Larus Audouinii Research Articles

A Comprehensive Microscopy Analysis of the Retina of Larus audouinii (Payraudeau, 1826): Environmental and Ecological Insights

The retinal structure is generally conserved across vertebrates; however, variations occur due to the relationship between environmental factors and visual perception. Birds have adapted to diverse ecological contexts, evolving specialized visual characteristics. In this study, we examined the retina of Audouin’s Gull (Larus audouinii) using light and transmission electron microscopy. This species is particularly intriguing as it is considered an outlier within the Laridae family: despite being a diurnal bird, it exhibits nocturnal/crepuscular foraging behaviour. Our analysis revealed a retina well adapted for diurnal activity, with features such as a retinal thickness comparable to that of other diurnal birds, a well-developed retinal pigment epithelium, and a high cone-to-rod density ratio. However, we also observed characteristics aligned with nocturnal or crepuscular activity, including a slightly increased rod density in central regions and the presence of two distinct types of horizontal cells in the inner nuclear layer. Additionally, the inner retina showed evidence of complex visual processing. These findings suggest that Audouin’s Gull is an excellent model for visual ecology studies due to its specialized adaptations.

Urban yellow-legged gull (Larus michahellis) and peri-urban Audouin's gull (Larus audouinii) as a source of Campylobacter and Salmonella of public health relevance.

Campylobacter spp. and Salmonella spp. are the leading cause of human enteric infections in the European Union. Some gull species act as reservoirs and play an important role in the epidemiology of these zoonotic agents. To gain insight into Campylobacter and Salmonella epidemiology we studied colonies of Audouin's gull (Larus audouinii) and yellow-legged gull (Larus michahellis) in Barcelona metropolitan area, Catalonia (north-eastern Spain). We assessed the occurrence, genetic diversity, virulence potential, and antimicrobial susceptibility of Campylobacter and Salmonella isolates recovered from gull faeces in different time periods within 2009-2018. The occurrence of Campylobacter was higher compared to Salmonella in both gull species. Also, the occurrence of both pathogens was significantly higher in Audouin's gull (45% for Campylobacter, 20% for Salmonella), than in yellow-legged gull (13% and 7%, respectively). All but one individual carried C. jejuni; the remaining positive yellow-legged gull carried C. lari. Salmonella serovar Typhimurium (including its monophasic variant) was the most frequent in both hosts followed by ser. Bredeney. Other serovars frequently associated with human salmonellosis (Infantis, London, Virchow) were only isolated from yellow-legged gulls. Multilocus Sequence Typing analyses showed that yellow-legged gull and not Audouin's gull carried several Campylobacter genotypes associated with human enteritis. Campylobacter isolates from both gull species revealed a high virulence potential, as opposed to Salmonella isolates which showed a lower prevalence of virulence-associated genes, particularly in Audouin's gull. Overall, a moderate to high frequency of antimicrobial resistance (including multidrug resistance) was found in both pathogens from both gull species. Campylobacter and Salmonella from yellow-legged gull showed a higher frequency of isolates resistant to antimicrobials of relevance in human medicine. Overall, our results highlight the potential public health threat associated with these gull species, particularly yellow-legged gull, in densely human populated areas.

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.

Drivers of resource allocation for breeding under variable environments in a bet hedger.

