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Onderzoek - In opdracht van de Gemeente Amsterdam, Gemeente Diemen en Provincie Noord-Holland, hebben onderzoekers van het Instituut voor Biodiversiteit en Ecosysteem Dynamica (IBED) vogeltrek in kaart gebracht met verschillende radartechnieken. Het onderzoek heeft zich toegespitst op twee vragen die relevant zijn voor windenergie. 1. Wat is de vlieghoogte van trekvogels? 2. Wat is de ruimtelijke verspreiding van vogeltrek boven Noord-Holland? Voor de algemene inspanningen die gedaan worden om aanvaringen tussen trekkende vogels en windturbines tegen te gaan, waarbij geen onderscheid gemaakt wordt tussen verschillende soorten of soortgroepen, is een focus op de nachtelijk trek in het najaar het meest efficiënt.

To achieve the goals of the 2030 Global Biodiversity Framework, the European Biodiversity Strategy, and the EU Green Deal, biodiversity monitoring is critical. Monitoring efforts in Europe, however, suffer from gaps and biases in taxonomy, spatial coverage, and temporal resolution, resulting in fragmented and disconnected data. To assess user and policy needs in biodiversity monitoring, we employed a four-step user-centered stakeholder engagement process with over 300 stakeholders including a public stakeholder workshop, online survey, interviews, and a meeting with experts from 18 EU member states, the European Commission, and the European Environment Agency. The stakeholders identified policy needs, current challenges, and potential solutions. Based on the policy and stakeholder assessment, we recommend establishing a European Biodiversity Observation Coordinating Centre to optimize existing observation efforts, harmonize data, and enhance our ability to predict and respond to key challenges related to biodiversity loss in Europe.

In this report, we present the analysis of the different available biodiversity data streams at the EU and national level, both baseline biodiversity data and monitoring data. We assess how these biodiversity data inform and trigger policy action and identify the related challenges the different European countries and relevant EU agencies face and the solutions to overcome them. To do this, we consulted with more than 350 expert stakeholders from policy, research and practice. The assessment identified a fragmented biodiversity data landscape that cannot currently easily answer all relevant policy questions. Quantity and quality of biodiversity baseline datasets differ for the different countries, ranging from non-existent biodiversity monitoring due to capacity issues, to regular monitoring of ecosystem processes and state. By engaging stakeholders and experts in both member states and non-member states and from several EU bodies, we identified key challenges and ways to address these with targeted solutions towards building a joint European Biodiversity Monitoring Network. Solutions include focussing on cooperation and coordination, enhanced data standardisation and sharing, as well as the use of models and new technologies. These solutions can however only be realised with dedicated funding and capacity building, in coordination with all stakeholders in partnership.

•Capsule: Strong individual variation was observed in the responses of Black-legged Kittiwakes Rissa tridactyla to environmental covariates related to foraging behaviour and habitat selection, and in the overlap with nearby offshore windfarms (OWFs). •Aims: To determine whether environmental covariates consistently drive Kittiwake foraging behaviour and how this may influence overlap with local potential stressors at the population and individual levels. •Methods: We used two complimentary methods (Hidden Markov Models and Step Selection Functions) to classify the at-sea behaviour of Kittiwakes and identify environmental covariates associated with foraging at a colony in northeast Scotland during the 2021 breeding season. We also calculated the overlap, by behaviour, of individuals with several operational and proposed OWFs within the vicinity. •Results: We found no evidence for habitat selection at the population level, with uncertainty in which conditions were linked to foraging, due to considerable variation in the responses of individuals to local environmental conditions. This was attributed to unmeasured intrinsic variation among individuals and high competition among conspecifics and other seabird species. We also observed variation among individuals in the extent of overlap with a local stressor, OWFs, by behaviour. •Conclusion: Individuals within a population that do not respond consistently to environmental conditions will likely vary in their vulnerability to local stressors, in this case to OWFs. This could lead to unforeseen population-level consequences if not accounted for. Therefore, it is important to identify and understand variation among individuals to better establish population-level consequences of different foraging areas and overlap with stressors to reduce uncertainty in current impact assessments.

