Per- and poly-fluoroalkyl substances (hereafter PFAS) are widespread and persistent compounds that pose a threat to human and wildlife health. Wildlife monitoring is essential to understand the extent of PFAS contamination and its ecological drivers. Seabirds are good bioindicators of PFAS contamination of the marine environment, yet some areas, including the French coastlines, remain poorly covered. Here, we quantified 11 legacy PFAS in the plasma of 9 seabird species (n = 340 chicks) from 30 sites along the French Atlantic and Mediterranean coasts. Linear perfluorooctanesulfonic acid was by far the most abundant PFAS. Oceanic piscivorous species (Northern gannets Morus bassanus, black-legged kittiwakes Rissa tridactyla and Scopoli's shearwaters Calonectris diomedea) had the highest PFAS concentrations compared to Larus sp. gulls and shags Gulosus aristotelis. Overall, Mediterranean seabirds had lower perfluoroalkyl sulfonic acid and higher perfluoroalkyl carboxylic acid concentrations compared to Atlantic seabirds. At a finer spatial scale, chicks sampled near estuaries had a slightly higher PFAS burden, suggesting local riverine inputs. This first large-scale survey of PFAS in French seabirds reveals substantial heterogeneity in PFAS contamination across French coastal environments. Future work should address the sources of this PFAS contamination and quantify its toxicological consequences, given that sampled chicks may be at risk based on previous avian studies reporting PFAS-related health effects.

The recent large-scale circulation of High Pathogenicity Avian Influenza (HP AI) viruses H5Nx of clade 2.3.4.4b has been responsible for massive die-offs in wild species, notably in long-lived seabirds, with unknown implications for the immunity of surviving individuals. In the North Atlantic, northern gannet colonies were heavily affected in 2022, with more than 40% mortality observed among breeding adults and some surviving individuals developing dark irises. Using samples collected in 2023 and 2024 on Rouzic colony (France), we report persistent individual anti-AI antibody levels and seroneutralisation titres, with most of the immune individuals showing dark irises. A modelling approach further stressed the importance of long-lasting immunity in such species by showing that the proportion of individuals which kept their immunity between years strongly limited decreases in population size in case of repeated outbreaks. Overall, our results highlight the existence and importance of long-lasting immunity in long-lived species for population persistence.

Studying fine-scale movements of seabirds during migration is logistically challenging, but GPS technologies allow accurate tracking of individuals on their migratory journeys. Such data provide essential information in the context of offshore wind farm (OWF) developments, notably to anticipate spatial OWF overlap with migratory corridors and main foraging areas used along the routes of vulnerable species. Using high-precision GPS-GSM tags, we investigated the end of summer, southbound migration of two emblematic seabirds of French waters: Juvenile and adult Northern gannets Morus bassanus, and adult Balearic shearwaters Puffinus mauretanicus. Both species travel along the Southwestern European coast, between the Bay of Biscay and Western Africa, or the Mediterranean Sea. Adult gannets thereby migrate through the EEZ of up to 10 countries, six for juvenile gannet, and four for shearwaters. Combining behavioural segmentation based on hidden Markov models and utilization distribution modelling, we found that between two and 6 % of migration routes overlapped with proposed OWFs, with similar impacts on transit and foraging/resting areas. Studied seabirds were most at risk within Portuguese compared to Spanish waters, as they flew closest to OWFs (<10 km on average). While massive OWF developments are being planned within Western European coastal areas, our study suggests that offshore developments should be set >22 km away from the coast, to preserve transnational seabird migratory corridors.

Highly Pathogenic Avian Influenza Virus (HPAIV) is currently causing major wild animal population crashes all over the world including Antarctica. Yet, there are important knowledge gaps on the implications of long-lasting symptoms for the ecology of surviving individuals and the conservation of their populations. Using GPS tracking devices and long-term demographic data, we examined the effects of HPAIV on a seabird population of Northern gannets (Morus bassanus) in the colony of Rouzic, France. One year after the HPAIV outbreak of 2022, the breeding gannet population declined by 38 % and 22.3 % of surviving breeders were zombie birds: they had darkened irises, a black-eye symptom indicative of past infection to HPAIV. Importantly, we demonstrate that black eyes were not associated with detectable differences in the foraging behaviour and habitat use of surviving breeding gannets. Compared to years prior to the outbreak, the foraging effort of breeding individuals was lower and breeding success was higher, aligning with Ashmole's halo hypothesis, which posits that smaller seabird populations face lower intra-specific competition for food in the vicinity of their breeding colony and thereby, have a reduced foraging range. Our results highlight the importance of density-dependant mechanisms in population responses to sudden mass-mortalities, but raise conservation concerns, especially for species facing cumulative threats. In the long-term, locally depleted populations may reach critical thresholds where individual abundance and productivity may not be sufficient to maintain a positive demographic growth rate, ultimately leading to local population extinctions.