The evolutionary theory of life histories predicts that there is a trade-off between survival and reproduction: since adult survival in long-lived organisms is high, then breeding investment is more variable and more dependent on conditions (e.g. food availability and individual experience). Clutch features influence fitness prospects, but how a bet hedger builds its clutch in temporally varying environments is quite unknown. Using 27-year data on 2847 clutches of known-age breeders, we analyse how Audouin's gulls (Larus audouinii), a species showing a combination of conservative and adaptive bet-hedging breeding strategies, can allocate energy by laying clutches and eggs of different sizes. Results show that both food availability and age influenced clutch size and total egg volume in a clutch. Interestingly, we found an interaction between food and age on egg parameters: total volume in two-egg clutches, laid mostly by younger breeders, did not significantly change with food availability and the quadratic pattern in clutch size over the range of ages was less marked as long as food conditions became harsher. With increased food, females invested more by building larger first eggs, whereas they were more conservative on second and third eggs. Furthermore, asymmetries in egg volume within three-egg clutches increased with food availability for old females. Egg size profiles of two-egg clutches suggest that gulls should exhibit progressive reduction of the size of the third egg before shifting to a two-egg clutch size. Food availability influenced all parameters studied, whereas age affected the amount of energy allocated for producing eggs (their size and number) but not the way of allocating those energies (i.e. asymmetries within the clutch). Despite the range of factors affecting the clutch, results suggest that females can allocate the amount of resources in a clutch optimally to increase their fitness under variable environments via bet-hedging.

Target and untargeted screening of perfluoroalkyl substances in biota using liquid chromatography coupled to quadrupole time of flight mass spectrometry

Perfluoroalkyl substances (PFAS) are known to bioaccumulate and trigger adverse effects in marine birds. This study develops an extraction and analytical methodology for the target/untargeted analysis of PFAS in eggs of Yellow-legged gull (Larus michahellis) and Audouin's gull (Larus audouinii) and blood of Greater flamingo (Phoenicopterus roseus), which are used as bioindicators of organic chemical pollution. Samples were extracted by ultrasonication with acetonitrile and cleaned-up with activated carbon, and analysis was performed by ultra-high-performance liquid chromatography coupled to a quadrupole-time of flight mass spectrometer (UHPLC-Q-TOF) with negative electrospray ionization. Data-independent acquisition (DIA) was performed through full-scan acquisition to obtain MS1 at 6 eV and MS2 at 30 eV. In a first step, quantitative analysis of 25 PFAS was performed using 9 mass-labelled internal standard PFAS and quality parameters of the method developed are provided. Then, an untargeted screening workflow is proposed using the high-resolution PFAS library database from NORMAN to identify new chemicals through accurate mass measurement of MS1 and MS2 signals. The method permitted to detect several PFAS at concentrations ranging from 0.45 to 55.2 ng/g wet weight in gull eggs and from 0.75 to 125 ng/mL wet weight in flamingos’ blood, with PFOS, PFOA, PFNA, PFUdA, PFTrDA, PFDoA, PFHxS and PFHpA the main compounds detected. In addition, perfluoro-p-ethylcyclohexylsulfonic acid (PFECHS, CAS number 646-83-3) and 2-(perfluorohexyl)ethanol (6:2 FTOH, CAS number 647-42-7) were tentatively identified. The developed UHPLC-Q-TOF target/untargeted analytical approach increases the scope of PFAS analysis, enabling a better assessment on contaminant exposure and promoting the use of bird species as bioindicators of chemical pollution.

Results of the eighteenth winter waterbird census in Libya in 2022.

Libyan wetlands are diverse; the coastline of Libya, in particular, has different kinds of wetlands, such as salt marshes, bays, lakes, lagoons, and islands. These varieties in habitats provide good shelters and foraging sites for migratory birds during their journeys between Eurasia and Africa. Since the beginning of the Libyan winter census of waterbirds International waterbirds census (Libya IWC) in 2005, which continued regularly until 2012, it has had relatively the same performance in the number of covered sites. However, since 2013, due to the security situation that Libya has experienced due to wars and conflict, which negatively affected the quality of the IWC in Libya, the number of sites has dramatically decreased, reaching only six locations during the middle of the previous decade. The IWC 2022 aimed to count the birds along the Libyan coast from January 10 to 29. The census activities were conducted from dawn to dusk during the study period by using high-quality Telescopes, binoculars, and digital cameras for the documentation. Point transects method was used to cover the sites. The results of this year showed that a total of 64 sites were covered, and 68 species of waterbirds were counted, with an abundance of 61,850 individuals. During the census period, a total of 52 non-waterbird species found in Wetlands were recorded, and the number of individuals was 14,836 birds. A total of 18 threatened species were observed during this survey, 12 of them are mentioned in the International Union for Conservation of Nature Red List, and nine species are mentioned in the regional activities center of specially protected areas annex II as threatened in the Mediterranean, where the species; Larus audouinii (Payraudeau, 1826), Larus genei (Breme, 1839), and Puffinus yelkouan (Acerbi, 1827) are mentioned in both of them. The lack of the number of ornithologists and bird watchers is still one of the factors affecting the quality of the IWC in Libya, as well as lack of funding remains an important factor that plays a major role in the success of the waterbirds census.