Seasonal migrations are used by diverse animal taxa, yet the costs and benefits of migrating have rarely been empirically examined. The aim of this study was to determine how migration influences two ecological currencies, energy expenditure and time allocated towards different behaviors, in a full annual cycle context. We compare these currencies among lesser black-backed gulls that range from short- (< 250 km) to long-distance (> 4500 km) migrants. Daily time-activity budgets were reconstructed from tri-axial acceleration and GPS, which, in conjunction with a bioenergetics model to estimate thermoregulatory costs, enabled us to estimate daily energy expenditure throughout the year. We found that migration strategy had no effect on annual energy expenditure, however, energy expenditure through time deviated more from the annual average as migration distance increased. Patterns in time-activity budgets were similar across strategies, suggesting migration strategy does not limit behavioral adjustments required for other annual cycle stages (breeding, molt, wintering). Variation among individuals using the same strategy was high, suggesting that daily behavioral decisions (e.g. foraging strategy) contribute more towards energy expenditure than an individual’s migration strategy. These findings provide unprecedented new understanding regarding the relative importance of fine versus broad-scale behavioral strategies towards annual energy expenditures.

In this report, we present the analysis of the different available biodiversity data streams at the EU and national level, both baseline biodiversity data and monitoring data. We assess how these biodiversity data inform and trigger policy action and identify the related challenges the different European countries and relevant EU agencies face and the solutions to overcome them. To do this, we consulted with more than 350 expert stakeholders from policy, research and practice. The assessment identified a fragmented biodiversity data landscape that cannot currently easily answer all relevant policy questions. Quantity and quality of biodiversity baseline datasets differ for the different countries, ranging from non-existent biodiversity monitoring due to capacity issues, to regular monitoring of ecosystem processes and state. By engaging stakeholders and experts in both member states and non-member states and from several EU bodies, we identified key challenges and ways to address these with targeted solutions towards building a joint European Biodiversity Monitoring Network. Solutions include focussing on cooperation and coordination, enhanced data standardisation and sharing, as well as the use of models and new technologies. These solutions can however only be realised with dedicated funding and capacity building, in coordination with all stakeholders in partnership.

Migrating animals show remarkable diversity in migration strategies, even between individuals from the same population. Migrating longer distances is usually expected to be costlier in terms of time, energy expenditure and risks with potential repercussions for subsequent stages within the annual cycle. Such costs are expected to be balanced by increased survival, for example due to higher quality wintering areas or lower energy expenditure at lower latitudes. We compared reproductive parameters and apparent survival of lesser black-backed gulls (Larus fuscus) breeding in The Netherlands, whose winter range extends from the UK to West Africa, resulting in one-way migration distances that differ by more than 4500 km. Individuals migrating furthest arrived later in the colony than shorter distance migrants, but still laid in synchrony with the colony and consequently had a shorter pre-laying period. This shorter pre-laying period affected neither egg volumes nor hatching success. We found no relationship between migration distance and apparent survival probability, corresponding with previous research showing that annual energy expenditure and distance travelled throughout the year is similar across migration strategies. Combined, our results indicate an equal fitness payoff across migration strategies, suggesting there is no strong selective pressure acting on migration strategy within this population.

Demographic rates such as recruitment and survival probability can vary considerably among populations of the same species due to variation in underlying environmental processes. If environmental processes are spatially correlated, nearby populations are expected to have more similar demographic rates than those further apart. Breeding populations and foraging ranges are spatially segregated in colonial seabirds, making them ideal for studying spatial patterns in demographic rates and their effects on local population dynamics. Here we explored variation in age-dependentsurvival probabilities across 14 colonies of Herring Gulls Larus argentatus breeding along the Dutch North Sea coast. We used long-term mark–recapture data of marked fledglings to estimate survival, and estimated spatial autocorrelation of survival probabilities. We assessed whether survival until recruitment age or until 10 years old (close to their expected lifespan) explained variation in population trajectories of each colony. Juvenile and adult survival showed a strong, but different, north-to-south gradient in survival probability, with lower juvenile but higher adult survival in northern colonies than southern colonies, whereas the spatial pattern of immature survival was less distinct. Neither recruitment nor the proportion of 10-year-old adults alive predicted whether a colony collapsed, declined, remained stable or increased. The distinct spatial pattern in survival suggests variation in regional food availability, which do not seem to drive local population dynamics. The absence of a link between survival and colony trajectories implies that connectivity between populations plays an important role affecting population dynamics.

