Larus Michahellis Research Articles

Changes in plastic ingestion by yellow-legged gulls (Larus michahellis) over the breeding season

Gulls can be particularly vulnerable to ingesting plastics when using anthropogenic food sources, with potential consequences for survival and reproductive success. Although birds are known to switch foraging habitats over the breeding season to provide higher quality food for chick provisioning, it is unclear what this means regarding the ingestion of plastics. Here, we tested whether breeding gulls decrease the amount of plastic ingested during reproduction by collecting pellets from a series of monitored nests at a large yellow-legged gull (Larus michahellis) colony in southern France. We found at least one plastic item in 83.9 % of the analyzed pellets, with the most abundant plastic type being polyethylene-based sheet plastic. As predicted, we found a slight decrease in the number of plastic items in pellets at chick hatching. These results suggest that gulls, like other birds, may adjust foraging habits to provide more digestible, less risky, food to chicks.

Movement patterns of immature Yellow-legged Gulls Larus michahellis from Gran Canaria, Canary Islands

The Yellow-legged Gull subspecies Larus michahellis atlantis is thought to be resident in the Macaronesia islands, however, the movement patterns of the population remain largely unknown. We conducted an eight-year (2010–19) ringing and re-sighting program on the island of Gran Canaria (GC), Canary Islands, with an aim of estimating the movement patterns of its gull populations. Re-sighting data revealed that most gulls were observed within 50 km of their natal sites; the farthest locality where studied gulls were seen was Dakhla (500 km from GC) in northwestern Africa. Our findings are compatible with the Yellow-legged Gulls adopting either a GC residency with some dispersal to other islands within the Canary Islands archipelago or to northern Africa, or a true partial migration strategy. Return to GC by some of the gulls that were observed outside GC suggests that philopatry to their natal site could be high, though this should be the focus of further investigation.

Breeding Biology of the Yellow-legged Gull (Larus michahellis, Naumann, 1840): a Small Island Population in Southwestern Türkiye

Urbanization and fisheries affected a rapid increase in seagull populations in western Mediterranean populations of the yellow-legged gull. The main reason is the increased food resources such as fisheries, big ports, and dumps. In this study, we aimed to understand and to compare the breeding biology of the yellow-legged gull in eastern Mediterranean. We studied on the small island in southwestern Türkiye between 2013 and 2015. All nesting sites were determined, marked, and monitored once a week. The breeding season has started in late February, nesting and laying eggs have started at the beginning of March, and they left the island in the second half of June after fledging. The incubation period is 29.17±2.85 days, only one clutch in a season and 2 or 3 eggs were laid in the nests. There was a slight increase in the number of pairs and nests between years but there is no significant difference in all parameters such as laying date, clutch size, hatching and fledging success in Pırasalı Island population and the rate of both hatching and fledging success are lower than western Mediterranean populations. While predation is the weakest factor for lower breeding success, intraspecific predation may be the factor but the main effect is the lower food abundance for the hatchlings.

Helminth Parasites of Yellow-Legged Gull Larus michahellis (Charadriiformes) from Bursa, Turkey

The yellow-legged gull, Larus michahellis, is a common gull that exists in Europe, the Middle East, and North Africa. Their broad diet makes them especially susceptible to a variety of helminths. We conducted a survey of intestinal helminths of L. michahellis to determine the diversity of intestinal parasites. Thirty-five yellow-legged gulls were necropsied, and helminths were examined via light microscopy. Twenty-three of 35 (65%) of hosts examined were infected with the following helminths: 6 Digenea species (Acanthotrema armata, Brachylaima aspersae, Cryptocotyle lingua, Diplostomum spathaceum, Knipowitschiatrema sp., and Stephanoprora denticulata); 5 Cestode species (Alcotaenia microcantha, Diphyllobothrium dentriticum, Microsomacanthus ductilis, Monopylidium galbulae, and Tetrabothrius erostris); and 2 Nematode species (Contracaecum rudolphii and Synhimanthus sp.). Herein, the intestinal parasite diversity of yellow-legged gulls from Turkey is reported, and new geographical records are documented.

