we showed that common sandpipers are territorial in winter, which has previously only been suggested based on anecdotal evidence. Studies of many other species have shown that the conditions during migration are likely to be a key driver of population trends. We investigated the migration of individuals across multiple populations using geolocators, tagging common sandpipers in England and Senegal, and combining these data with published data from individuals tagged in Scotland. We revealed that there is a large amount of overlap in the non-breeding distributions of individuals from these populations. Also, we showed that birds appear to use wind to facilitate their migration in autumn, but actively fly against prevailing conditions in spring. Finally, we investigated changes in the timing of wading bird migration at a flyway scale using the eBird citizen science dataset. We showed that, contrary to the findings of many studies, the timing of migration seems to be becoming later at a flyway scale and suggest range shifts as the primary driver. Understanding the influence of conditions at each lifecycle stage is paramount for determining the drivers of declining migratory bird populations. Further, investigating the mechanisms driving population trends in individual species will help us to understand the patterns we see at larger spatial scales

Dispersions of ellipsoidal particles in a nematic liquid crystal

Colloidal particles dispersed in a partially ordered medium, such as a liquid crystal (LC) phase, disturb its alignment and are subject to elastic forces. These forces are long-ranged, anisotropic and tunable through temperature or external fields, making them a valuable asset to control colloidal assembly. The latter is very sensitive to the particle geometry since it alters the interactions between the colloids. We here present a detailed numerical analysis of the energetics of elongated objects, namely prolate ellipsoids, immersed in a nematic host. The results, complemented with qualitative experiments, reveal novel LC configurations with peculiar topological properties around the ellipsoids, depending on their aspect ratio and the boundary conditions imposed on the nematic order parameter. The latter also determine the preferred orientation of ellipsoids in the nematic field, because of elastic torques, as well as the morphology of particles aggregates.Comment: 31 pages, 11 figure

From compressibility to structural investigation of sodium dodecyl sulphate — Part 1: Powder and tablet physico-chemical characteristics

As a part of a study on detergent tablets, investigations were carried out to elucidate the compression behavior of a powdered surfactant, sodium dodecyl sulphate (SDS), based on a comparison with the main component of the formulation, i.e. the chorine provider (DCCNa). The compacted SDS exhibited poor cohesion as well as delayed dissolution whatever the compression pressure. The microscopic observations and the mercury porosimetry measurements both demonstrated that a residual porosity existed in the tablets but the dissolution times were always long. A modification of SDS in contact with water, forming a structure like a gel, probably occurred, inducing the closing of the pores and thereby limiting the water intrusion into the tablets

The effects of geolocators on return rates, condition, and breeding success in Common Sandpipers Actitis hypoleucos

Capsule : Fitting geolocators to Common Sandpipers Actitis hypoleucos did not affect their return rates, return dates, body condition or reproductive success, but did cause leg injuries in some individuals. Aims : To investigate the effect of fitting geolocators to Common Sandpipers on their return rates and timing, the condition in which they return and their subsequent breeding success. Methods : We fitted geolocators to colour-ringed Common Sandpipers and monitored them throughout the breeding seasons prior to migration and following return from their wintering grounds. We then compared return rate, return date, change in body condition, hatching success, and fledging success between birds with and without the tags. We also fitted a number of smaller geolocators to wintering individuals in Africa and compared their return rates with a control group. Results : We found no significant differences between birds with and without geolocators in any of the variables measured. However, several individuals fitted with the larger tags were found to have incurred leg injuries. Conclusion : Our study highlights the need for complete transparency when reporting the effects of geolocators and shows the importance of continuous monitoring of individuals when carrying out tracking studies

Climatic conditions during migration affect population size and arrival dates in an Afro-Palaearctic migrant:Climate and demography in sand martins

Long-distance migrants are particularly susceptible to climate change because of their multi-stage life-cycle, but understanding how climatic conditions at each of these stages influence population dynamics remains a key challenge. Here, we use long-term data from a UK population of Sand Martins Riparia riparia, a declining Afro-Palaearctic migrant, to investigate how weather on the wintering grounds and at passage sites impacts population size and arrival date. General linear models revealed that population size increased and arrival date advanced over the study period, and both were predicted by regional climatic variables in the previous winter and on passage. These results add to a growing body of evidence showing that population change in migrant birds is influenced by climatic conditions at all stages of the life cycle

