Black-headed Gull Chroicocephalus Ridibundus Research Articles

Age differences in primary moult of the Black-headed Gull Chroicocephalus ridibundus

Flight feather moult is an energetically expensive stage of the annual cycle of birds. Its timing is adjusted to other important time- and energy-demanding activities, including migration. In the vast majority of migratory birds, primary moult occurs before or after migration or moulting is suspended during migration. The Black-headed Gull is an exception: it starts moulting flight feathers at the onset of the autumn migration. The course of primary moult in this species is still poorly understood due to the difficulty in obtaining sufficient data from the entire period of flight feather replacement. In this paper, we employed digital photos taken in the field to estimate the start, variation in the start date and duration of primary moult in adult and immature Black-headed Gulls, by using the Underhill–Zucchini likelihood moult model. On average, immatures started their moult on 7 June, 25 days earlier than adults, but their moult lasted 5 days longer. Consequently, there was a 20-day difference in the end of moult – that is, on average it occurred on 16 September and 6 October in immature and adult gulls, respectively. Adults showed greater variability in the mean primary moult start date than immatures, as the beginning of flight feather replacement may depend on breeding success (earlier after breeding failure) and on breeding phenology. The overlap of primary moult and migration produces a trade-off in resource allocation between those two processes, which leads to a low number of simultaneously growing primaries and a decrease in the growth rate of the two external, heaviest flight feathers. Existing reports of a later completion of primary moult in the first half of November in this species are based on the faulty assumption that the outermost primary is always the longest, which is not the case in 34% of individuals.

Population size and nesting peculiarities of the black-headed gull Chroicocephalus ridibundus (Linnaeus, 1766) on the territory of water treatment facilities

Background. Today, the black-headed gull inhabits man-made areas of wastewater treatment facilities (WTF) to comensate for the the reduction of natural aquatic and wetland habitats. Over the last decade, a nearly tenfold increase in its population has been recorded, despite a low reproduction rate. This fact indicates the lack of stability in the bird population, necessitating thorough research. Materials and Methods. The analysis of the population size and biological charac­teristics of black-headed gulls involved censuses and observations at the WTF of the city of Kharkiv using conventional methods during the spring-summer periods of 2020–2021 and 2023. Results. The population of the black-headed gull reached its peak in the third decade of May 2020 (2637 individuals) and 2023 (2124 individuals), as well as in the second decade of May 2021 (3949 individuals). The maximum nesting density was observed on sludge sites (SS) of wastewater treatment facilities that are most similar to natural habitats, where dried mud alternates with water patches and vegetation at the bottom and around the perimeter (Type V): 236.7±26.7 pairs/ha in 2020 and 242.9±28.5 pairs/ha in 2021. The majority of nests were found in the first decade of May 2021 and the third decade of May 2020. The black-headed gull forms mixed-species, occasionally monospecific subcolonies. Nesting in association with it were: Sterna hirundo, Anas platyrhynchos, Spatula clypeata, Vanellus vanellus, Charadrius dubius, Himantopus himantopus, Fulica atra, Gallinula chloropus, and Aythya ferina. The size of the complete black-headed gull clutch was 3.1±0.4 eggs (n = 190). The egg dimensions were 50.9±2.1 ´ 36.2±1.1, with a mass of 34.6±2.8 g. Regarding shell coloration, five types of background colors were identified. Mass egg laying occurred from the third decade of April to the first decade of May, constituting 40.3 % (n = 993) in 2020 and 62.3 % (n = 1757) in 2021. The egg-laying period extended from April to July, with the latest non-incubated clutches recorded in the first decade of July (3.07.2020). The first chicks were found in nests in the first decade of May, while mass hatching occurred in the second half of May. The latest registration dates of the birds on nesting territories were in the second decade of July for 2020 and 2023, and the first decade of August for 2022. The nesting season duration varied from 125 to 140 days in different years. Autumn migration commenced with summer relocations and concluded from late October to early November. The reproductive success – the percentage of nestlings that fledged and successfully achieved flight – constituted 29.2 % (n = 2404 of laid eggs) in 2020, and 15.5 % (n = 6138) in 2021. The majority of offspring perished due to changes in water levels (prolonged rainfall or industrial wastewater discharge), predation, disturbance factors, etc. Conclusion. The colonial nesting of the black-headed gull creates favorable conditions for the habitation and reproduction of various bird species, including rare ones, which is essential for their conservation.

