Reintroduction ecology of the Eurasian crane Grus grus

Successful conservation strategies to increase the survival prospects of a population must be accompanied by an accurate knowledge of the population dynamics. In this thesis, I examine the population dynamics of Eurasian cranes (Grus grus) in the UK and assess the impact of a reintroduction on the future population size and distribution. Additionally, I cover other aspects of crane conservation, such as public engagement in crane conservation and crane resilience to extreme weather events. To do so, I use a wide range of tools: Internet-based monitoring methods, stochastic matrix population models, point process models and GPS-accelerometer tracking devices. I show that there is a geographic gradient in interest in reintroduction projects; people living near the project area have a greater interest than people from areas further away. I also show that the UK crane population is acting as a pseudo-sink; current levels of survival and productivity allow the population’s persistence but immigration is driving population recovery. Nevertheless, the productivity of the UK population is low and measures to improve it should be implemented. The reintroduction of 90 birds in the Somerset Levels has decreased the relative importance of immigration and is likely to increase the projected population size by 50% over the next 50 years. However, the increase in population numbers will not be accompanied by a large expansion in the population range. Cranes will likely colonize large wetlands with low perimeter-to-area ratios near already occupied areas, but the reintroduction will increase the dispersal potential of the species. Finally, I find that during an extreme flooding event, crane foraging areas became limited to a small unflooded patch, but cranes coped with this event through behavioural flexibility, by increasing their foraging time. Together, these results highlight the importance of reaching a broad understanding of population dynamics in order to implement effective conservation strategies

Timing is critical : consequences of asynchronous migration for the performance and destination of a long-distance migrant

Background Migration phenology is shifting for many long-distance migrants due to global climate change, however the timing and duration of migration may influence the environmental conditions individuals encounter, with potential fitness consequences. Species with asynchronous migrations, i.e., with variability in migration timing, provide an excellent opportunity to investigate how of the conditions individuals experience during migration can vary and affect the migratory performance, route, and destination of migrants. Methods Here, we use GPS tracking and accelerometer data to examine if timing of autumn migration influences the migratory performance (duration, distance, route straightness, energy expenditure) and migration destinations of a long-distance, asynchronous, migrant, the white stork (Ciconia ciconia). We also compare the weather conditions (wind speed, wind direction, and boundary layer height) encountered on migration and examine the influence of wind direction on storks' flight directions. Results From 2016 to 2020, we tracked 172 white storks and obtained 75 complete migrations from the breeding grounds in Europe to the sub-Saharan wintering areas. Autumn migration season spanned over a 3-month period (July-October) and arrival destinations covered a broad area of the Sahel, 2450 km apart, from Senegal to Niger. We found that timing of migration influenced both the performance and conditions individuals experienced: later storks spent fewer days on migration, adopted shorter and more direct routes in the Sahara Desert and consumed more energy when flying, as they were exposed to less supportive weather conditions. In the Desert, storks' flight directions were significantly influenced by wind direction, with later individuals facing stronger easterly winds (i.e., winds blowing to the west), hence being more likely to end their migration in western areas of the Sahel region. Contrastingly, early storks encountered more supportive weather conditions, spent less energy on migration and were exposed to westerly winds, thus being more likely to end migration in eastern Sahel. Conclusions Our results show that the timing of migration influences the environmental conditions individuals face, the energetic costs of migration, and the wintering destinations, where birds may be exposed to different environmental conditions and distinct threats. These findings highlight that on-going changes in migration phenology, due to environmental change, may have critical fitness consequences for long-distance soaring migrants.Peer reviewe

Urohidrosis as an overlooked cooling mechanism in long-legged birds

Behavioural thermoregulation could buffer the impacts of climate warming on vertebrates. Specifically, the wetting of body surfaces and the resulting evaporation of body fluids serves as a cooling mechanism in a number of vertebrates coping with heat. Storks (Ciconiidae) frequently excrete onto their legs to prevent overheating, a phenomenon known as urohidrosis. Despite the increasingly recognised role of bare and highly vascularised body parts in heat exchange, the ecological and evolutionary determinants of urohidrosis have been largely ignored. We combine urohidrosis data from a scientifically curated media repository with microclimate and ecological data to investigate the determinants of urohidrosis in all extant stork species. Our phylogenetic generalised linear mixed models show that high temperature, humidity and solar radiation, and low wind speed, promote the use of urohidrosis across species. Moreover, species that typically forage in open landscapes exhibit a more pronounced use of urohidrosis than those mainly foraging in waterbodies. Substantial interspecific variation in temperature thresholds for urohidrosis prevalence points to different species vulnerabilities to high temperatures. This integrated approach that uses online data sources and methods to model microclimates should provide insight into animal thermoregulation and improve our capacity to make accurate predictions of climate change’s impact on biodiversityinfo:eu-repo/semantics/publishedVersio

