Larus Michahellis Research Articles

Antimicrobial Resistance and Pathotypes of Escherichia coli Isolates from Yellow-Legged Seagulls (Larus michahellis) in Central Italy

Seagulls are synanthropic wild birds that can contaminate, through their droppings, beaches, urban and peri-urban environments. This concern is more serious when seagulls eliminate antimicrobial-resistant pathogenic bacteria. This study analyzed the fecal samples from 137 yellow-legged seagulls (Larus michahellis) from Central Italy. A total of 218 Escherichia coli strains were isolated and analyzed for phenotypic and genotypic antimicrobial resistance and to identify the virulence genes characterizing different pathotypes. The disk diffusion method on all isolates found relevant resistance rates to ampicillin (38.99%), tetracycline (23.85%), and enrofloxacin (21.10%). On the basis of all results obtained with this test, 62 (28.44%) isolates were classified as multidrug-resistant (MDR) and 6 (2.75%) as extensive drug-resistant (XDR). Molecular analyses conducted on the strains phenotypically resistant to carbapenems, cephalosporins, and penicillins found 9/37 (24.32%) strains positive for blaOXA-48, 52/103 (50.49%) for blaTEM, 12/103 (11.65%) for blaCMY2, 3/103 (2.91%) for blaCTX, and 1/103 (0.97%,) for blaSHV. PCR to detect virulence genes characterizing different pathotypes found that 40 (18.35%) isolates had the astA gene, indicative of the enteroaggregative (EAEC) pathotype, 2 (0.92%) had cnf1, 2 (0.92%) had cnf2, and 1 (0.46%) had cdt-IV. All five (2.29%) strains were reportable as necrotoxigenic (NTEC), while 4 (1.83%) had both eaeA and escV, reportable as enteropathogenic (EPEC). Measures to limit seagulls’ access where humans and other animals reside are pivotal to reduce the risk of infection with antimicrobial-resistant and pathogenetic E. coli strains.

Plastic ingestion in aquatic insects: Implications of waterbirds and landfills and association with stable isotopes

Wetlands provide numerous ecosystem services including freshwater purification. Nonetheless, their functionality is continuously impacted by many pollutants. Plastics are considered as an emerging threat for these ecosystems, but only recently have studies began to focus on plastic and microplastic (MP) contamination in wetlands, especially in biota. This study aims to investigate the abundance of MPs in two ubiquitous aquatic insect taxa (i.e. Corixidae (Hemiptera) and Chironomidae (Diptera)) collected in twelve zones within Mediterranean wetlands belonging to three basins located in Andalusia (south-west Spain). We compared MP contamination across basins and tested the proximity to landfills and presence of colonial waterbirds [i.e. white storks (Ciconia ciconia) and gulls (Larus michahellis and L. fuscus)] on MP abundance in aquatic insects. We also performed stable isotope analyses of nitrogen and carbon (δ15N and δ13C) to evaluate the potential association between MP abundance and isotopic values. We detected 571 suspected MPs (mostly blue fibers) in insects of different developmental stages (i.e., larvae, pupae, nymphs and adults). Polyesters and polypropylene were the most frequent polymers detected. The generalized linear mixed models indicated that MP abundance decreased with increasing distance from landfills; but it also increased in sites with birds that fed on landfills and roost in wetlands. When controlling for landfill effects, sites in the smallest basin (Guadalete) had lower MP contamination than those in Odiel-Tinto and the much larger (>15×) Guadalquivir. Moreover, we found a negative association between MPs items/g (or mean MPs) and 15N isotopes in adult corixids. Our findings showed that MP pollution is present in all the study areas, including strictly protected wetlands. The use of aquatic insects for biomonitoring of MP pollution can help identify priority areas for management actions to mitigate plastic pollution.