Seabirds are among the most threatened vertebrates, under pressure from fisheries bycatch, climate change, overfishing, and human disturbance. In France, demographic studies have highlighted adult survival as a key factor in population trends, which calls for large-scale marine conservation efforts. In this context, the Natura 2000 policy requires the designation of Special Protection Areas (SPAs) to protect seabirds under the Birds Directive. To assess the completeness of the French marine SPA network, data from aerial, boat, and coastal surveys, as well as tracking devices and distribution models, were collected for 57 seabird taxa. This data collection allowed the EU minimum criteria for a coherent SPA network to be spatially implemented, and the most ecologically valuable areas for seabirds around metropolitan France to be identified and prioritised, and overlaid with the current French SPA network and Marine Important Bird Areas (mIBAs) to identify potential inconsistencies. This analysis revealed seabird hotspots outside the existing ecological network, confirming some insufficiencies for coherent seabird conservation. Although data dependent, this analysis highlighted the limitations of using global proportion coverage to assess network coherence when coverage of biodiversity and abundance hotspots was not achieved. Furthermore, these results summarised the main target areas for policy makers to effectively improve seabird conservation around metropolitan France. In a context of increasing demands for marine spatial planning, improvements in this knowledge, the SPA network and conservation actions are required.

Animal movement paths display substantial complexity and variability, leading researchers to seek underlying rules that govern these patterns and mathematical models that best describe them. Using high-resolution (≥ 10 Hz) movement from 43 vertebrate species across diverse taxa, mass, and lifestyles, we show that movement paths are universally composed of straight-line steps interspersed with sharp turns, echoing a pattern documented for lower taxa such as bacteria. We report how these vertebrate ‘fundamental step lengths’ and ‘fundamental turn angles’, which are intrinsically different from the straight-line paths detailed in studies using low resolution position data, vary with species’ mass, lifestyle, behaviour, and environmental context. To explain these, we posit that animals inherently move in a straight line until sensory information signals a perceived better heading, which instigates a turn. The constellation of fundamental step lengths and turn angles over varying time intervals affects how well different models of animal movement (such as random walk or Lévy flight) fit lower resolution data. By examining turns as decision points, we can seek drivers of animal movement patterns and thereby work to predict future paths under varying conditions.

Density-dependent competition for food influences the foraging behaviour and demography of colonial animals, but how this influence varies across a species’ latitudinal range is poorly understood. Here we used satellite tracking from 21 Northern Gannet Morus bassanus colonies (39% of colonies worldwide, supporting 73% of the global population) during chick-rearing to test how foraging trip characteristics (distance and duration) covary with colony size (138–60 953 breeding pairs) and latitude across 89% of their latitudinal range (46.81–71.23° N). Tracking data for 1118 individuals showed that foraging trip duration and maximum distance both increased with square-root colony size. Foraging effort also varied between years for the same colony, consistent with a link to environmental variability. Trip duration and maximum distance also decreased with latitude, after controlling for colony size. Our results are consistent with density-dependent reduction in prey availability influencing colony size and reveal reduced competition at the poleward range margin. This provides a mechanism for rapid population growth at northern colonies and, therefore, a poleward shift in response to environmental change. Further work is required to understand when and how colonial animals deplete nearby prey, along with the positive and negative effects of social foraging behaviour.

La première observation confirmée de Mustela vison Schreber, 1777, le Vison d’Amérique, sur l’île Tomé (département des Côtes-d’Armor, Bretagne, France) date de 2012. Depuis, un programme d’action intitulé « Trégor Gestion Vison », réunissant les structures locales impliquées dans les problématiques environnementales, a été mis en place pour essayer d’éradiquer l’espèce sur cette île. Ce programme a permis de collecter, entre 2014 et 2020, du matériel biologique provenant de l’île Tomé (34 échantillons) mais également du continent proche (Côtes-d’Armor, 38 échantillons). Une étude génétique a été conduite, à partir de ce matériel biologique, afin d’identifier les modalités de la colonisation de l’île Tomé. À cet effet, l’ensemble des échantillons a été génotypé à 16 marqueurs microsatellites. Les résultats montrent que l’île Tomé n’est pas isolée du continent proche, dans la mesure où au moins cinq individus sont considérés comme des immigrants. Il est donc cohérent de penser qu’il y a en moyenne un individu qui colonise l’île chaque année. La mise en évidence de plusieurs événements de colonisation indique également que la colonisation de l’île se fait naturellement et qu’il ne peut s’agir d’une introduction délibérée. Ces résultats expliquent également pourquoi, après une éradication a priori réussie en 2018, l’île a de nouveau hébergé des visons à partir de 2020. Cette étude génétique apporte des résultats pouvant aider les gestionnaires dans la mise en place d’une stratégie de limitation des effectifs de visons présents sur l’île Tomé.