Age mediates access to landfill food resources and foraging proficiency in a long-lived bird species

Human activities have altered the availability of resources for wildlife. Landfill sites now provide abundant and predictable anthropogenic food subsidies worldwide, sustaining increasing numbers of opportunistic species and shaping their foraging behaviour. However, although individuals may differ in their ability to use these resources, the factors influencing this variability within species are still poorly known. Using GPS data from 68 adult and 67 juvenile white storks, Ciconia ciconia, tracked during their premigratory periods between 2018 and 2020, we investigated whether age determines landfill attendance and the ability to compete for space and food. Additionally, using video recordings of 165 adults and 124 juveniles obtained in the 2020 premigratory period, we investigated whether age influences landfill foraging proficiency and dominance over resources. Adult storks visited landfills on 57% of the days, while juveniles only visited landfills on 29% of the days. There was strong competition for food at landfills, with adults exerting dominance over juveniles, foraging predominantly in areas with higher food availability and outcompeting juveniles in food acquisition. Juveniles had significantly lower food intake rates in the best foraging areas and showed less aggressiveness, being forced to use adjacent lower quality areas. Overall, juveniles had limited access to landfill resources, suggesting that landfill diet specialization is mediated by age-related improvements in foraging expertise and increased competitiveness developed during maturation. Thus, landfill use is shaping foraging strategies and species behaviour from an early age, with potential consequences for population dynamics

Balancing structural complexity with ecological insight in Spatio‐temporal species distribution models

1. The potential for statistical complexity in species distribution models (SDMs) has greatly increased with advances in computational power. Structurally complex models provide the flexibility to analyse intricate ecological systems and realistically messy data, but can be difficult to interpret, reducing their practical impact. Founding model complexity in ecological theory can improve insightgained from SDMs. 2. Here, we evaluate a marked point process approach, which uses multiple Gaussian random fields to represent population dynamics of the Eurasian crane Grus grus in a spatio-temporal species distribution model. We discuss the role of model components and their impacts on predictions, in comparison with a simpler binomial presence/absence approach. Inference is carried out using Integrated Nested Laplace Approximation (INLA) with inlabru, an accessible and computationally efficient approach for Bayesian hierarchical modelling, which is not yet widely used in SDMs. 3. Using the marked point process approach, crane distribution was predicted to be dependent on the density of suitable habitat patches, as well as close to observations of the existing population. This demonstrates the advantage of complex model components in accounting for spatio-temporal population dynamics (such as habitat preferences and dispersal limitations) that are not explained by environmental variables. However, including an AR1 temporal correlation structure in the models resulted in unrealistic predictions of species distribution; highlighting the need for careful consideration when determining the level of model complexity. 4. Increasing model complexity, with careful evaluation of the effects of additional model components, can provide a more realistic representation of a system, which is of particular importance for a practical and impact-focused discipline such as ecology (though these methods extend to applications for a wide range of systems). Founding complexity in contextual theory is not only fundamental to maintaining model interpretability but can be a useful approach to improving insight gained from model outputs

Balancing structural complexity with ecological insight in Spatio‐temporal species distribution models

1. The potential for statistical complexity in species distribution models (SDMs) has greatly increased with advances in computational power. Structurally complex models provide the flexibility to analyse intricate ecological systems and realistically messy data, but can be difficult to interpret, reducing their practical impact. Founding model complexity in ecological theory can improve insightgained from SDMs. 2. Here, we evaluate a marked point process approach, which uses multiple Gaussian random fields to represent population dynamics of the Eurasian crane Grus grus in a spatio-temporal species distribution model. We discuss the role of model components and their impacts on predictions, in comparison with a simpler binomial presence/absence approach. Inference is carried out using Integrated Nested Laplace Approximation (INLA) with inlabru, an accessible and computationally efficient approach for Bayesian hierarchical modelling, which is not yet widely used in SDMs. 3. Using the marked point process approach, crane distribution was predicted to be dependent on the density of suitable habitat patches, as well as close to observations of the existing population. This demonstrates the advantage of complex model components in accounting for spatio-temporal population dynamics (such as habitat preferences and dispersal limitations) that are not explained by environmental variables. However, including an AR1 temporal correlation structure in the models resulted in unrealistic predictions of species distribution; highlighting the need for careful consideration when determining the level of model complexity. 4. Increasing model complexity, with careful evaluation of the effects of additional model components, can provide a more realistic representation of a system, which is of particular importance for a practical and impact-focused discipline such as ecology (though these methods extend to applications for a wide range of systems). Founding complexity in contextual theory is not only fundamental to maintaining model interpretability but can be a useful approach to improving insight gained from model outputs