Correlation between seabirds and fisheries varies by species at fine-scale pattern

Abstract Understanding how fisheries influence seabird distribution is critical in the development of sustainable fisheries management. Species distribution models were applied to analyse the influence of the fishing footprint, discards, and oceanographic factors on seabird attendance patterns to trawlers in the Gulf of Cádiz. More than 30 species of seabirds were attracted to trawlers, although only seven were registered with relatively high frequency and abundance. For these species, fishery footprint was a good predictor for the distribution of four out of seven (yellow-legged gull, lesser black-backed gull, northern gannet, and Cory's shearwater). Yellow-legged and lesser black-backed gull flocked in large numbers to trawlers, mostly in shallow areas where they were also attracted by purse seines. Northern gannets and Cory's shearwaters appeared with relatively high frequency and their distributions correlated with trawler effort and abundance of potential prey discards. Balearic shearwaters were attracted in low numbers and concentrated in shallow areas, where potential prey discards were also more abundant. For these three species, discards as surrogate of natural prey distribution were good predictors of trawler attendance. Our research revealed that, at a local scale, the degree of interaction of seabirds on fishing discards varies by species. Therefore, fine-scale studies are essential in identifying interactions between seabirds and fisheries, and thus assessing conservation issues such as bycatch or the consequences of discard bans.

Sunlight and lifestyle: linking prenatal light conditions and personality development in a wild bird

Even though personality is a major determinant of individual survival, the development of animal personality traits is still poorly understood. Beyond an individual's genetic background, personality may be shaped by the conditions experienced during embryonic development. Light is a salient and variable ecological factor that can affect organismal physiology, establish brain asymmetries and ultimately modulate postnatal phenotypes across multiple taxa. Exposure to light is known to vary among avian embryos due to changes in parental incubatory constancy, but whether differences in the prenatal light environment can influence offspring personality development has rarely been explored. Here, we investigated whether the prenatal light environment shapes a key dimension of animal personality, the shy–bold axis, in hatchlings of a semiprecocial seabird, the yellow-legged gull, Larus michahellis . In gulls, the prenatal light environment may be especially important for last-laid eggs, as parental attendance during late incubation is more variable for last-laid than for senior eggs. We manipulated the levels of embryonic exposure to light (within the natural range previously documented in the wild) during the last stages of egg incubation and assessed differences in boldness in newly hatched junior chicks. We then used structural equation modelling to explore whether the effect of prenatal light exposure on the shy–bold axis is linked to the establishment of brain asymmetries (lateralization) and/or changes in plasma corticosterone levels. Prenatal light exposure promoted bolder phenotypes in gull chicks, which may improve their individual performance when competing for parental resources. Prenatal light also promoted the lateralization of the begging behaviour in newly hatched chicks, which was negatively associated with boldness. Finally, light induced changes in glucocorticoid levels, but these changes did not impact chicks' personality. Our findings unambiguously confirm that the prenatal light environment strongly affects the development of shy–bold phenotypes in gull hatchlings through a complex multipath mechanism. • Can the prenatal environment shape animal personality? • Last-hatched gull eggs are highly exposed to sunlight during late incubation. • We explored whether prenatal exposure to light shapes boldness in hatchlings. • Prenatal light promoted bold phenotypes and brain lateralization in gull chicks. • These adjustments might improve chick performance under competitive disadvantage.

Maternal testosterone affects offspring telomerase activity in a long-lived seabird.