Exploring the use of gull eggs as bioindicators of phthalate esters exposure

Plastic pollution and associated plasticizers are a global threat affecting aquatic environments. Phthalates are among the most used plasticizers that can impact on fauna due to their endocrine-disrupting properties. The aim of this study was to investigate the use of eggs of Audouin’s gull (Larus audouinii) and yellow-legged gull (Larus michahellis) as biomonitors of phthalate exposure. Sixteen phthalates were studied and the extraction and purification steps were optimized using various sorbents and clean-up processes to efficiently recover these contaminants in gull eggs. Analysis was performed using ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) using multiple reaction monitoring to obtain high selectivity and sensitivity. Quality control parameters and a comprehensive analysis of blank contribution are provided. The best performance was obtained with Oasis PRiME HLB cartridges with recoveries from 61 to 138% for most of the compounds. Pooled gull-egg samples from seven breeding colonies collected over the period 2016 – 2021 within the Iberian Peninsula revealed the presence of dibutoxyethyl phthalate (DBEP), hexyl 2-ethylhexyl phthalate (HEHP), dimethyl phthalate (DMP), diethyl phthalate (DEP), and dibutyl phthalate (DBP) at mean concentrations ranging from 2.27 to 1330 ng/g ww in Audouin's gull and from 2.74 to 487 ng/g ww in yellow-legged gull (DBP not detected). The absence of other phthalates is likely attributable to their metabolism and excretion by female adults. Overall, this study provides an accurate method to analyse phthalates in gull eggs and supports their use as bioindicators of phthalate contamination.

Evil and allies: Opportunistic gulls as both spreaders and sentinels of antibiotic‐resistant bacteria in human‐transformed landscapes

Abstract Human‐transformed residuals, especially those derived from human waste (dumps), farmland, and livestock are involved in the emergence of antibiotic‐resistant bacteria (ARB) in the environment. Wildlife can act as vectors of ARB dispersal through different environments, but also as sentinels to detect the early spread and determine ARB sources. The development of integrated monitoring programmes focused on wildlife would help to anticipate the risks of ARB to humans and livestock. We used the yellow‐legged gull (Larus michahellis) as a model species to investigate and monitor the spatial patterns of ARB dispersal across an extensive farmland region located in northeastern Spain (Lleida). By integrating GPS tracking data and ARB clinical testing for 26 individuals within a network analysis framework, we modelled the risk of spatial pathogen spread through faeces during the bacteria‐transmission latency period (16 days after sample collection). Additionally, we created a connectivity network to determine the main sources of ARB in the area, focusing on three main habitats of special risk for infection: dumps, livestock facilities, and irrigation ponds. Seven individuals were infected by Escherichia coli, with one also co‐infected with Listeria monocytogenes and Salmonella spp. Potential pathogen dispersal distances ranged from 1.13 km to 23.13 km from the breeding colony. Our network analyses revealed 54 main nodes (i.e. high‐risk habitats recurrently visited by tracked gulls) and 1182 links among them. Our findings revealed a high degree of connectivity between the breeding area, located in a shallow lake, and nearby dumps, highlighting them as significant contributors to ARB dispersal. Synthesis and applications: The integration of GPS data, pathogen testing and network analyses can shed further light on pathogen dynamics by creating spatial risk maps and identifying ARB sources. In combination with complementary molecular epidemiology techniques within a One Health framework, our approach can emerge as an important tool for monitoring ARB dynamics within highly human‐transformed ecosystems. This may empower managers for the development of targeted ARB monitoring programmes and effective mitigation strategies, ultimately improving both animal and public health.

Age-related presence and genetic diversity of Campylobacter spp. in young and adult yellow-legged gulls (Larus michahellis) in Croatia.

The epidemiology of Campylobacter species in wild birds is still poorly understood. This study describes the occurrence and genetic diversity of Campylobacter in adult and nestlings of yellow-legged gulls, highlighting differences between breeding locations. The gulls were captured in Croatia between 2021 and 2023. A cloacal swab was taken from each individual and tested for the presence of Campylobacter. Isolated Campylobacter species were genotyped using the multilocus sequence typing (MLST) method. A total of 1071 gulls were captured and sampled, of which 152 samples were identified as Campylobacter species, with Campylobacter jejuni (9.90%) being the most frequently isolated bacterium, followed by Campylobacter lari (3.36%) and Campylobacter coli (0.93%). Complete sequence type (ST) profiles were generated for 141 isolates: 100 C. jejuni, 33 C. lari, and 8 C. coli. A significant difference in the occurrence of positive Campylobacter species was found depending on the sampling sites, while both sampling site and age were significant for the occurrence of C. jejuni. Adults and nestlings showed high genetic diversity for C. jejuni and C. lari, and there were no significant differences between strains isolated from adults and nestlings or between sites, suggesting a high genotype flow in the studied gull population.