Distribution and ten-year temporal trends (2009–2018) of perfluoroalkyl substances in gull eggs from Spanish breeding colonies

Gull eggs are excellent bioindicators of environmental pollution as reflect the contamination levels of coastal areas, especially of persistent and bioacumulative compounds such as perfluoroalkyl substances (PFAS). This study aims to evaluate the geographical distribution and 10-year temporal trends (2009–2018) of 17 PFAS in eggs of two gull species (Larus michahellis and Larus audouinii) from 5 main Spanish colonies. ∑PFAS ranged from 13.7 ± 5.9 to 164 ± 17 ng g−1 wet weight and higher concentrations were observed in L. audouinii than in L. michahellis. Perfluorooctane sulfonate (PFOS) was the predominant compound in all samples, followed by perfluoroundecanoic acid (PFUnA) and perfluorotridecanoic acid (PFTriDA). Perfluorododecanoic acid (PFDoA), perfluorodecanoic acid (PFDA) and perfluorooctanoic acid (PFNA) were also found in all studied areas but at lower concentrations, while perfluorooctanoic acid (PFOA) was only detected in the Medes Islands. Principal Component Analysis revealed the co-occurrence of the 6 detected PFAS, and differentiated samples from Ebro Delta and Medes Islands, both located in the North-Eastern Mediterranean Sea, with high contribution of all PFAS, from Chafarinas and Atlantic Islands with lower concentration levels and variability. Also, different patterns were observed among colonies, suggesting the fish-based diet plays an important role in PFAS bioaccumulation. In all colonies, except for the Medes Islands, ∑PFAS decreased through the 10-year study period, with PFOS, PFUnA, and PFTriDA showing a significant concentration reduction in a colony-specific manner. This study demonstrates the usefulness and importance of continuous systematic long-term monitoring to determine the geographical distribution and temporal variations of PFAS in marine protected areas using gull eggs as bioindicators of environmental pollution.

Decrease in social cohesion in a colonial seabird under a perturbation regime

Social interactions, through influence on behavioural processes, can play an important role in populations’ resilience (i.e. ability to cope with perturbations). However little is known about the effects of perturbations on the strength of social cohesion in wild populations. Long-term associations between individuals may reflect the existence of social cohesion for seizing the evolutionary advantages of social living. We explore the existence of social cohesion and its dynamics under perturbations by analysing long-term social associations, in a colonial seabird, the Audouin’s gull Larus audouinii, living in a site experiencing a shift to a perturbed regime. Our goals were namely (1) to uncover the occurrence of long-term social ties (i.e. associations) between individuals and (2) to examine whether the perturbation regime affected this form of social cohesion. We analysed a dataset of more than 3500 individuals from 25 years of monitoring by means of contingency tables and within the Social Network Analysis framework. We showed that associations between individuals are not only due to philopatry or random gregariousness but that there are social ties between individuals over the years. Furthermore, social cohesion decreased under the perturbation regime. We sustain that perturbations may lead not only to changes in individuals’ behaviour and fitness but also to a change in populations’ social cohesion. The consequences of decreasing social cohesion are still not well understood, but they can be critical for the population dynamics of social species.