Relative abundance and distribution of fisheries influence risk of seabird bycatch

Fisheries provide an abundant and predictable food source for many pelagic seabirds through discards, but also pose a major threat to them through bycatch, threatening their populations worldwide. The reform of the European Common Fisheries Policy (CFP), which intends to ban discards through the landing obligation of all catches, may force seabirds to seek alternative food sources, such as baited hooks from longlines, increasing bycatch rates. To test this hypothesis we performed a combined analysis of seabird-fishery interactions using as a model Scopoli's shearwaters Calonectris diomedea in the Mediterranean. Tracking data showed that the probability of shearwaters attending longliners increased exponentially with a decreasing density of trawlers. On-board observations and mortality events corroborated this result: the probability of birds attending longliners increased 4% per each trawler leaving the longliner proximity and bird mortality increased tenfold when trawlers were not operating. Therefore, the implementation of the landing obligation in EU waters will likely cause a substantial increase in bycatch rates in longliners, at least in the short-term, due to birds switching from trawlers to longliners. Thus the implementation of the landing obligation must be carefully monitored and counterbalanced with an urgent implementation of bycatch mitigation measures in the longline fleet

How salinity and temperature combine to affect physiological state and performance in red knots with contrasting non-breeding environments

Migratory shorebirds inhabit environments that may yield contrasting salinity-temperature regimes-with widely varying osmoregulatory demands, even within a given species-and the question is: by which physiological means and at which organisational level do they show adjustments with respect to these demands? Red knots Calidris canutus winter in coastal areas over a range of latitudes. The nominal subspecies winters in salty areas in the tropics, whereas the subspecies Calidris canutus islandica winters in north-temperate regions of comparatively lower salinities and temperatures. In this study, both subspecies of red knot were acclimated to different salinity (28/40 ‰)-temperature (5/35 °C) combinations for 2-week periods. We then measured food/salt intakes, basal metabolic rate (BMR), body mass and temperature, fat and salt gland scores, gizzard mass, heat-shock proteins, heterophils/lymphocytes (H/L) ratio and plasma Na(+) to assess the responses of each taxon to osmoregulatory challenges. High salinity (HS)-warm-acclimated birds reduced food/salt intake, BMR, body mass, fat score and gizzard mass, showing that salt/heat loads constrained energy acquisition rates. Higher salt gland scores in saltier treatments indicated that its size was adjusted to higher osmoregulatory demands. Elevated plasma Na(+) and H/L ratio in high-salinity-warm-acclimated birds indicated that salt/heat loads might have a direct effect on the water-salt balance and stress responses of red knots. Subspecies had little or no effect on most measured parameters, suggesting that most adjustments reflect phenotypic flexibility rather than subspecific adaptations. Our results demonstrate how salinity and temperature affect various phenotypic traits in a migrant shorebird, highlighting the importance of considering these factors jointly when evaluating the environmental tolerances of air-breathing marine taxa

Testing alternative methods for estimation of bird migration phenology from GPS tracking data

The development and miniaturization of GPS tracking devices has enabled a better understanding of migration phenology, but it can be challenging to identify where and when migration starts and ends, and researchers rely on multiple methods to infer it. Here, we use GPS tracks of 18 trans-Saharan migrant White Storks Ciconia ciconia to determine how the choice of method influences the estimation of migratory timing and discuss its implications. We evaluate and provide R code for the implementation of five alternative methods: spatial threshold, absolute displacement, spatio-temporal displacement, net squared displacement and change point analysis. Spatial threshold, absolute displacement and spatio-temporal displacement methods produce, in most cases, significantly different estimates of migration timing and duration as compared with net squared displacement and change point analysis

Digital data sources and methods for conservation culturomics

Peer reviewe