Spatial variation of mercury contamination in yellow-legged gulls (Larus michahellis) in the Western Mediterranean

Mercury (Hg) is a global pollutant of major concern in marine and coastal environments. In the Mediterranean Sea, Hg concentrations in biota are higher than in other seas, even when seawater concentrations are similar. Seabirds, as marine top predators, can reflect Hg contamination on a large spatial scale. By sampling seabirds at 17 different breeding colonies, we evaluated Hg concentrations of yellow-legged gulls (Larus michahellis) in the occidental Mediterranean basin in 2021 and 2022. More specifically, we investigated spatial variation of Hg contamination in both chicks and adults as well as associated toxicological risks through the use of blood and feathers, which reflect contamination over different periods of the year. The highest concentrations in chicks were found in Djerba (Tunisia) with blood Hg values of (mean ± SD) 1.69 ± 0.51 μg g−1 dry weight (dw). Adults were most contaminated in Djerba and Dragonera (Balearic Islands, Spain) with blood Hg concentrations of respectively 3.78 ± 2.54 and 5.25 ± 3.73 μg g−1 dw. Trophic ecology was investigated using stable isotope analyses (δ13C, δ15N and δ34S as proxies of feeding habitat and diet), and showed that spatial variation in Hg was mainly driven by foraging habitat in both chicks and adults. Low Hg concentrations were related to the use of anthropogenic food sources. An effect of colony location was also found, suggesting spatial differences in local environmental pollution transfer up to seabirds. Our results also supported the use of δ34S to discriminate between marine and continental foraging habitats in generalist seabirds. This study provides new insights onto the spatial distribution of Hg contamination in a widespread seabird, reporting some of the highest Hg values recorded for this species. Populations with highest concentrations are of potential concern regarding toxicological risks.

Anthropogenic debris pollution in yellow-legged gull (Larus michahellis atlantis) nests in biosphere reserves of the Canary Islands

Anthropogenic debris, particularly plastic pollution, has emerged as a significant environmental threat to biodiversity. Given that seabirds interact with artificial debris through ingestion, entanglement, and nest incorporation, it is particularly important to quantify the quantity, origins, and chemical composition of these debris items. In this work, it was evaluated for the first time the occurrence of anthropogenic debris in nests of yellow-legged gull (Larus michahellis atlantis) in biosphere reserves of the Canary Islands (Spain). A total of 48 abandoned nests were collected from five remote and hardly accessible sampling areas, revealing that 81.3 % contained anthropogenic waste, with plastic accounting for 34.7 % of the debris, followed by metal (33.6 %) and paper (19.6 %). On average, 32.8 ± 40.9 items were found per nest. Regarding the origin, food packagings (47.8 %), personal hygiene products (21.7 %), and textiles (15.8 %) were identified as the predominant sources. Furthermore, the polymer composition of the plastics was characterised by means of Fourier-transform infrared spectroscopy analysis, being polyester the most abundant (38.2 %), followed by polyethylene (25.6 %) and rayon (10.3 %). The incorporation of anthropogenic debris into nest construction may result from outdoor human activities carried out far from nesting areas.

Physiology and fertility of two gull species in relation to plastic additives' exposure

Understanding the impact of plastic and its additives on wild species is crucial as their presence in the environment increases. Polybrominated diphenyl ethers (PBDEs), once used as flame retardants, were restricted due to known toxic effects, but are still detected in the environment. Naturally occurring methoxylated PBDEs (MeO-BDEs) can result from PBDE transformation and may cause similar hazardous effects. Yellow-legged gulls (Larus michahellis, YLG) and Audouin's gulls (Ichthyaetus audouinii, AG) are highly susceptible to plastic additives, due to their distribution, trophic position, and behaviour. In this study, we assessed PBDEs and MeO-BDEs uptake in different tissues and their effects on physiological and reproductive parameters. Findings indicate that, apart from annual differences, adult AG accumulated more MeO-BDEs than YLG in a natural breeding habitat (Deserta), while the latter had lower PBDE levels than YLG breeding in the city of Porto. In relation to chicks, only YLG from Deserta showed higher PBDE concentrations than AG chicks. Individual analysis of each physiological parameter revealed impacts only for adult YLG from Deserta, with neurofunction and immune system inhibition at higher MeO-BDE concentrations. For chicks, AG showed impaired neurofunction, while YLG chicks from Porto exhibited potential genotoxicity effects triggered by higher MeO-BDE levels. Overall health analysis showed activation of antioxidant defences and compromised immune system in YLG adults from Porto due to high values of PBDEs, while chicks from Deserta exhibited inflammation and oxidative stress with high concentrations of MeO-BDEs in the same species. Fertility parameters showed significant differences for sperm counts though suggesting individuals may be able to compensate any exposure effects. This study confirms the widespread presence of plastic-associated compounds and their harmful effects on gulls, particularly on neurofunction, immune system, oxidative balance and fertility, especially due to the presence of MeO-BDEs.