Occurrence and antimicrobial resistance of zoonotic enteropathogens in gulls from southern Europe

Campylobacter spp. and Salmonella spp. are the two most frequent zoonotic bacteria involved in human enteric infections in the European Union. Both enteropathogens have been isolated from a diversity of wild birds in Northern Europe, but there is limited information about gulls as potential reservoirs in Southern Europe. A broad sampling of fledglings from nine colonies of yellow-legged gull (Larus michahellis, N = 1222) and Audouin's gull (Larus audouinii, N = 563) has been conducted in Spain and Tunisia during the late chick-rearing period. Overall, the occurrence of Campylobacter spp. and Salmonella spp. was 5.2% (93/1785, CI95%: 4.2–6.2%) and 20.8% (371/1785, CI95%: 18.9–22.7%), respectively. The most predominant Campylobacter species was C. jejuni (94.6%). A high diversity of Salmonella serovars was isolated and the most frequent were those also reported in human outbreaks, such as Salmonella Typhimurium. A high proportion of Campylobacter and Salmonella isolates showed resistance to at least one antimicrobial agent (20.2% and 51.5%, respectively), while 19.2% of Salmonella isolates were multidrug-resistant. These results show the relevance of gulls as reservoirs of Campylobacter and Salmonella by maintaining and spreading these bacteria, including resistant and multidrug resistant strains, in the environment. Our results suggest that gulls can serve as sentinel species for antibiotic pressure in the environment.

Assessment of environmental health based on a complementary approach using metal quantification, oxidative stress and trophic ecology of two gull species (Larus michahellis &Larus audouinii) breeding in sympatry

Metal pollution is currently a major issue in marine ecosystems, as organisms, and particularly seabirds, are exposed and accumulating increased levels from several anthropogenic sources. A set of 13 metals were quantified in two gull species breeding in sympatry, and in two distinct colonies separated by ca. 400 km. Oxidative stress was measured, and stable isotope analyses were used to link metal contamination and oxidative stress with the trophic ecology of each species/population. There was a clear segregation of metal contamination between the two species and to a much lesser extent between colonies. Overall, Audouin's gull was the most contaminated species for most metals, once this species relies mainly on fish and other marine resources. The Yellow-legged gull feeds regularly on terrestrial food sources besides fish, which may dilute contamination levels. Oxidative stress responses were related with birds' trophic ecology and foraging habitat, but apparently not with metal contamination.

Explorative GPS-Tracking of Foraging Movements by Audouin's Gulls Reveals No Association with Fishing Vessels in Croatia

The Audouin's Gull Larus audouinii is endemic to the Mediterranean, with the majority of the global population concentrated in Spain. It mainly feeds on small pelagic fish during the night; however, there is more variation in the foraging behaviour of the Ebro Delta population, with birds also feeding during the day and inland. This plasticity was identified as one of the main factors involved in the increase in population size since 1980. However, foraging movements have only been poorly studied in other populations. We studied the movements of Audouin's Gulls breeding in the small, endangered Croatian population, foraging at the Adriatic Sea, and compared their behaviour with that of conspecifics in the increasing Spanish population in Ebro Delta. Five incubating adults were equipped with a GPS-GSM solar-powered tracking device. We analysed characteristics of short and long foraging trips, differences in movement patterns between sexes and between night and daytime, and the association of gulls with fishing vessels. Daily average trip lengths were similar for all birds, while individual patterns were very diverse. Birds undertook both short (up to 45 km) and long-distance trips (up to 256 km), with length of trips, trip duration and the maximum distance being greater for females. The comparison of gull GPS-fixes with tracking data (VMS) of purse seine fishing vessels showed that birds from the Croatian population, in contrast to the Spanish birds, did not associate with fishing vessels, nor did their foraging behaviour change as an effect of a fishing moratorium. Our results showed that long-distance movements were longer and more frequent than those recorded in other populations, which suggests that depending on non-anthropogenic resources may result in a high cost of chick-rearing.