Androgens are a group of steroid hormones that have long been proposed as a mechanism underpinning intergenerational plasticity. In birds, maternally allocated egg testosterone, one of the main androgens in vertebrates, affects a wide variety of offspring phenotypic traits but the mechanisms underlying this form of intergenerational plasticity are not yet well understood. Recent in vitro and animal model studies have shown that telomerase expression and activity are important targets of androgen signaling. The telomerase enzyme is known for its repair function on telomeres, the DNA–protein complexes at the ends of chromosomes that are involved in genomic integrity and cell aging. However, the role of maternal testosterone in influencing offspring telomerase levels in natural populations and its consequences on telomere length and potentially on offspring development is still unknown. Here, by experimentally modifying the level of egg testosterone in a natural population of yellow‐legged gull (Larus michahellis), we show that chicks hatched from testosterone‐treated eggs had higher average levels of telomerase and faster growth than controls during the first week of life. While testosterone‐treated chicks also tended to have longer telomeres than controls at hatching this difference disappeared by day 6 of age. Overall, our results suggest that maternal testosterone may have a potential adaptive value by promoting offspring growth and presumably telomerase levels, as this enzyme plays other important physiological functions (e.g., stress resistance, cell signaling, or tissue genesis) besides telomere lengthening. Nonetheless, our knowledge of the potential adaptive function of telomerase in natural populations is scarce and so the potential pathways linking maternal hormones, offspring telomerase, and fitness should be further investigated.

Light received by embryos promotes postnatal junior phenotypes in a seabird

Abstract Light is a salient and variable ecological factor that can impact developmental trajectories of vertebrate embryos, yet whether prenatal light environment can act as an anticipatory cue preparing organisms to cope with postnatal conditions is still unclear. In asynchronous birds, last-laid eggs are particularly exposed to sunlight as parental incubation behavior becomes intermittent after the hatching of senior chicks. Here, we explore whether natural variations in prenatal light exposure shape the distinctive phenotype showed by last-hatched chicks of a semi-precocial seabird, the yellow-legged gull (Larus michahellis), potentially preparing them to cope with the postnatal competitive context. To do this, we manipulated the amount of light received by last-laid eggs (within a natural range) during last stages of embryonic development. Prenatal exposure to light cues promoted the development of the resilient “junior phenotype” exhibited by last-hatched gull chicks, characterized by accelerated hatching, increased begging behavior and a slower growth rate. These developmental and behavioral adjustments were accompanied by down-regulation of genes involved in metabolism and development regulation (SOD2 and TRalpha), as well as changes in the HPA-axis functioning (lower baseline corticosterone and robust adrenocortical response). Junior chicks exposed to light cues during the embryonic development showed longer telomeres during the early postnatal period, suggesting that light-induced adjustments could allow them to buffer the competitive disadvantages associated with hatching asynchrony. Our study provides evidence that postnatal junior phenotypes are, at least in part, prenatally shaped by light cues that act during a critical temporal window of developmental sensitivity.

Plenty of rooftops with few neighbours occupied by young breeding Yellow‐legged Gulls (Larus michahellis): Does this occur at the expense of their health condition?

Gulls, as largely flexible opportunistic individuals, have been increasingly breeding in many cities around the world, but it is still unclear whether urban habitats are of equal or higher quality than traditional natural habitats or represent an ecological trap with immediate reproductive benefits but longer‐term detrimental consequences to health. Here we present a study of breeding parameters (nest density, egg dimensions, clutch size, hatching success and adult body condition) and physiological parameters (erythrocyte sedimentation rate, heterophil/lymphocyte ratio, haemoglobin concentration and measurements of oxidative stress) as indicators of the general health condition of Yellow‐legged Gull Larus michahellis adults and chicks from natural and urban colonies. Yellow‐legged Gulls in the largest urban area (Porto) laid smaller eggs and clutches, showed a significantly lower occurrence of inflammatory processes in chicks, and showed a slower early chick growth than in the natural colony of Deserta. This suggests that urban gulls might be facing important trade‐offs between the advantages of breeding in lower density urban colonies, with fewer intraspecific interactions and a lower disease transmission probability, and the disadvantages of having an anthropogenic diet usually lower in nutritional value.