Assessing the impacts of trace element contamination on the physiology and health of seabirds breeding along the western and southern coasts of Portugal

Coastal seabirds serve as sentinels of ecosystem health due to their vulnerability to contamination from human activities. However, our understanding on how contaminant burdens affect the physiological and health condition of seabirds is still scarce, raising the uncertainty on the species' vulnerability vs tolerance to environmental contamination. Here, we quantified 15 Trace Elements (TE) in the blood of gull (yellow-legged gull Larus michahellis and Audouin's gull Ichthyaetus audouinii) and shearwater (Cory's shearwater Calonectris borealis) adults, breeding in five colonies along the Portuguese coastline. Additionally, stable isotopes of carbon (δ13C) and nitrogen (δ15N) were quantified to elucidate foraging habitat and trophic ecology of adults, to identify potential patterns of TE contamination among colonies. We used immuno-haematological parameters as response variables to assess the influence of TE concentrations, stable isotope values, and breeding colony on adults' physiological and health condition. Remarkably, we found blood mercury (Hg) and lead (Pb) concentrations to exceed reported toxicity thresholds in 25% and 13% of individuals, respectively, raising ecotoxicological concerns for these populations. The breeding colony was the primary factor explaining variation in five out of six models, underlining the influence of inherent species needs on immuno-haematological parameters. Model selection indicated a negative relationship between erythrocyte sedimentation rate and both Hg and selenium (Se) concentrations, but a positive relationship with δ13C. The number of immature erythrocyte counts was positively related to Hg and Se, particularly in yellow-legged gulls from one colony, highlighting the colony-site context's influence on haematological parameters. Further research is needed to determine whether essential TE concentrations, particularly copper (Cu) and Se, are falling outside the normal range for seabirds or meet species-specific requirements. Continuous monitoring of non-essential TE concentrations like aluminium (Al), Hg, and Pb, is crucial due to their potential hazardous concentrations, as observed in our study colonies.

Unravelling urban nesting site selection in an opportunistic gull: an integrated analysis of micro-spatial habitat and litter quantification

The proliferation of gull populations in urban areas has led to an increase in human-gull conflicts, especially in highly populated cities where these opportunistic predators are often considered a nuisance. There is a lack of data regarding the selection of nesting sites by gulls, so management measures at nesting level cannot be implemented. Here, we investigated the main environmental factors that explain the nesting preferences of the yellow-legged gull (Larus michahellis) in urban areas, using the population in the city of Barcelona (NE Spain) as study model. We conducted an integrated analysis that combines micro-scale habitat selection assessments of 148 urban nesting sites with a macro-scale assessment of gull movements derived from GPS tracking of breeding yellow-legged gulls. We also analysed the type and abundance of litter in nests and main factors related to this. Nests were mainly found on flat roofs or above a structure on the main roof located at corner placements and situated on gravel substrate. Nest selection showed a negative relation to port distance and a building height beyond 12 m. The presence of litter was detected in more than 80% nests and was related to population density. Understanding the ecology of yellow-legged gulls in urban areas has implications for urban population management to prevent nest establishment.

First evidence of microplastics and their characterization in yellow-legged gull (Larus michahellis michahellis, Naumann, 1840) pellets collected from the Sfax salina, southeastern Tunisia

The aim of this work was to provide evidence on the presence of microplastics (MPs) in regurgitated Yellow-legged Gull pellets (n = 18) from Sfax salina (south-eastern Tunisia). This artificial area is subject to high anthropogenic pressure and hosts Yellow-legged Gulls, which are at the top of the trophic chain and can be used as sentinel species to monitor litter in the environment, including plastic pollution. The total number of MPs found in the samples was 309, 63.8 % fibres (4.95 ± 3.51 MPs/g) and 36.2 % fragments (2.87 ± 1.74 MPs/g). Micro-FTIR analysis evidenced that a large proportion of the fibres was attributed to artificial cellulose (40.7 %). Ethylene vinyl acetate (EVA) and polyethylene (PE) were found in the fragments.