Telomere shortening rate predicts species life span.

Telomere shortening to a critical length can trigger aging and shorter life spans in mice and humans by a mechanism that involves induction of a persistent DNA damage response at chromosome ends and loss of cellular viability. However, whether telomere length is a universal determinant of species longevity is not known. To determine whether telomere shortening can be a single parameter to predict species longevities, here we measured in parallel the telomere length of a wide variety of species (birds and mammals) with very different life spans and body sizes, including mouse (Mus musculus), goat (Capra hircus), Audouin's gull (Larus audouinii), reindeer (Rangifer tarandus), griffon vulture (Gyps fulvus), bottlenose dolphin (Tursiops truncatus), American flamingo (Phoenicopterus ruber), and Sumatran elephant (Elephas maximus sumatranus). We found that the telomere shortening rate, but not the initial telomere length alone, is a powerful predictor of species life span. These results support the notion that critical telomere shortening and the consequent onset of telomeric DNA damage and cellular senescence are a general determinant of species life span.

A newly identified breeding site in the Aegean Sea and a status update for Audouin’s Gull Larus audouinii in Turkey (Aves: Laridae)

Audouin’s Gull Larus audouinii (Payraudeau, 1826), classified as Least Concern (LC) by the International Union for Conservation of Nature and Natural Resources (IUCN), is a pelagic bird species tha...

Temporal and Spatial Distribution of Mercury in Gulls Eggs from the Iberian Peninsula

We examined how coastal mercury contamination varied spatially and temporally across the Iberian Peninsula by measuring mercury concentrations in the eggs of the sentinel biomonitor yellow-legged gull (Larus michahellis). Samples were collected from eight colonies that ranged from the Atlantic across the south and northern areas of the Mediterranean. We also measured Hg residues in eggs of the one of the most endangered gull species in the world, the Audouin’s gull (Larus audouinii) from the Ebro Delta, where colonies of yellow-legged and Audouin’s gull co-occur. Fresh eggs were collected in 2009 and 2016 and samples were pooled from each colony for analysis. Mercury concentrations in yellow-legged gulls ranged between 0.4 and 2.8 mg/kg dry weight (dw); although there were no significant differences in concentrations between sampling periods, significant differences were found between colonies. Higher concentrations were associated with northern Mediterranean colonies (Columbretes and Ebro Delta), likely due to proximity to emission sources, circulatory marine currents and diet composition. Mercury concentrations in yellow-legged gull eggs were lower than those reported to result in impaired hatching. Residues in Audouin’s gull eggs from the Ebro Delta were significantly higher (4.0–5.6 mg/kg dw) than those in yellow-legged gull from the same location, probably associated with dietary differences. Mercury levels in Audouin’s gull were ten times above the benchmark suggested to reduce nest success by 10%. Overall, these results raise concern for adverse health impacts in this protected seabird species and further investigation in Audouin’s gull eggs from the Ebro Delta is recommended.

How fishing intensity affects the spatial and trophic ecology of two gull species breeding in sympatry