The population increase of Lesser Black-backed Gulls in The Netherlands triggered investigations into life-history, migratory movements and foraging ecology during 16 years of nest-monitoring, colour-ringing and GPS-tracking on the island of Texel (Wadden Sea). The main objective was to obtain comprehensive ecological data on breeding performance within the context of the annual cycle, shifts in resources, prey types and habitat use. Migration strategies ranged from short- (France, England), medium- (Portugal, Spain) to long-distance (NW Africa), utilising marine, coastal or terrestrial, region-specific resources. Young birds travelled on average further than older individuals. Strong within-colony philopatry was found, this was strongest in males. Assessments of mate-fidelity indicated serial, social monogamy. Unexpectedly, given increasing population trends when the study commenced, fledging rates were low and declining egg volumes, smaller hatchlings, declining mass at fledging and high levels of cannibalism indicated structural food stress. Fledgling mass was well below that of chicks in historical studies, suggesting insufficient provisioning. Breeding was highly synchronised and early nesters fledged more young than late pairs. The onset of breeding was significantly delayed over the years, chick depredation rates declined, overall breeding success became more variable. Marine, urban and rural habitats, mostly within 80 km from the colony were used for foraging. Marine prey, mostly fisheries discards, formed the principal prey for most birds, supplemented with food found in agricultural areas. Human waste was found in only 7% of prey samples. A consistent decline of marine prey (in line with developing restrictions in fisheries), combined with signals pointing at food stress, suggests that the population is unable to boost reproductive success with currently existing foraging opportunities.

Current biodiversity monitoring in Europe is fragmented and often inconsistent across countries. Monitoring efforts face multiple challenges including insufficient technical and human capacity, limited funding, data unavailability, and lack of long-term policy support. To address these challenges, the Europa Biodiversity Observation Network (EuropaBON) proposes five clusters of solutions to improve the collection and uptake of policy-relevant biodiversity data: - Enhance coordination and collaboration of monitoring efforts by identifying priorities, using standardized protocols, and aligning reporting requirements with specific indicators. - Increase data standardization through the combination of Essential Biodiversity and Essential Ecosystem Services Variables (EBVs and EESVs) with dedicated data sharing and exchange mechanisms that adhere to open and FAIR (findable, accessible, interoperable, and reusable) principles. - Leverage modeling efforts and new technologies to integrate with traditional monitoring methods. - Enable additional, consistent, and long-term financial resources for monitoring efforts, including more and better coordination across countries, institutions, and sectors, along with privatesector investments. - Expand, adapt, and deliver capacity building, such as expert training, creating new exchange knowledge platforms, and embracing citizen science initiatives. We propose the creation of a European Biodiversity Monitoring Coordination Centre in the near future to implement lasting improvements in the collection, analysis, reporting, and political uptake of biodiversity data in all European countries.

Demographic rates such as recruitment and survival probability can vary considerably among populations of the same species due to variation in underlying environmental processes. If environmental processes are spatially correlated, nearby populations are expected to have more similar demographic rates than those further apart. Breeding populations and foraging ranges are spatially segregated in colonial seabirds, making them ideal for studying spatial patterns in demographic rates and their effects on local population dynamics. Here we explored variation in age-dependentsurvival probabilities across 14 colonies of Herring Gulls Larus argentatus breeding along the Dutch North Sea coast. We used long-term mark–recapture data of marked fledglings to estimate survival, and estimated spatial autocorrelation of survival probabilities. We assessed whether survival until recruitment age or until 10 years old (close to their expected lifespan) explained variation in population trajectories of each colony. Juvenile and adult survival showed a strong, but different, north-to-south gradient in survival probability, with lower juvenile but higher adult survival in northern colonies than southern colonies, whereas the spatial pattern of immature survival was less distinct. Neither recruitment nor the proportion of 10-year-old adults alive predicted whether a colony collapsed, declined, remained stable or increased. The distinct spatial pattern in survival suggests variation in regional food availability, which do not seem to drive local population dynamics. The absence of a link between survival and colony trajectories implies that connectivity between populations plays an important role affecting population dynamics.

In animal ecology, energy expenditure is used for assessing the consequences of different behavioural strategies, life-history events or environments. Animals can also influence energy expenditure through instantaneous behavioural responses to their external environment. It is therefore of interest to measure energy expenditure of free-ranging animals across seasons and at high temporal resolutions. Heart rate has historically been used for this, but requires invasive surgery for long-term use. Dynamic body acceleration (DBA) is an alternative proxy for energy expenditure that is simpler to deploy, yet few studies have examined how it performs over extended time periods, or for species using different locomotory modes, especially passive modes like soaring flight.We measured DBA alongside heart rate in free-ranging lesser black-backed gulls, a seabird that moves using flapping flight, soaring and walking, and rests on both land and water. Our objectives were to compare the relative changes in DBA and heart rate among and within behaviours and to examine how accelerometers can be used to estimate daily energy expenditure by comparing DBA to time-energy budgets (TEBs).DBA and heart rate were sampled concurrently at 2.5- and 5-min intervals throughout the breeding season, though measurements were not exactly synchronised. Behaviour was identified from accelerometer measurements, and DBA and heart rate were averaged over bouts of consistent behaviour. Heart rate was converted to metabolic rate using an allometric calibration, after confirming its fit using metabolic measurements taken in captivity and values from existing literature.Both proxies showed similar changes among behaviours, though DBA overestimated costs of floating, likely due to waves. However, relationships between DBA and heart rate were weak within a behaviour mode, possibly due to the lack of synchrony between proxy measurements.On daily scales, DBA and TEBs perform comparably for estimating daily ener