Biogeography and ecology of the Algerian island flora

Background and aims – In spite of their proximity to the coasts, the flora of the islands and islets of the Algerian coasts has been poorly studied. This work is the first to provide an overall view of the richness and the determinants of the Algerian island flora. Material and methods – The study is based on a compilation of original floristic data. Two classifications of 30 islands and islets were derived from PCA and HCPC performed on the species occurrence matrix and on a matrix of flora descriptors including species richness, functional traits (life form, seed dispersal, pollination), and biogeographic range. We performed an RDA to explain the variation in flora characteristics by a set of physiographic (longitude, latitude, elevation, area, isolation, steepness index, and area/perimeter ratio) and biotic (seabird density and human presence) variables. Key results – The floristic inventory encompassed a total richness of 295 vascular plant taxa (including subspecies and varieties) on the 30 studied sites. Five main groups of islands and islets can be distinguished based on vegetation composition and three from flora descriptors. RDA model selection revealed that the combination of four variables (seabird density, area, latitude, and longitude) explained 26.6% of the variation in flora characteristics. Taken alone, the density of yellow-legged gull colonies and the island area were the main drivers of this variation. Results showed that floristic richness was associated with larger island area and higher seabird density, the importance of some plant functional traits, such as zoochory and entomogamy, and with a higher proportion of Eurasian holarctic species. Conclusion – In the context of island flora conservation, some of these small islands of Algeria can be considered as “modern refuges” from human pressures, and this is particularly important in the context of Mediterranean ecosystems characterised by a quasi-permanent human impact in various habitats. Two new important plant areas (IPAs) for Algeria are proposed following the results of these floristic inventories.

Long-term monitoring of dwarf eggs in clutches of Yellow-legged Gulls (Larus michahellis) breeding in a western Mediterranean colony

The present study provides data on clutches with dwarf eggs from a large sampling in a colony of Yellow-legged Gulls (Larus michahellis) over 31 years. Their occurrence was very low, with a global percentage of 0.26%. Significant variations were not detected among periods of 10 or 11 years. In all the cases, only one dwarf egg was found per clutch. Mean volume of dwarf eggs was 34% of that of non-dwarf eggs. Their content was mostly albumen and a very reduced quantity of yolk, and they were infertile. Several results of the study (the laying order of the dwarf eggs, their mean clutch size and the mean size of the non-dwarf eggs from clutches with dwarf eggs) support the hypotheses that runt eggs occur from a temporary disturbance to the reproductive tract.

Rapid loss of maternal immunity and increase in environmentally mediated antibody generation in urban gulls

Monitoring pathogen circulation in wildlife sentinel populations can help to understand and predict the spread of disease at the wildlife-livestock-human interface. Immobile young provide a useful target population for disease surveillance, since they can be easily captured for sampling and their levels of antibodies against infectious agents can provide an index of localized circulation. However, early-life immune responses include both maternally-derived antibodies and antibodies resulting from exposure to pathogens, and disentangling these two processes requires understanding their individual dynamics. We conducted an egg-swapping experiment in an urban-nesting sentinel seabird, the yellow-legged gull, and measured antibody levels against three pathogens of interest (avian influenza virus AIV, Toxoplasma gondii TOX, and infectious bronchitis virus IBV) across various life stages, throughout chick growth, and between nestlings raised by biological or non-biological parents. We found that levels of background circulation differed among pathogens, with AIV antibodies widely present across all life stages, TOX antibodies rarer, and IBV antibodies absent. Antibody titers declined steadily from adult through egg, nestling, and chick stages. For the two circulating pathogens, maternal antibodies declined exponentially after hatching at similar rates, but the rate of linear increase due to environmental exposure was significantly higher in the more prevalent pathogen (AIV). Differences in nestling antibody levels due to parental effects also persisted longer for AIV (25 days, vs. 14 days for TOX). Our results suggest that yellow-legged gulls can be a useful sentinel population of locally transmitted infectious agents, provided that chicks are sampled at ages when environmental exposure outweighs maternal effects.