Disturbance‐dependent Yellow‐legged Gull (Larus michahellis) predation on Larid chicks decreases with chick age

Predation is one of the key factors shaping the dynamics of animal populations. In birds, nest loss due to predation can be a significant cause of low reproductive success. Ground‐nesting birds are among the bird groups most susceptible to predation, mainly because their nests are easily accessible to a broad suite of potential predators. For these birds, anthropogenic disturbances can generate changes in nest predation risk by altering their antipredator behaviour and also by altering the behaviour of the predator species, i.e. the predator becoming much more aware of predation opportunities due to frequent disturbances and/or motivated to repeat predation attempts when some are successful. To date, most previous studies investigating this have focused on a single effect, either predation or disturbance, on chick survival. It remains unknown how the risk of predation with and without disturbance varies with chick age. In this study, we used behavioural observations to assess how the interaction between predators and disturbance affects predation risk in chicks and how this interacts with chick age. Specifically, we investigated the effect of disturbance caused by humans and stray dogs on the predation of Slender‐billed Gull Chroicocephalus genei chicks by Yellow‐legged Gulls Larus michahellis, and whether this depended on the age of the chicks. Our results revealed that disturbance had a significant positive effect on predation measures of Slender‐billed Gull chicks by Yellow‐legged Gulls, but that this effect was mediated both by disturbance type and the age of chicks. Stray dogs entering the colony had a stronger disturbance effect on chicks than passing humans, increasing predation risk by Yellow‐legged Gulls. Our results also showed that chick age interacts with disturbance type to determine the predation risk. This is probably mediated by chicks' capacity to escape predation by gathering in a single large crèche that runs into the water when disturbed. To preserve Slender‐billed Gull colonies in one of its few remaining breeding sites in Tunisia, and as gulls tend to react even when the disturbance occurs relatively far from the colonies, it is crucial to (1) restrict human access to dikes and islets where large colonies breed and (2) construct artificial islets attractive to gulls and inaccessible to stray dogs.

Age-related differences in foraging behaviour at sea and interactions with fishing vessels in an opportunistic urban gull

Abstract Fishing activity generates high amounts of fishing discards, a predictable anthropogenic food subsidies used by seabirds. Although the use of discards by these predators has been well studied, there is a lack of knowledge about the ontogenetic differences in their use. We contributed to filling this gap for the yellow-legged gull (Larus michahellis), an opportunistic predator that extensively exploits anthropogenic food subsides. We investigated its foraging behaviour during the early breeding season deploying GPS devices on adults, immatures, and juveniles from the urban population of Barcelona (northwestern Mediterranean Sea) and examining the effect of fishing vessels on their spatial movements using a Vessel Monitoring System. The results revealed age-related differences in distribution and foraging behaviour at sea and an interaction with fishing vessels in this seabird. Age-related differences in behaviour were explained by the reproductive constraints of adults and the ontogenetic differences associated with lower foraging ability in immature and juvenile individuals. We did not find apparent preferences for a specific type of fishing vessel between ages. These results suggest that the reform of the Common Fisheries Policy might affect the entire population of this species, that could lead to an increase in the use of urban environments, increasing the conflicts with human activities.

Sex determination based on morphometric measurements in yellow-legged gulls (Larus michahellis) around Istanbul

BackgroundYellow-legged gulls (Larus michahellis), commonly found in Istanbul and their surroundings, have a monomorphic plumage, like other gull species. For this reason, sex determination cannot be made externally. In this study, a total of 60 adult Yellow-legged gulls, 33 males, and 27 females, collected from the coastal areas of Istanbul, were examined. Discriminating functions were developed to classify males and females using birds that were previously sexed by DNA analysis and abdominal dissection.ResultsHead length and bill depth were selected to build the discriminant function by the stepwise analysis. The function classified male gulls with an accuracy of 97.0% and females with an accuracy of 92.6%. Head length alone is the most accurate predictor in terms of the percentage of correct sex determination (90.9% for males, 92.6% for females).ConclusionsFunctions that can easily determine sexual dimorphism for the population of Larus michahellis gulls around Istanbul have been put forward for the first time.