Abstract Fisheries produce large quantities of discards, an important resource for scavenging seabirds. However, a policy reform banning discards, which is soon to be implemented within the EU, will impose a food shortage upon scavengers, and it is still largely unknown how scavengers will behave. We studied the diet (hard remains), trophic (stable isotope analysis), and foraging (individual tracking) ecology of two gull species breeding in sympatry: Audouin’s gull Larus audouinii (AG) and yellow-legged gull Larus michahellis (YLG), in South Portugal, under normal fishery activity (NFA; work days) and low fishery activity (LFA; weekends), over two consecutive years. We established a pattern of dietary, spatial, and temporal segregation between the two gull species. Under LFA, yellow-legged gulls reduced their time spent at-sea, thus foraging more in alternative habitats (e.g. refuse dumps) and widening their isotopic niche (i.e. generalist behaviour). Contrastingly, Audouin’s gull had a narrower trophic niche (i.e. specialist behaviour), foraging exclusively at-sea, reducing the amount of demersal fish and increasing the amount of pelagic fish in their diet. Under NFA, both species foraged mostly at-sea, feeding almost exclusively on fish, with increased consumption of demersal species (i.e. fishery discards). In general, yellow-legged gull had a broader trophic niche (i.e. generalist behaviour) when compared with the narrower isotopic niche of Audouin’s gull (i.e. specialist behaviour). Overall, both gull species relied heavily on fishery discards. However, there was visible dietary, spatial, and temporal segregation between the two species, associated with their dietary and habitat preferences that could be attributed to the availability of anthropogenic resources, such as fishery discards.

Temporal and geographical variations of mercury and selenium in eggs of Larus michahellis and Larus audouinii from central Mediterranean islands

ABSTRACTIn this study, we determined mercury and selenium levels in abandoned unhatched eggs of the yellow-legged gull (Larus michahellis) and Audouin’s gull (Larus audouinii) collected during 2004–2005 from the Tuscan archipelago and Sardinia (Italy). The different feeding habits of the two species probably determine the different uptakes of trace elements, as the study shows highly significant differences for selenium and mercury levels as well as shell thickness and Hg:Se molar ratio values. Audouin’s gulls nesting on the coasts of the Tuscan archipelago showed significantly higher selenium levels than did gulls from colonies from the islands around Sardinia. Comparisons with a similar investigation previously conducted in the same area suggested that mercury and selenium concentrations, although in line with reports in the literature, were significantly lower than levels encountered in gulls in the early 1980s. Mercury (mg/kg d.w.) dropped from 8.631 to 5.030 in Audouin’s gulls and from 2.509 to 0.828 in yellow-legged gulls. The regional decline in mercury levels following reduced use of the metal in industry and the probable food depletion effects linked to the overfishing of fish prey of these two gull species are discussed as hypotheses that could explain the decrease in mercury levels found in eggs.

Seasonal and annual differences in the foraging ecology of two gull species breeding in sympatry and their use of fishery discards

Niche segregation between similar species will result from an avoidance of competition but also from environmental variability, including nowadays anthropogenic activities. Gulls are among the seabirds with greater behavioural plasticity, being highly opportunistic and feeding on a wide range of prey, mostly from anthropogenic origin. Here, we analysed blood and feather stable isotopes combined with pellet analysis to investigate niche partitioning between Audouin's gull Larus audouinii and yellow‐legged gull Larus michahellis breeding in sympatry at Deserta Island, southern Portugal, during 2014 and 2015. During the breeding season there was considerable overlap in the adults’ diet, as their stable isotope values of blood and primary feather (P1) did not differ, and their pellets were comprised mainly by marine fish species. However, Audouin's gulls presented higher occurrences of pelagic fish, while yellow‐legged gulls fed more on demersal fish, insects, and refuse. SIAR mixing models also estimated a higher proportion of demersal fish in the diet of yellow‐legged gulls. We also found differences between the two gull species in chicks’ feathers, suggesting that Audouin's gull adults selected prey with lower carbon isotope values to feed their young. Secondary feather (S8) of Audouin's gull presented higher isotope values compared to yellow‐legged gulls, indicating different foraging areas (δ13C) and/ or trophic levels (δ15N) between the two species in the non‐breeding season. During both the all‐year and non‐breeding periods the yellow‐legged gull showed a broader isotopic niche width than Audouin's gull in 2013, and in 2014 the two gull species exhibited different isotopic niche spaces. Our study suggests that both gull species foraged in association with fisheries during the breeding season. In this sense, a discard ban implemented under the new European Union Common Fisheries Policy may lead to a food shortage, therefore future research should closely monitor the population dynamics of Audouin's and yellow‐legged gulls.