During 2021 and 2022 High Pathogenicity Avian Influenza (HPAI) killed thousands of wild birds across Europe and North America, suggesting a change in infection dynamics and a shift to new hosts, including seabirds. Northern Gannets Morus bassanus appeared to be especially severely impacted, but a detailed account of the data available is required to help understand how the HPAI virus (HPAIV) spread across the meta-population, and the ensuing demographic consequences. Accordingly, we analyse information on confirmed and suspected HPAIV outbreaks across most North Atlantic Gannet colonies and, for the largest colony (Bass Rock, UK), provide impacts on population size, breeding success, and preliminary results on apparent adult survival and serology. Unusually high numbers of dead Gannets were first noted at colonies in Iceland during April 2022. Outbreaks in May occurred in many Scottish colonies, followed by colonies in Canada, Germany and Norway. By the end of June, outbreaks had occurred in colonies in Canada and the English Channel. Outbreaks in 12 UK and Ireland colonies appeared to follow a clockwise pattern with the last infected colonies recorded in late August/September. Unusually high mortality was recorded at 40 colonies (75% of global total colonies). Dead birds testing positive for HPAIV H5N1 were associated with 58% of these colonies. At Bass Rock, the number of occupied nest-sites decreased by at least 71%, breeding success declined by c. 66% compared with the long-term UK mean and the resighting of marked individuals suggested that apparent adult survival between 2021 and 2022 could have been substantially lower than the preceding 10-year average. Serological investigation detected antibodies specific to H5 in apparently healthy birds, indicating that some Gannets recover from HPAIV infection. Further, most of these recovered birds had black irises, suggestive of a phenotypic indicator of previous infection. Untangling the impacts of HPAIV infection from other challenges faced by seabirds is key to establishing effective conservation strategies for threatened seabird populations as the likelihood of further epizootics increases, due to increasing habitat loss and the industrialization of poultry production.

Mercury (Hg) is a naturally occurring highly toxic element which circulation in ecosystems has been intensified by human activities. Hg is widely distributed, and marine environments act as its main final sink. Seabirds are relevant bioindicators of marine pollution and chicks are particularly suitable for biomonitoring pollutants as they reflect contamination at short spatiotemporal scales. This study aims to quantify blood Hg contamination and identify its drivers (trophic ecology inferred from stable isotopes of carbon (delta C-13) and nitrogen (delta N-15), geographical location, chick age and species) in chicks of eight seabird species from 32 French sites representing four marine subregions: the English Channel and the North Sea, the Celtic Sea, the Bay of Biscay and the Western Mediterranean. Hg concentrations in blood ranged from 0.04 mu g g(-1) dry weight (dw) in herring gulls to 6.15 mu g g(-1) dw in great black-backed gulls. Trophic position (delta N-15 values) was the main driver of interspecific differences, with species at higher trophic positions showing higher Hg concentrations. Feeding habitat (delta C-13 values) also contributed to variation in Hg contamination, with higher concentrations in generalist species relying on pelagic habitats. Conversely, colony location was a weak contributor, suggesting a relatively uniform Hg contamination along the French coastline. Most seabirds exhibited low Hg concentrations, with 74% of individuals categorized as no risk, and < 0.5% at moderate risk, according to toxicity thresholds. However, recent work has shown physiological and fitness impairments in seabirds bearing Hg burdens considered to be safe, calling for precautional use of toxicity thresholds, and for studies that evaluate the impact of Hg on chick development.

High pathogenicity avian influenza virus (HPAIV) caused the worst seabird mass-mortalities on record in Europe across 2021-2022. The northern gannet ( Morus bassanus ) was one of the most affected species, with tens of thousands of casualties in the northeast Atlantic between April-September 2022. Disease outbreaks can drastically modify the movement ecology of animals and diminish spatial consistency, thereby increasing the potential for disease transmission. To detect potential changes in movement behaviour, we GPS-tracked breeding adults following the initial HPAIV outbreak, at three of the largest gannet breeding colonies where major mortality of adults and chicks occurred (Bass Rock, Scotland, UK; Grassholm, Wales, UK; Rouzic island, Brittany, France). Crucially, GPS-tracked birds remained faithful to their breeding sites and did not prospect other breeding colonies. They performed regular foraging trips at sea, similar to their behaviour before the outbreak. Gannet foraging effort was nonetheless lower than in 2019, thus surviving birds may have benefited from reduced intra- and interspecific food competition. Breeding colony fidelity of adult northern gannets following HPAIV mass-mortalities suggests limited long-term capacity to virus spread, which may contrast with the behaviour of adults during the disease outbreak, or with that of younger individuals.