Willis metamaterial on a structured beam

Bianisotropy is common in electromagnetics whenever a cross-coupling between electric and magnetic responses exists. However, the analogous concept for elastic waves in solids, termed as Willis coupling, is more challenging to observe. It requires coupling between stress and velocity or momentum and strain fields, which is difficult to induce in non-negligible levels, even when using metamaterial structures. Here, we report the experimental realization of a Willis metamaterial for flexural waves. Based on a cantilever bending resonance, we demonstrate asymmetric reflection amplitudes and phases due to Willis coupling. We also show that, by introducing loss in the metamaterial, the asymmetric amplitudes can be controlled and can be used to approach an exceptional point of the non-Hermitian system, at which unidirectional zero reflection occurs. The present work extends conventional propagation theory in plates and beams to include Willis coupling, and provides new avenues to tailor flexural waves using artificial structures.Comment: 21 pages, 3 figure

From compressibility to structural investigation of sodium dodecyl sulphate — Part 2: A singular behavior under pressure

Investigations were carried out to elucidate the compression behavior of a powdered surfactant, sodium dodecyl sulphate (SDS), based on a comparison with the main component of a detergent formulation, i.e. the chorine provider (DCCNa). The energetic analysis based on the compression cycles highlighted a lower compressibility of SDS compared with DCCNa, especially due to its worse packing ability, larger elasticity and bad cohesion ability. Also, it pointed out that the pycnometric density seemed to be overrun under pressure whereas a residual porosity had been evidenced in the expanded tablets. DSC/DTA analysis, Raman spectroscopy as well as powder X-ray diffraction refuted the hypothesis of a physico-chemical transformation of SDS under pressure. This was in accordance with the morphology of the SDS particles, quite unchanged after compression. The pycnometric density measurements have been improved; firstly, it allowed to properly express the compaction ratio of the ejected SDS tablets, and secondly, it led to conclude to a reversible intrinsic compressibility for pressures higher than 50 MPa, explained by the predominant elastic behavior of SDS

Adaptive sampling by citizen scientists improves species distribution model performance: a simulation study

1. Volunteer recorders generate large amounts of biodiversity data through citizen science which is used in conservation planning and policy decision-making. Unstructured sampling, where the volunteer can record what they want, where they want, leads to spatial unevenness in these data. While there are many statistical techniques to account for the resulting biases, it may be possible to improve datasets by directing a subset of recorders to sample in the most informative locations, known as adaptive sampling. We investigated the potential for adaptive sampling to improve the performance of species distribution models built on citizen science data using simulated ecological communities. 2. We simulated ecological assemblages across Great Britain based on current butterfly data and modelled the distributions of each species. We then simulated the sampling of new data based on five adaptive sampling methods (one empirical method based simply on gap-filling, and four model-based methods using various measures from the model outputs) and one non-adaptive method (a method in which recording continued in the current pattern), and re-ran the species distribution models. In these, we also varied the rate of recording effort that was distributed according to adaptive sampling. The model predictions using the original and adaptively sampled data were compared to true species distributions to evaluate the performance of each method. 3. We found that all adaptive sampling approaches improved model performance, with greatest improvement for model-based approaches compared to the empirical sampling method (i.e. simple gap-filling). All four model-based adaptive sampling approaches provided similar benefits for model outputs. Improvements in model performance were greatest when the amount of adaptive sampling changed from no uptake to 1% uptake, indicating that only a small amount of change in recorder behaviour is needed to improve model performance. 4. Directing volunteer recorders to places where records are most needed, based on information from model outputs, can improve species distribution models built on citizen science data, even with minimal uptake of suggested locations. Our results therefore suggest that adaptive sampling by recorders could be beneficial for real-world citizen science datasets

Pressure effects on the resonant attenuation of soft porous beads-based materials for underwater acoustics

Dedicated coating materials for anechoism and furtivity in underwater acoustics must exhibit a strong reliability regarding their mechanical resistance to hydrostatic pressure. Soft porous materials, especially, a distribution of soft porous beads within a polyurethane matrix, have been previously proposed as an acoustic insulator device. The purpose of the present letter is to investigate the attenuation efficiency of soft porous silicone beads-based materials while being exposed to uniaxial loads mimicking hydrostatic pressures encountered in underwater acoustics. The acoustic performance of this locally resonant material is then compared to the classical coating technology using micro-balloons. The use of an adapted surfactant (a silicone alkyl polyether compound) in the fabrication process of the soft porous silicone-based beads, obtained through an emulsion templating process, leads to particles exhibiting an open porosity. The (resonant) attenuation of the soft porous beads-based material remains greater than the micro-balloons-based material until several bars. Above this critical resilience value, the mechanical stress irreversibly damages the soft porous beads