Observations are key to understand the drivers of biodiversity loss, and the impacts on ecosystem services and ultimately on people. Many EU policies and initiatives demand unbiased, integrated and regularly updated biodiversity and ecosystem service data. However, efforts to monitor biodiversity are spatially and temporally fragmented, taxonomically biased, and lack integration in Europe. EuropaBON aims to bridge this gap by designing an EU-wide framework for monitoring biodiversity and ecosystem services. EuropaBON harnesses the power of modelling essential variables to integrate different reporting streams, data sources, and monitoring schemes. These essential variables provide consistent knowledge about multiple dimensions of biodiversity change across space and time. They can then be analyzed and synthesized to support decision-making at different spatial scales, from the sub-national to the European scale, through the production of indicators and scenarios. To develop essential biodiversity and ecosystem variables workflows that are policy relevant, EuropaBON is built around stakeholder engagement and knowledge exchange (WP2). EuropaBON will work with stakeholders to identify user and policy needs for biodiversity monitoring and investigate the feasibility of setting up a center to coordinate monitoring activities across Europe (WP2). Together with stakeholders, EuropaBON will assess current monitoring efforts to identify gaps, data and workflow bottlenecks, and analyse cost-effectiveness of different schemes (WP3). This will be used to co-design improved monitoring schemes using novel technologies to become more representative temporally, spatially and taxonomically, delivering multiple benefits to users and society (WP4). Finally, EuropaBON will demonstrate in a set of showcases how workflows tailored to the Birds Directive, Habitats Directive, Water Framework Directive, Climate and Restoration Policy, and the Bioeconomy Strategy, can be implemented (WP5).

In this report, we present the analysis of the different available biodiversity data streams at the EU and national level, both baseline biodiversity data and monitoring data. We assess how these biodiversity data inform and trigger policy action and identify the related challenges the different European countries and relevant EU agencies face and the solutions to overcome them. To do this, we consulted with more than 350 expert stakeholders from policy, research and practice. The assessment identified a fragmented biodiversity data landscape that cannot currently easily answer all relevant policy questions. Quantity and quality of biodiversity baseline datasets differ for the different countries, ranging from non-existent biodiversity monitoring due to capacity issues, to regular monitoring of ecosystem processes and state. By engaging stakeholders and experts in both member states and non-member states and from several EU bodies, we identified key challenges and ways to address these with targeted solutions towards building a joint European Biodiversity Monitoring Network. Solutions include focussing on cooperation and coordination, enhanced data standardisation and sharing, as well as the use of models and new technologies. These solutions can however only be realised with dedicated funding and capacity building, in coordination with all stakeholders in partnership.

In this report, we present the analysis of the different available biodiversity data streams at the EU and national level, both baseline biodiversity data and monitoring data. We assess how these biodiversity data inform and trigger policy action and identify the related challenges the different European countries and relevant EU agencies face and the solutions to overcome them. To do this, we consulted with more than 350 expert stakeholders from policy, research and practice. The assessment identified a fragmented biodiversity data landscape that cannot currently easily answer all relevant policy questions. Quantity and quality of biodiversity baseline datasets differ for the different countries, ranging from non-existent biodiversity monitoring due to capacity issues, to regular monitoring of ecosystem processes and state. By engaging stakeholders and experts in both member states and non-member states and from several EU bodies, we identified key challenges and ways to address these with targeted solutions towards building a joint European Biodiversity Monitoring Network. Solutions include focussing on cooperation and coordination, enhanced data standardisation and sharing, as well as the use of models and new technologies. These solutions can however only be realised with dedicated funding and capacity building, in coordination with all stakeholders in partnership.

The expanding development of offshore wind farms brings a growing concern about the human impact on seabirds. To assess this impact a better understanding of offshore bird abundance is needed. The aim of this study was to investigate offshore bird abundance in the breeding season and model the effect of temporally predictable environmental variables. We used a bird radar, situated at the edge of a wind farm (52.427827° N, 4.185345° E), to record hourly aerial bird abundance at the North Sea near the Dutch coast between May 1st and July 15th in 2019 and 2020, of which 1879 h (51.5%) were analysed. The effect of sun azimuth, week in the breeding season, and astronomic tide was evaluated using generalized additive modelling. Sun azimuth and week in the breeding season had a modest and statistically significant (p < 0.001) effect on bird abundance, while astronomic tide did not. Hourly predicted abundance peaked after sunrise and before sunset, and abundance increased throughout the breeding season until the end of June, after which it decreased slightly. Though these effects were significant, a large portion of variance in hourly abundance remained unexplained. The high variability in bird abundance at scales ranging from hours up to weeks emphasizes the need for long-term and continuous data which radar technology can provide.