Audouin's Gulls Larus audouinii Affected by Sublingual Fistulas

Summary. Injuries have the potential to influence individual behaviour, reproduction and/or survival. One of the least frequently observed and least known injuries in birds is sublingual fistulation, which has only been reported in four species to date. Audouin's Gull Larus audouinii is now added to this list. Based on periodical re-sightings of darvic-ringed gulls at four Mediterranean sites, the prevalence of this injury in Audouin's Gulls was estimated to be 0.13%. No negative effects of fistulas on short-term survival of injured birds were reported; the minimum survival period was 999 days. However, our findings should be treated cautiously because of the low detected incidence of this injury in free-living birds.

Consecutive cohort effects driven by density-dependence and climate influence early-life survival in a long-lived bird.

Conditions during early life, including maternal cohort effects, can influence the future fitness of individuals. This may be particularly true for long-distance migrating birds, because, apart from conditions experienced by cohorts during rearing, conditions during early life in regions far from breeding grounds may also influence their population dynamics. Very little is known about the fitness consequences of those conditions experienced by juveniles after independence, especially in wild populations and for long-lived birds. We used multi-event capture-recapture-recovery models and a unique 26-year dataset for the Audouin's gull (Larus audouinii) to assess for the first time whether survival was influenced by early conditions, both during the rearing period (i.e. a maternal cohort effect potentially affected by density dependence) and the first winter (i.e. a cohort effect driven by climate when birds disperse to wintering grounds). Our results show that juvenile survival was highly sensitive to early-life conditions and that survival decreased with stronger density dependence and harsh climate. The two consecutive cohort effects were of similar magnitude and they may represent a selection filter. Thus, early-life conditions had a strong impact on survival, and neglecting this complexity may hinder our understanding on how populations of long-lived animals fluctuate and respond to perturbations.

Influence of trophic ecology on the accumulation of dioxins and furans (PCDD/Fs), non-ortho polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in Mediterranean gulls (Larus michahellis and L. audouinii): A three-isotope approach

The impact of pollution caused by severe anthropogenic pressure in the Mediterranean Sea, an important biodiversity hotspot, requires continuous research efforts. Sources of highly toxic chemicals such as Persistent Organic Pollutants (POPs) are misunderstood in representative Mediterranean species, which limits our capability to establish proper conservation strategies. In the present study, eggs of Audouin's and yellow-legged gulls (Larus audouinii and L. michahellis) were used to investigate the trophic sources, as measured by δ13C, δ15N, and δ34S, of legacy POPs, in particular, polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and non-ortho polychlorinated biphenyls (no-PCBs), as well as recently-regulated POPs, e.g., polybrominated diphenyl ethers (PBDEs). Special attention was paid to the usefulness of rarely-explored δ34S ratios in explaining POP exposure in wildlife, and δ34S was the isotopic ratio that best explained POP variations among gulls in most cases, thus demonstrating its usefulness for understanding POP exposure in wildlife. Significant relationships between stable isotope signatures and POP concentrations revealed increasing levels of no-PCBs and low halogenated PCDD/Fs and PBDEs in Mediterranean gulls as the consumption of marine resources increases. In contrast, highly chlorinated and brominated congeners appeared to preferentially accumulate in gulls feeding primarily on refuse from dump sites and terrestrial food webs. The use of suitable dietary tracers in the study of POPs in yellow-legged gulls revealed the importance of dump sites as a source of POPs in Mediterranean seabirds, which has not previously been reported. In contrast, the preferential accumulation through marine food webs of low chlorinated PCCD/Fs and no-PCBs, which show the highest toxic equivalents factors (TEFs), led to a significantly greater toxicological concern in Audouin's as compared to yellow-legged gulls. Audouin's gull exposure to POPs appears primarily related to the pelagic food webs commonly exploited by fisheries, highlighting the need for further research given the potential impact on human consumption.