Storms can cause widespread seabird stranding and wrecking,1,2,3,4,5 yet little is known about the maximum wind speeds that birds are able to tolerate or the conditions they avoid. We analyzed >300,000 h of tracking data from 18 seabird species, including flapping and soaring fliers, to assess how flight morphology affects wind selectivity, both at fine scales (hourly movement steps) and across the breeding season. We found no general preference or avoidance of particular wind speeds within foraging tracks. This suggests seabird flight morphology is adapted to a “wind niche,” with higher wing loading being selected in windier environments. In support of this, wing loading was positively related to the median wind speeds on the breeding grounds, as well as the maximum wind speeds in which birds flew. Yet globally, the highest wind speeds occur in the tropics (in association with tropical cyclones) where birds are morphologically adapted to low median wind speeds. Tropical species must therefore show behavioral responses to extreme winds, including long-range avoidance of wind speeds that can be twice their operable maxima. By contrast, Procellariiformes flew in almost all wind speeds they encountered at a seasonal scale. Despite this, we describe a small number of cases where albatrosses avoided strong winds at close range, including by flying into the eye of the storm. Extreme winds appear to pose context-dependent risks to seabirds, and more information is needed on the factors that determine the hierarchy of risk, given the impact of global change on storm intensity.6,7

Seabirds are one of the most threatened of all bird groups, with a marked community-wide decline across the last decades. Yet, some seabird species are more resilient than others, and it is essential to study under which conditions even these highly resilient organisms are affected by global changes. Here, we report such a case in northern gannets (Morus bassanus). Using global location sensors (GLS), demographic and stable isotope analyses, we performed a long-term study of the migration biology and inter-annual survival of gannets breeding on Rouzic Island in Brittany, France. Across 2006–2015, our analyses showed that the birds spent the inter-breeding period off Western Europe, in the Mediterranean or off West Africa. There were no inter-annual trends in the use of these different areas, but isotopic analyses suggested food competition between gannets and industrial-scale fisheries. Crucially, we found a precipitous decline in the return rates of birds equipped with GLS, from 100% in 2006–2007 to less than 30% after 2015. This decline was consistent with a marked decrease in inter-annual survival probabilities for ringed adult gannets, from > 90% in 2014–2015 to < 60% in 2018–2019, and with a population decline of the Rouzic gannet breeding colony in recent years. Strong ecological signals provided by northern gannets point to critical marine ecosystem perturbation in the Eastern Atlantic, and the decline of this resilient and emblematic species should lead to the urgently needed transformation of marine policies.

Fisheries modify ecosystem balance by harvesting through marine food webs and producing large amounts of discards subsidizing scavengers. Among them, seabirds are the most conspicuous and have been benefiting from anthropogenic food sources generated by fisheries. However, this modified feeding behaviour also exposes them to threats, such as accidental bycatch on fishing gear and ecological traps set by discards of lower nutritional value compared to seabird natural prey. Seabird-fishery interactions have been the focus of numerous studies, but very few integrative investigations tested multi-annual dynamics. To explore this temporal dimension, we performed stable isotopic and body condition analyses, as well as GPS-tracking in Northern gannets (Morus bassanus) over a 12-year period (2005–2017), during which they coexisted with fisheries in the English Channel. We demonstrate that gannets fed either on natural prey, or fishery wastes, but that discard consumption induced increased seabird foraging effort and reduced adult body condition. These changes are concomitant with reduced gannet reproductive success, and reduced growth rate of their breeding population. Our work provides essential, novel understanding of scavengers-fisheries interactions, by showing that fishery discards do not compensate natural prey shortage in the longer term. Altered gannet foraging and fitness strongly suggest pelagic fish depletion threatening Northern gannets in the English Channel. To improve gannet conservation in this ecoregion, fishery discards may be banned, but, efforts should in priority go towards rebuilding Northern gannet pelagic prey populations, particularly by strongly reducing fishing effort on North Atlantic mackerel.