Non‐frugivorous waterbirds disperse a wide variety of plants by endozoochory, providing longer‐dispersal distances than other mechanisms. Many waterbirds visit both agricultural and natural landscapes during their daily movements, but potential bird‐mediated dispersal of weed plants within and from agricultural landscapes to other habitats is commonly overlooked. Gulls (Laridae) are expanding in numbers and increasingly exploiting anthropogenic habitats worldwide, with possible growing implications for the spread of weeds. Yet, to date, there are no studies on the spatial distribution of weed dispersal by waterbirds. We developed a plant dispersal model based on movements of 19 Larus fuscus using ricefields, via GPS telemetry. We combined daily movements with two curves estimating the retention times of plant seeds in their guts: (a) an experimental curve based on retention time in captivity for four weeds with dry fruits known to be dispersed by gulls: Juncus bufonius, Cyperus difformis, Polypogon monspeliensis and the alien Amaranthus retroflexus; (b) a theoretical curve based on the interspecific scaling relationship between body mass and mean retention time. Median dispersal distances of weed plant seeds by gulls ranged between 690 and 940 m, but maximum distances exceeded 150 km. The theoretical retention time model showed higher median dispersal distances than the experimental retention time model. Spatial patterns of weed deposition were very similar between retention time methods, and most strongly depended on gull movements. Variation between individual gulls had little influence on seed shadows. About 92% of all seeds (>10,000 intact seeds per day) were dispersed within the ricefield area of 370 km2. The remaining 8% of seeds were deposited beyond ricefields into other habitats, 42% of which reached moist environments (other irrigated agriculture, rivers and natural wetlands) presumably s

CapsuleMigration studies of tagged Eurasian Bitterns Botaurus stellaris provide information on the behaviour of this secretive species in relation to weather conditions.AimsTo study if cold spells trigger southward migration in resident Eurasian Bitterns. To describe migratory behaviour including flight routes, altitudes, flight direction in relation to wind speed and direction, and general characteristics of stopping sites.MethodsSix adult Eurasian Bitterns from Dutch breeding areas were followed for two to five years using ARGOS-PTT/GPS transmitters or GPS trackers.ResultsFour individuals remained at the breeding sites in winter and did not migrate in response to cold spells. Two individuals covered distances of 300 and 1600 km between stopping sites. They migrated predominantly at night, but over the Sahara they extended flights into daylight hours. Depending on wind assistance, flight speeds (groundspeed) varied between 3.6 and 26 ms−1. Flight altitude varied from just above sea level when facing headwinds, to almost 2000 m above sea level under tail wind conditions. Repeatedly tracked individuals showed substantial variation in routes and stopping sites between successive migrations. These flight patterns appeared influenced by the speed and direction of the winds encountered en route.ConclusionsEurasian Bitterns were either migratory or resident and the latter individuals did not perform facultative movements at the onset of cold spells. The flight speed, flight altitudes, and routes of migrating birds were influenced by wind conditions. This likely explains the variable use of stopping sites between years.

Many populations consist of individuals that differ consistently in their foraging behaviour through resource or foraging site selection. Foraging site fidelity has been reported in several seabird species as a common phenomenon. It is considered especially beneficial in spatially and/or temporally predictable environments in which fidelity is thought to increase energy intake, thereby affecting time‐energy budgets. However, the consequences for activity and energy budget have not been adequately tested. In this paper, we studied the consequences of fine‐scale foraging site fidelity in adult Herring Gulls Larus argentatus in a highly predictable foraging environment with distinct foraging patches. We measured their time‐activity budgets using GPS tracking and tri‐axial acceleration measurements, which also made it possible to estimate energy expenditure. Individual variation in foraging site fidelity was high, some individuals spending most of their time on a single foraging patch and others spending the same amount of time in up to 21 patches. While time and activity budgets differed between individuals, we found no clear relationship with foraging site fidelity. We did find a relationship between the size of the birds and the level of site fidelity; faithful birds tend to have a larger body size. Although differences in foraging time and habitat use between individuals could play a role in the results of the current study, short‐term consequences of variation in foraging site fidelity within a population remain elusive, even when focusing on individuals with a similar foraging specialization (Blue Mussels Mytilus edulis). Studying individuals over multiple years and under varying environmental conditions may provide better insight into the consequences and plasticity of foraging site fidelity.