Potential effects of avian predators on the behaviour of the Little Bustard Tetrax tetrax during the display season in a cereal pseudo-steppe

The Little Bustard Tetrax tetrax is an endangered steppe bird whose last remaining breeding populations in Catalonia (NW Spain) are located in the Lleida plains. Although the decline in this population is mainly associated with habitat loss and degradation due to agricultural intensification and urban encroachment, the proliferation of predators, some favoured by hu- mans, may also be having negative effects on this population, either through direct predation or indirect effects on behaviour and survival. Here, we describe the type of behavioural response exhibited by Little Bustards during the display season when they encounter a potential avian predator and discuss the possible indirect effects of these interactions. During counts carried out in the springs of 2010–2022 in three Special Protection Areas in the Lleida plains, 88 encounters between Little Bustards and eight species of avian predators were recorded. Among them, the Western Marsh Harrier Circus aeruginosus, Montagu’s Harrier C. pygargus and the Yellow-legged Gull Larus michahellis were the most frequent species involved in these encounters, although only the Yellow-legged Gull conducted deliberate attacks in a consistent way. Irrespective of the predator or its attitude, most encounters resulted in the Little Bustard being flushed. The number of encounters were higher at the beginning of the mating season, which may prevent Little Bustards from settling in otherwise suitable areas of habitat. The flushing of the bustards may increase the risk of collision with power lines and reduce mating success. Since the number of encounters between Yellow-legged Gulls and Little Bustards seems to have increased in recent years in the study area, we believe that there is a need to conduct further studies to understand how these interactions affect the population dynamics and conservation of this endangered species.

To the fauna of rare bird species of coastal habitats of Temryuk Bay

New information on the presence of 27 rare, protected or little-studied species and subspecies of birds (greylag and red-breasted geese, common shelduck, gadwall, common pochard, Eurasian oystercatcher, pied avocet, black-winged stilt, Eurasian golden-plover, Eurasian curlew, sanderling, common greenshank, yellow-legged, great black-headed, Mediterranean, slender-billed, and little gulls, Caspian tern, European turtle-dove, great white and dalmatian pelicans, squacco heron, glossy ibis, Eurasian spoonbill, lesser spotted and white-tailed eagles, Eurasian hobby) obtained in the Temryuk region (Eastern Azov region) in different seasons of 2022-2023. The coast of the bay is a stopping place on the spring migration of Eurasian oystercatcher, pied avocet, Eurasian golden-plover, Eurasian curlew, sanderling, common greenshank, common shelduck, slender-billed gull, and Caspian tern; in the fall - pied avocet, sanderling, and Caspian tern. Information about the migration of the sanderling at the end of March has been obtained for the first time. The location of the concentration of Caspian tern and slender-billed gull has been identified. The glossy ibis, the number of which is growing, the black-winged stilt, and the great black-headed gull remain in the spring-summer period in the flooded rice fields. Harvested rice fields provide valuable habitat for Eurasian spoonbills during their fall migration. Information about a large aggregation of red-breasted goose in rice fields in January 2023 is presented for the first time. The great black-headed gull is found on estuaries in all seasons. The common pochard, gadwall, little gull, and Dalmatian pelican stop at the estuaries during the migration period. The migration of the lesser spotted eagle at the end of September and the migration of a large flock of great white pelican in May were recorded in this area for the first time. The squacco heron, which is disturbance tolerant, is common in reed habitats of estuaries and irrigation canals.

Habitat use of urban nesting yellow-legged gulls in Croatia during the breeding season

Because of increasing urbanization, some opportunistic birds such as gulls, started to exploit various artificial marine and terrestrial food sources. To better understand urban gull ecology and habitat use, a study was done on a yellow-legged gull (Larus michahellis) during the breeding season in Zadar, a coastal city on the Adriatic Sea. Ten adult breeding yellow-legged gulls (five females and five males) were caught on building rooftops during the late incubation period and were fitted with GPS-GSM solar power transmitters. In total, 2377 trip segments (no. GPS points = 19906) were analyzed, with most of them being classified as nest attendance (56.32 %) and foraging movements (37.10 %). Tracking data showed that the gulls mostly use marine and urban areas, agricultural lands, a dump site, and grasslands. Females were more active while foraging, with a longer duration and trip segment length, travelling further away from the breeding colony, while males tended to rest more than females. Both males and females exploit various habitats for foraging and resting, however females used agricultural lands significantly more than males. Even though gulls are generalists, some individuals showed a preference for certain habitats. After calculating the proportional similarity index, individuals showed high specialization for a certain habitat.