Grey (Halichoerus grypus) and harbour seals (Phoca vitulina) are sympatric seal species, but they display distinct strategies of habitat use and connectivity between haulout sites. The distribution patterns and variations in relative abundance of both species were investigated along the French coast of the English Channel, at the southern limit of their range where seal numbers are increasing. Regular censuses conducted at all main haulout sites in mainland France showed significant seasonal variations at most sites, with more harbour seals counted during summer (breeding and moulting seasons), and more grey seals during summer only in the eastern English Channel. Trends in maximum haulout numbers at haulout sites showed a significant increase over the last five years, ranging from 9.7% to 30.9% per year for harbour seals, and from 5.8% (in the western English Channel) to 49.2% (in the eastern English Channel) per year for grey seals. These rates of increase in grey seal numbers are not linked to local pup production and most probably result from seal movements from the southwest British Isles and the North Sea, respectively. Aerial surveys conducted across the English Channel showed that most seal observations at sea were concentrated in the north-eastern English Channel. Telemetry showed that the 28 harbour seals tracked remained highly coastal, within a radius of 100km from their haulout sites, and did not move to other known colonies. Grey seals moved much greater distances, reaching up to 1200km from their capture site. More than half of the 45 grey seals tracked crossed the English Channel, especially during the breeding season, moving to known colonies in the southwest British Isles and the North Sea. Combining individual tracks and long-term surveys of the seal populations allowed a better understanding of the dynamics of these populations and their connectivity at a larger regional scale. The findings provide direct information for the management of grey and harbour seals within the frame of the Marine Strategy Framework Directive, and highlight focus areas where potential interactions between the two species should be monitored.

Seeing the ocean through the eyes of seabirds could help meet the challenges of managing common-pool marine resources both in protected and unprotected areas. First, seabirds are top-predators, exposed to all threats affecting the oceans, and this makes them ideal sentinel organisms for monitoring changes within marine ecosystems. Second, seabirds cross both ecological and political boundaries, and following their movements should help making interdependencies within and between marine ecosystems more visible. Third, seabirds are conspicuous and often charismatic animals, which interact differently with different groups of stakeholders and provide the opportunity to acknowledge and discuss each other's values and interests. In this paper, we present these research avenues using a seabirds’ view, for tackling marine conservation and management issues, and we give operational examples of implementation based on our work in the English Channel.

When animals move across a landscape, they alternate between active searching phases in areas with high prey density and commuting phases towards and in-between profitable feeding patches. Such active searching movements are more sinuous than travelling movements, and supposedly more costly in energy. Here we provide an empirical validation of this long-lasting assumption. To this end, we evaluated simultaneously energy expenditure and trajectory in northern gannets (Morus bassanus) using GPS loggers, dive recorders and three-dimensional accelerometers. Three behavioural states were determined from GPS data: foraging, when birds actively searched for prey (high tortuosity, medium speed); travelling, when birds were commuting (straight trajectory, high speed); and resting (straight trajectory, low speed). Overall dynamic body acceleration, calculated from acceleration data, was used as a proxy for energy expenditure during flight. The impact of windscape characteristics (wind force and direction) upon flight costs was also tested. Energy expenditure of northern gannets was higher during sinuous foraging flight than during more rectilinear travelling flight, demonstrating that turns are indeed costly. Yet wind force and direction also strongly shaped flight energy expenditure; within any behavioural state it was less costly to fly with the wind than against it, and less costly to fly with strong winds. Despite the major flight costs of wind action, birds did not fully optimize their flight track relative to wind direction, probably because of prey distributions relative to the coastline and wind predictability. Our study illustrates how both tortuosity and windscape shape the foraging costs of marine predators such as northern gannets.

Foreign fisheries massively harvest waters off West Africa, plundering local marine economies and threatening African food security. Here we warn that these fisheries might affect both juvenile and adult European seabirds during their autumn migration and at their wintering grounds. Using miniaturised GPS, satellite transmitters and geolocators, we tracked the migratory movements of 64 adult and juvenile Northern gannets (Morus bassanus) and Scopoli's shearwaters (Calonectris diomedea) after their breeding season in the eastern Atlantic and the Mediterranean Sea, respectively. It was the first time ever that the movements of gannet fledglings were tracked with GPS accuracy. During winter (October to March) birds made extensive use of marine areas within the exclusive economic zones of Morocco, Western Sahara, Mauritania and Senegal. These juvenile and adult European seabirds are therefore dependent upon African marine resources and at risk from competition with fisheries, as well as intentional and incidental mortality by fishing gear. Those threats occur additionally to detrimental seabird fishery interactions in Europe. There is an urgent need for improved marine conservation off West Africa, and our data demonstrating connectivity between specific European breeding colonies and African wintering areas are a major step towards stakeholder involvement. (C) 2014 Elsevier Ltd. All rights reserved.