BackgroundSeveral generalist species benefit from food provided by human activities. Food from anthropogenic sources is often high in caloric value and can positively influence reproductive success or survival. However, this type of resource may require specific foraging skills and habitat experience with related costs and benefits. As a result, not all individuals utilize these resources equally, with some individuals preferentially foraging in habitats where natural resources of lower energy content are predominant, possibly due to lower energy expenditure of the specific foraging strategy.MethodsHere we investigate whether foraging in habitats which contain high caloric resources of anthropogenic origin is energetically costlier than foraging in habitats with low caloric resources such as intertidal areas or agricultural and natural areas, for example due to increased flight costs, in a generalist seabird, the herring gull Larus argentatus. We use data from GPS trackers with tri-axial acceleration measurements that allow us to quantify time-energy budgets, representing energy expenditure during foraging trips of herring gulls for each habitat.ResultsWe show that the rate of energy expenditure is on average 34% higher when individuals forage for high caloric prey in marine and urban areas compared to foraging for low caloric prey in intertidal and agricultural areas. Energetic estimates suggest that if birds would feed completely on these resources, they have to gather ~ 400 kJ per day more to compensate for the higher foraging costs.ConclusionsEnergy expenditure differs among foraging habitat and may thereby influence foraging decisions of individual herring gulls. As management of anthropogenic resources changes, so too may the costs and potential benefits of foraging strategies which are strongly tied to human activities.

Interactions between landscape and atmosphere result in a dynamic flight habitat which birds may use opportunistically to save energy during flight. However, their ability to utilise these dynamic landscapes and its influence on shaping movement paths is not well understood. We investigate the degree to which gulls utilise fine scale orographic lift created by wind deflected upwards over landscape features in a virtually flat landscape. Using accelerometer measurements and GPS tracking, soaring flight is identified and analysed with respect to orographic lift, modelled using high-resolution digital elevation models and wind measurements. The relationship between orographic lift and flight routes suggests gulls have advanced knowledge of their aerial surroundings and the benefits to be gained from them, even regarding small features such as tree lines. We show that in a landscape constantly influenced by anthropogenic change, the structure of our landscape has an aerial impact on flight route connectivity and costs.

In many bird species intraspecific variation in migration strategies is related tosex or size. The Eurasian Bittern Botaurus stellaris is a sexually size-dimorphicheron species with a vast breeding and wintering range spanning a range ofclimates. Ringing data show that Bitterns from northern populations migratewestwards or southwards over thousands of kilometres, while Bitterns fromsouthern or temperate breeding areas migrate much shorter distances or remainresident. So far, any differences in the migrations of males and females haveremained unstudied. In temperate climates, relatively benign winters alternatewith the occasional harsh winter, and under these conditions, males as thelarger sex might take the risk to stay rather than show seasonal migration. In theyears 2010–2012 we equipped three females and three males from breedingareas in The Netherlands with a tracking device, recording their movementsover periods of 2–5 years. All three males and one female stayed within or nearthe breeding area during the non-breeding season, but two females moved todistant wintering sites. One female migrated 4900 km to The Gambia providingthe first direct evidence for trans-Saharan migration in this species. Anotherfemale migrated 700 km to winter in Devon, UK, for five consecutive years. TheBitterns were site-faithful to their breeding area and, mostly, to their winteringareas as well, although one male and one female progressively wintered closerto the breeding area in three successive years. Our results suggest that largermales from The Netherlands, a breeding area with fluctuating winter conditions,are predominantly resident, while the females are partial migrants with individuallydifferent and flexible strategies.

1.Eutrophication of aquatic ecosystems is a global problem with major ecological and economic impacts. In many lakes and reservoirs, guanotrophication occurs when roosting waterbirds import nutrients (nitrogen and phosphorus) from surrounding terrestrial habitats. To date, nutrient loading by waterbirds has been estimated based on censuses in the absence of detailed information on their movements. We quantified nutrient importation by the lesser black‐backed gull (Larus fuscus) to Fuente de Piedra (1,350 ha) in Andalusia (south‐west Spain), where an average of 36,288 individuals are counted in January. 2.During seven winters from 2010 to 2017, we used movement data from 20 individual gulls tagged with Global Positioning System trackers that foraged in four landfills. Together with monthly bird counts and measurements of total N and P content in faeces and pellet samples, movement data were used to quantify the total external loading effect for different winters. Movement data allowed us to quantify the proportion of time spent in the lake and the time spent at different foraging sites and enabled correction of censuses.3.According to tracking data, on average 69% of the birds had already left the lake to head for feeding sites when waterbird counts were carried out. Nutrient inputs to the lake depend partly on the proportion of the day that gulls spend there, which was higher in late winters and was reduced when lake depth went below or above 20–35 cm. An estimated average of 10.17 kg N ha−1 year−1 and 2.07 kg P ha−1 year−1 were imported to this closed‐basin lake by gulls each winter, with highest values recorded in winter 2016–2017. 4.Gull guano is the most important winter source of nutrients to the lake. Regurgitated pellets have been ignored as a source of nutrients in other guanotrophy studies, but we found them to be a more important source of P than faeces. A movement ecology approach complements traditional