Sources of persistent organic pollutants and their physiological effects on opportunistic urban gulls

Urbanization is associated with drastic shifts in biodiversity. While some species thrive in urban areas, the impact of inhabiting these human-altered environments on organism physiology remains understudied. We investigated how exposure to polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) affects the physiology of yellow-legged gulls (Larus michahellis) inhabiting a densely populated, industrialized city. We analyzed blood samples from 50 gulls (20 immatures and 30 adults) and assessed 27 physiological parameters and biomarkers related to xenobiotic protection, health, and feeding habits in these same individuals. We also tracked the movements of 25 gulls (15 immatures and 10 adults) to identify potential sources of persistent organic pollutants (POPs). Both adult and immature gulls primarily inhabited urban areas, followed by marine habitats. Immature gulls spent more time in freshwater, landfills, and agricultural areas. Bioaccumulated ΣPCB (median = 92.7 ng g-1 ww, 1.86–592) and ΣPBDE (median = 1.44 ng g-1 ww, 0.022–9.58) showed no significant differences between age and sex groups. Notably, immature males exhibited the highest correlations with POP concentrations, particularly with the activity of carboxylesterases (CEs), suggesting a higher sensitivity than adults. These findings highlight the potential of plasmatic CEs in immature yellow-legged gulls as effective tracers of POPs exposure and effects, offering insights into the anthropogenic impacts on urban biodiversity.

A spatial analysis of urban gulls contribution to the potential spread of zoonotic and antibiotic-resistant bacteria

Wildlife human interactions within cities are becoming more common with consequences for pathogen transmission and human health. Large gulls are opportunistic feeders, adapted to coexist with humans in urban environments, and are potential vectors for spread and transmission of pathogens, including antimicrobial-resistant bacteria. We investigated the potential role that urban gulls play in the spread and dispersal of these bacteria. We analysed 129 faecal swabs from yellow-legged gulls (Larus michahellis) of different ages (56 adults and 73 immatures) during the breeding period from three years in the highly populated city of Barcelona (northeastern Spain). Thirteen individuals tested positive for the pathogenic bacteria (Escherichia coli, Listeria monocytogenes, Campylobacter jejuni), including antibiotic-resistant strains. We modelled the potential spatial spread of pathogens using the GPS trajectories of 58 yellow-legged gulls (23 adults, 35 immature individuals), which included the thirteen individuals that tested positive for pathogenic bacteria. By overlapping the spatially explicit pathogen dispersal maps with the distribution of urban installations sensitive at risk of possible pathogen spillover (e.g. elder and medical centres, markets, food industries, kindergartens, or public water sources), we identified potential areas at risk of pathogen spillover. Pathogens may be potentially spread to municipalities beyond Barcelona city borders. The results revealed that immature gulls dispersed pathogens over larger areas than adults (maximum dispersal distances of 167 km versus 53.2 km, respectively). Recreational urban water sources were the most sensitive habitats visited by GPS-tagged gulls that tested positive, followed by schools. Combining GPS movement data with pathogen analytics allows spatially explicit maps to be generated using a One Health approach that can help urban and public health management within large cities, such as Barcelona, and identify areas used by humans that are sensitive to pathogen spillover from gulls.

Gulls as Indicators of Environmental Changes in the North Atlantic: A Long-Term Study on Berlenga Island, Western Portugal

In recent decades, the breeding populations of the yellow-legged gull Larus michahellis (YLG) have increased significantly, primarily due to the increase in open refuse dumps and discards from fisheries. Portugal’s largest YLG breeding colony is located on Berlenga Island, where population numbers have been monitored since 1974. The population grew exponentially until 1994, prompting the implementation of population control measures, including culling adult birds and eggs. A long-term data base including number of breeding birds (since 1974), breeding parameters (since 2002), and trophic niches (using stable isotopes since 2011) of YLG breeding on Berlenga was related with oceanographic parameters, fish landings and quantity of urban waste. Trophic ecology showed strong relationships with oceanographic parameters (wNAO, Chl-a, and SST) and fisheries landings (the 10 most frequently consumed species by the YLG, traded at fish auctions in the main fishing harbour nearby). The results indicated significant relationships between reproductive performance and fisheries landings, particularly with demersal species that gulls primarily access through fisheries discards. However, population control measures played a pivotal role in stabilising and even reducing the population, despite sporadic events of poor oceanographic productivity in the past decade having a consistent impact on the reduction in breeding individuals.