Blood mercury concentrations in four sympatric gull species from South Western France: Insights from stable isotopes and biologging

Mercury (Hg) is a toxic trace element widely distributed in the environment, which particularly accumulates in top predators, including seabirds. Among seabirds, large gulls (Larus sp) are generalist feeders, foraging in both terrestrial and marine habitats, making them relevant bioindicators of local coastal Hg contamination. In the present study, we reported blood Hg concentrations in adults and chicks of four different gull species breeding on the French Atlantic coast: the European herring gull (Larus argentatus), the Lesser black-backed gull (L. fuscus), the Great black-backed gull (L. marinus) and the Yellow-legged gull (L. michahellis). We also investigated the potential role of foraging ecology in shaping Hg contamination across species, using the unique combination of three dietary tracers (carbon, nitrogen and sulfur stable isotopes) and biologging (GPS tracking). A high concentration of Hg was associated with high trophic position and a marine diet in gulls, which was corroborated by birds’ space use strategy during foraging trips. Adults of all four species reached Hg concentrations above reported toxicity thresholds. Specifically, adults of Great black-backed gulls had a high trophic marine specialized diet and significantly higher Hg concentrations than the three other species. Blood Hg was 4–7 times higher in adults than in chicks, although chicks of all species received mainly marine and high trophic position prey, which is expected to be the cause of blood Hg concentrations of toxic concern. By using both stable isotopes and GPS tracking, the present study provides compelling insights on the main feeding habits driving Hg contamination in a seabird assemblage feeding in complex coastal environments.

Multiresistant Enterobacteriaceae in yellow-legged gull chicks in their first weeks of life.

Wild animal species living in anthropogenic areas are commonly carriers of antimicrobial‐resistant bacteria (AMRB), but their role in the epidemiology of these bacteria is unclear. Several studies on AMRB in wildlife have been cross‐sectional in design and sampled individual animals at only one point in time. To further understand the role of wildlife in maintaining and potentially transmitting these bacteria to humans and livestock, longitudinal studies are needed in which samples are collected from individual animals over multiple time periods. In Europe, free‐ranging yellow‐legged gulls (Larus michahellis) commonly live in industrialized areas, forage in landfills, and have been found to carry AMRB in their feces. Using bacterial metagenomics and antimicrobial resistance characterization, we investigated the spatial and temporal patterns of AMRB in a nesting colony of yellow‐legged gulls from an industrialized area in southern France. We collected 54 cloacal swabs from 31 yellow‐legged gull chicks in 20 nests on three dates in 2016. We found that AMRB in chicks increased over time and was not spatially structured within the gull colony. This study highlights the complex occurrence of AMRB in a free‐ranging wildlife species and contributes to our understanding of the public health risks and implications associated with ARMB‐carrying gulls living in anthropogenic areas.

Food versus Disturbance: Contradictory Effects of Human Activities on an Opportunistic Seabird Breeding in an Oligotrophic Marine System

The islands of the Aegean Sea are areas of high biodiversity and endemism and harbor globally important seabird communities. Resident seabirds breed on offshore islands, where they often form strong nesting colonies. Breeding seabirds are important determinants of an island’s ecosystem function while also being exposed to a plethora of human activities. Understanding how anthropogenic activities impact such populations is not just essential for seabird conservation but is also critically important for the management of small insular ecosystems and the native species communities they support. We quantify the effect of human activities on the size and locations of Yellow-legged Gull (Larus michahellis) colonies from the Cyclades and Sporades archipelagos. We gathered data on variables suspected to influence seabird colonies, including physical islet characteristics, resource availability, and type and extent of human disturbance. Analyses were conducted on the local (islet) and on the regional (island cluster) levels to identify proximate and ultimate factors shaping the breeding population sizes of resident colonies. On the local level, we identify a clear negative effect of the presence of invasive rats on gull nesting density. Similarly, the presence of feral grazing mammals such as goats and rabbits has negative impacts on gull populations, an effect that appears to be primarily mediated through nest disturbance. Access to landfills and fishing vessels both had positive impacts on gull nesting density. Our results suggest approaches to managing Yellow-legged Gull populations in the Mediterranean Basin by taking into consideration the roles of introduced mammals, fishing activities, and open-air landfills on seabirds in the region.