© 2018 The Authors Nocturnal avian migration flyways remain an elusive concept, as we have largely lacked methods to map their full extent. We used the network of European weather radars to investigate nocturnal bird movements at the scale of the European flyway. We mapped the main migration directions and showed the intensity of movement across part of Europe by extracting biological information from 70 weather radar stations from northern Scandinavia to Portugal, during the autumn migration season of 2016. On average, over the 20 nights and all sites, 389 birds passed per 1 km transect per hour. The night with highest migration intensity showed an average of 1621 birds km–1 h–1 passing the radar stations, but there was considerable geographical and temporal variation in migration intensity. The highest intensity of migration was seen in central France. The overall migration directions showed strong southwest components. Migration dynamics were strongly related to synoptic wind conditions. A wind-related mass migration event occurred immediately after a change in wind conditions, but quickly diminished even when supporting winds continued to prevail. This first continental-scale study using the European network of weather radars demonstrates the wealth of information available and its potential for investigating large-scale bird movements, with consequences for ecosystem function, nutrient transfer, human and livestock health, and civil and military aviation.

Dietary specialization has been described across a wide range of taxa in the animal kingdom. Fitness consequences are, however, not well documented. We examined the reproductive consequences of different dietary specializations in the herring gull Larus argentatus, an omnivorous seabird, using an extensive dataset which includes breeding and dietary data of 10 successive years. We hypothesized that pairs that focused on prey of higher energetic value would yield higher fledging rates. An alternative hypothesis is that pairs that relied on more resources simultaneously would reproduce better. The novelty of this study is that we used continuous measurements representing dietary composition and degree of specialization rather than restricting our analysis to predefined categories. By relating these two continuous measurements for diet to several proxies for reproductive success, we show clear consequences of dietary choice. Most pairs concentrated on bivalves, a prey type not particularly rich in energy. Pairs feeding on energy-rich prey (e.g., “domestic refuse and fishery discards”) during chick rearing were found to have a higher reproductive success, supporting the first hypothesis. Pairs that used more resources did not clearly have a higher reproductive success. The majority of the pairs did not switch to energy-rich prey during chick rearing, despite low breeding outcome. We discuss how trade-offs between factors such as resource availability, predictability, and the time and energy needed to obtain certain prey species may influence resource selection.

The aerial environment is heterogeneous in space and time and directly influences the costs of animal flight. Volant animals can reduce these costs by using different flight modes, each with their own benefits and constraints. However, the extent to which animals alter their flight modes in response to environmental conditions has rarely been studied in the wild. To provide insight into how a flight generalist can reduce the energetic cost of movement, we studied flight behaviour in relation to the aerial environmental and landscape using hundreds of hours of global positioning system and triaxial acceleration measurements of the lesser black-backed gull (Larus fuscus). Individuals differed largely in the time spent in flight, which increased linearly with the time spent in flight at sea. In general, flapping was used more frequently than more energetically efficient soaring flight. The probability of soaring increased with increasing boundary layer height and time closer to midday, reflecting improved convective conditions supportive of thermal soaring. Other forms of soaring flight were also used, including fine-scale use of orographic lift. We explore the energetic consequences of behavioural adaptations to the aerial environment and underlying landscape and implications for individual energy budgets, foraging ecology and reproductive success.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.