Recent large-scale philophthalmosis outbreak in Portugal: inefficacy of common antihelminthic agents

BackgroundParasitic conjunctivitis caused by Philophthalmus spp. is a common ophthalmic disease in birds, with localized outbreaks occurring worldwide. There is no consensus on treating this disease; mechanical removal is considered a standard recommendation, but is associated with disease relapses within days or weeks.MethodsFrom 2015 to 2020, we examined 4295 Larus michahellis and Larus fuscus gulls in southern Portugal for the presence of Philophthalmus spp. Due to the need to treat dozens of infected gulls in the rescue station, we tested three treatment regimens aimed at targeting Philophthalmus lucipetus in the infected gulls: (I) the ophthalmic application of levamisole; (II) the oral application of milbemycin in combination with praziquantel; and (III) the subcutaneous application of ivermectin.ResultsThe outbreak of philophthalmosis in gulls in southern Portugal has been ongoing since the first cases were reported in 2015–2016. The prevalence of philophthalmosis has fluctuated annually, peaking a maximum of 10.3% in L. fuscus in 2017 and at 2.1% in L. michahellis in 2016. The infection intensity peaked at a median of 11.5 eye-flukes per host bird in L. fuscus in 2016 and a median of six eye-flukes per host bird in L. michahellis in 2017. Nine gulls were infected with >50 eye-flukes. None of the treatment options were effective at treating P. lucipetus infections: the numbers of eye-flukes in the infected birds did not decrease, and the clinical signs of the disease did not change.ConclusionsAn outbreak of philophthalmosis in southern Portugal has massively affected two species of gulls in the region. Two previously suggested philophthalmosis treatments (ocular levamisole and praziquantel given orally), as well as a third mode of treatment with a previously failed compound (ivermectin administered subcutaneously) were used. However, the treatments did not affect the numbers of P. lucipetus in the eyes of the treated gulls. Further research should address ophthalmic gel formulations or sub-conjunctival delivery mode for antihelminthic drugs that are effective against Philophthalmus spp. in vitro.Graphical abstract

Heavy metals and metalloid levels in the tissues of yellow-legged gulls (Larus michahellis) from Spain: sex, age, and geographical location differences

In the present study, mercury (Hg), cadmium (Cd), lead (Pb), selenium (Se), and arsenic (As) were measured in liver, kidney, and feathers of adult, juvenile, and chick seagulls (Larus michahellis) collected from the northwest of Spain. Age, sex, and the geographical location of samples were considered variables that can influence metal bioaccumulation, for which concentrations were determined by means of ICP-MS. The mean concentrations (dry weight) found in seagulls were 7.01 ± 0.37 mg Hg/kg, 22.82 ± 2.83 mg Cd/kg, 7.36 ± 1.36 mg Pb/kg, 18.64 ± 0.63 mg Se/kg, and 10.64 ± 0.59 mg As/kg. Regarding the different factors analyzed, Hg was the only metal showing sex-related differences, being significantly higher (p < 0.05) the concentrations found in feathers of males (1.26 ± 0.12 mg/kg) than those in females (0.99 ± 0.11 mg/kg). A highly significant (p < 0.01) increase in levels of some metals was found in liver related to the increase of age: Hg (adults (A) 3.33 ± 0.22 mg/kg vs chicks (C) 1.76 ± 0.28 mg/kg), Cd (A 4.74 ± 0.62 mg/kg vs C 1.79 ± 0.2), Pb (A 0.65 ± 0.12 mg/kg vs juveniles 0.4 ± 0.11 mg/kg), and Se (A 7.56 ± 0.43 mg/kg vs C 5.24 ± 0.53 mg/kg). Positive correlations between Cd-Hg and Se–Hg were found in liver (p < 0.001), kidney (p < 0.001), and feathers (p < 0.05 and p < 0.001, respectively). The associations found may reflect antagonistic interactions between Se and Cd on Hg toxicity. The results suggest that L. michahellis can reveal local contamination around the foraging and breeding sites and can be a very useful monitoring instrument for assessing heavy metal contamination and sentinel species of environmental health.

The Rapid Effects of Yellow-Legged Gull (Larus michahellis) Colony on Dune Habitats and Plant Landscape in the Atlantic Islands National Park (NW Spain)

The Atlantic Islands of Galicia Maritime/Terrestrial National Park hosts one of the largest breeding colonies of yellow-legged gull (Larus michahellis) in the world. In 2002, a new yellow-legged gull breeding colony was established on the Punta Muxieiro dune complex, which also harbors rare and threatened plant species and habitat types of community interest according to Directive 92/43/EEC. This study assesses the effect of this colony on two habitats of community interest: white dunes and grey dunes. For this purpose, plant cover and soil properties, composition, and nutrient content were monitored in plots with different gull densities. Moreover, historic aerial images were compiled to observe changes in the plant landscape of the dune system. The results showed that, despite the recentness of the occupation of the dune system by yellow-legged gull species, significant changes in acidic–alkaline processes and nutrient availability were already observed in soils. Soils in plots with higher gull density showed more acidic pH values and a higher content of the most labile N and P fractions. Moreover, a decrease in plant cover and number of species was also demonstrated in plots with higher gull densities. Finally, the presence of ruderal and alien species such as Urtica membranacea and Parietaria judaica was also observed.

Gulls living in cities as overlooked seed dispersers within and outside urban environments

The yellow-legged gull is an opportunistic and generalist bird that has colonised urban areas, where it has found very favourable trophic resources but also causes disturbance to humans and damage to infrastructure. Here, we investigated the potential role that gulls play in the dispersal of plants in Barcelona, a highly populated city of north-eastern Spain. We analysed the stomach contents of 145 chicks collected in urban nests and reported the presence of seeds of 27 plant taxa. We then developed a plant dispersal model based on the movements of 20 GPS-tracked yellow-legged gulls breeding in the city of Barcelona. We estimated seed dispersal distances, seed shadows and percentage of seeds reaching habitats suitable for seeds regurgitated in pellets and those excreted in faeces. Seven of the 27 plant taxa found in the stomachs were alien taxa to Spain. Average dispersal distances of plant seeds by gulls were around 700 m, but maximum dispersal distances reached up to 35 km. Dispersal distances and seed spatial patterns did not differ between faeces and pellet models, as most strongly depended on gull movements. About 95% of the seeds were dispersed within urban environments and between 20 and 30% reached suitable habitats for seed deposition (urban woodlands, green urban parks and urban grasslands). Urban gulls frequently dispersed seeds (including alien species) within urban habitats, both via direct consumption or via secondary dispersal after consuming granivorous birds that had ingested the seeds, such as pigeons or parakeets. Urban planning for Barcelona is based on native plant species, and thus, special attention should be paid to alien plants dispersed by birds, which could pose a risk to native biodiversity in urban ecosystems.

Comparing scavenging in marine and terrestrial ecosystems: a case study with fish and gull carcasses in a small Mediterranean island

Carrion consumption by scavengers is a key component of both terrestrial and aquatic food webs. However, there are few direct comparisons of the structure and functioning of scavenging communities in different ecosystems. Here, we monitored the consumption of 23 fish (seabream Sparus aurata) and 34 bird (yellow-legged gull Larus michahellis) carcasses on a small Mediterranean island (Isla Grosa, southeastern Spain) and surrounding waters in summer to compare the structure of the scavenger assemblages and their carrion consumption efficiencies in terrestrial and shallow water habitats. Scavenging was highly efficient both in marine and terrestrial environments, especially in the presence of a highly abundant vertebrate scavenger species, the yellow-legged gull. The vertebrate scavenger community was richer in the marine environment, whereas the invertebrate community was richer on land. The scavenger network was usually well-structured (i.e., nested), with the exception of the community associated with fish terrestrial carcasses, which were almost monopolized by yellow-legged gulls. In contrast, gulls left conspecific carcasses untouched, thus allowing longer persistence of gull carcasses on land and their exploitation by a diverse insect community. Our study shows important differences in the scavenging process associated with environment and carcass type. Promising avenues for further eco-evolutionary and applied research arise from the comparison of scavenging processes in terrestrial and marine ecosystems, from small islands to continents.