Recent developments in GPS tracking technology allow the movements of bird species to be followed in ever-greater detail. Seabird research is benefiting greatly, due to the challenges of tracking species that often roam widely out at sea. Amongst the gulls, one of the pressing issues is to understand the ecology of the relatively recent urban colonists and how they differ from their counterparts in traditional rural colonies. Here, we present what we believe are the first GPS results from roof-nesting gulls. Four adult Herring Gulls (two males, two females) were fitted with GPS tags in May 2014 in the seaside town of St Ives, Cornwall (breeding colony c 250 pairs), and tracked for c 100 days during the 2014 breeding season. We estimated the home ranges of the four individuals and how their movement behaviour varied through the 24-h period and across the breeding season. The results highlight how variable movement behaviour was among individuals: whilst one bird roamed widely (90% range estimate = 560 km2), heading >50 km offshore and often active at night or roosting at sea, two birds had small ranges (<10 km2), always attended the colony at night and rarely headed more than a few hundred metres offshore, with the fourth displaying intermediate behaviour. All of the birds regularly utilised a few key sites within the agricultural landscape south of St Ives. Whilst this study was too small to allow general conclusions to be drawn about urban Herring Gulls, it reinforces how variable individual behaviour can be amongst the large gulls and will be particularly interesting when applied to a larger sample of birds, especially in big urban gull colonies further inland.

While seabird–fishery associations are well documented, this research primarily comes from ship-based surveys and consequently individual level responses to discard availability are largely unknown. As part of a long-term study on lesser black-backed gulls (Larus fuscus) in the Netherlands, the fine-scale movements of adults were tracked with GPS tags throughout the breeding period. The aim of this study was to determine if lesser black-backed gulls were utilizing fishery discards in the Wadden Sea and to examine possible consequences of this behaviour. Within the Wadden Sea during weekdays, tracked birds predominately associated with zones where fishing vessels are known to operate (deep gullies). Across all individuals combined (n = 40), there was a significantly reduced use of the Wadden Sea during weekends when the fleets were not operating. Eight females, who markedly increased their use of the Wadden Sea during weekdays throughout the breeding period, were largely responsible for this pattern. The loss of discard resources on weekends primarily resulted in these eight individuals switching to terrestrial foraging areas. Nest attendance and total foraging time were consistent between weekdays and weekends, suggesting that resource shifts on weekends did not impact daily time budgets. As such, it appears that lesser black-backed gulls specializing on discard utilization are able to flexibly respond to the temporary loss of discards by switching to alternative resources.

Intra-specific differences in foraging behaviour can have fitness consequences, especially during breeding. We combined GPS tracking data from 34 lesser black-backed gulls (Larus fuscus) encompassing 2029 foraging trips with dietary information and morphometric measurements to test the effect of breeding status and sex as well as body size on foraging behaviour. We found sexually distinct foraging strategies in this generalist seabird, which were maintained throughout the breeding season. The larger males travelled further from the colony than females, spent more time offshore, and remained longer at the nest during nest bouts. Males fed mostly on fisheries discards at offshore trawlers with few alternative resources nearby. Females foraged predominantly on land or nearshore and in the Wadden Sea, where they had multiple foraging options. Individuals differed in foraging behaviour along a continuum of predominantly terrestrial to predominantly marine foragers. Foraging range, trip duration, and the proportion of time at sea increased with wing length. Our findings did not support the usual inference that sexual segregation is mediated primarily by differences in competitive strength as both sexes foraged substantially in competitive settings around fishing vessels, but in different habitats. Females accessed a wider variety of resources and a broad prey spectrum, by exploring a whole suite of foraging opportunities and habitats nearer the colony. Different behavioural strategies (a combination of individual specialisation and sexual segregation) during breeding could reduce intra-specific resource competition, competition between the sexes (and hence within a pair), or alternatively, reduce the risk of unbalanced food provisioning

Recent developments and ubiquitous use of global positioning devices have revolutionised movement ecology. Scientists are able to collect increasingly larger movement datasets at increasingly smaller spatial and temporal resolutions. These data consist of trajectories in space and time, represented as time series of measured locations for each tagged animal. Such data are analysed and visualised using methods for estimation of home range or utilisation distribution, which are often based on 2D kernel density in geographic space. These methods have been developed for much sparser and smaller datasets obtained through very high frequency (VHF) radio telemetry. They focus on the spatial distribution of measurement locations and ignore time and sequentiality of measurements. We present an alternative geovisualisation method for spatio-temporal aggregation of trajectories of tagged animals: stacked space-time densities. The method was developed to visually portray temporal changes in animal use of space using a volumetric display in a space-time cube. We describe the algorithm for calculation of stacked densities using four different decay functions, normally used in space use studies: linear decay, bisquare decay, Gaussian decay and Brownian decay. We present a case study, where we visualise trajectories of lesser black backed gulls, collected over 30 days. We demonstrate how the method can be used to evaluate temporal site fidelity of each bird through identification of two different temporal movement patterns in the stacked density volume: spatio-temporal hot spots and spatial-only hot spots. Keywords: Animal movement; Space-time density; Space-time cube; Visual data exploration; Home range estimation; Utilisation distribution