Mercury stable isotopes in seabirds in the Ebro Delta (NE Iberian Peninsula): Inter-specific and temporal differences

Mercury (Hg) is a global pollutant, which particularly affects aquatic ecosystems, both marine and freshwater. Top-predators depending on these environments, such as seabirds, are regarded as suitable bioindicators of Hg pollution. In the Ebro Delta (NE Iberian Peninsula), legacy Hg pollution from a chlor-alkali industry operating in Flix and located ca. 100 km upstream of the Ebro River mouth has been impacting the delta environment and the neighboring coastal area. Furthermore, levels of Hg in the biota of the Mediterranean Sea are known to be high compared to other marine areas. In this work we used a Hg stable isotopes approach in feathers to understand the processes leading to different Hg concentrations in three Laridae species breeding in sympatry in the area (Audouin's gull Ichthyaetus audouinii, black-headed gull Chroicocephalus ridibundus, common tern Sterna hirundo). These species have distinct trophic ecologies, exhibiting a differential use of marine resources and freshwater resources (i.e., rice paddies prey). Moreover, for Audouin's gull, in which in the Ebro Delta colony temporal differences in Hg levels were documented previously, we used Hg stable isotopes to understand the impact of anthropogenic activities on Hg levels in the colony over time. Hg stable isotopes differentiated the three Laridae species according to their trophic ecologies. Furthermore, for Audouin's gull we observed temporal variations in Hg isotopic signatures possibly owing to anthropogenic-derived pollution in the Ebro Delta. To the best of our knowledge this is the first time Hg stable isotopes have been reported in seabirds from the NW Mediterranean.

A case of polymelia in the Black-headed Gull Chroicocephalus ridibundus

Polymelia is a malformation consisting of the presence of supernumerary limbs. Although relatively common in farm animals and anurans, it is quite rare in wild vertebrates and, especially, birds. I describe here the case of a Black-headed Gull Chroicocephalus ridibundus seen in Barcelona (Catalonia, NE Spain) in January and February 2023 that had an atrophic leg originating from the distal posteromedial part of its right tibiotarsus. It was a healthy-looking bird, apparently in its second winter, and showed normal behaviour with no visible signs of any other pathology or malfunction. We are only aware of one previous case of polymelia in gulls and this is the first time it has been reported in a Black-headed Gull. It is also good example of survival in a bird affected by polymelia.

Habitat use across the tidal cycle by black-headed gulls breeding in the Wadden Sea

Movements of birds foraging in intertidal areas are often strongly linked to the tidal cycle, as water levels determine where and when birds can forage. The strength of this link likely depends on the ability to forage in habitats other than intertidal areas and on constraints imposed by breeding duties. Few studies have focused on the use of intertidal areas by generalists, such as the black-headed gull Chroicocephalus ridibundus, that occupy a wide variety of habitats within and beside intertidal mudflats. We investigated to what degree black-headed gulls (1) use intertidal mudflats versus terrestrial habitats during different phases of the tidal cycle, (2) follow the tidal wave to exploit recently exposed mudflats and (3) whether these behaviours are influenced by central place foraging. For this, 11 black-headed gulls breeding on the Wadden Sea island Griend were tracked during two years using GPS loggers. When commuting to and from Griend, up to 75% of their time was spent in intertidal areas during low and incoming tide, which increased to 92% when not behaving as central place foragers. While their movements were strongly linked to the tidal cycle, they did not follow the tidal wave across the tidal basin during either period. Rather, individuals foraged either predominantly west or east of Griend during low and incoming tide and mostly remained visiting these areas when not behaving as central place foragers. As one of the most abundant species in the Wadden Sea, the extensive use of intertidal mudflats highlights the importance of black-headed gulls within the intertidal food web of the Wadden Sea.

Genetic variation at innate and adaptive immune genes - contrasting patterns of differentiation and local adaptation in a wild gull.

Immunogenetic variation in natural vertebrate populations is expected to respond to spatial and temporal fluctuations in pathogen assemblages. While spatial heterogeneity in pathogen-driven selection enhances local immunogenetic adaptations and population divergence, different immune genes may yield contrasting responses to the environment. Here, we investigated population differentiation at the key pathogen recognition genes of the innate and adaptive immune system in a colonial bird species, the black-headed gull Chroicocephalus ridibundus. We assessed genetic variation at three toll-like receptor (TLR) genes (innate immunity) and the major histocompatibility complex (MHC) class I and II genes (adaptive immunity) in gulls from seven colonies scattered across Poland. As expected, we found much greater polymorphism at the MHC than TLRs. Population differentiation at the MHC class II, but not MHC-I, was significantly stronger than at neutral microsatellite loci, suggesting local adaptation. This could reflect spatial variation in the composition of extracellular parasite communities (e.g., helminths), possibly driven by sharp differences in habitat structure between colonies. Despite contrasting patterns of population differentiation, both MHC classes showed similar regimes of diversifying selection. Some significant population differentiation was also observed at TLRs, suggesting that innate immune receptors may respond to fine-scale spatial variation in pathogen pressure, although this pattern could have been enhanced by drift. Our results suggested that local adaptation at the pathogen recognition immune genes can be maintained at relatively small or moderate spatial scales in species with high dispersal potential and they highlighted the complexity of immunogenetic responses of animals to heterogeneous environments.

Sex- and age-dependent breeding plumage acquisition in monomorphic species, the Black-headed Gull Chroicocephalus ridibundus

In monomorphic species, like in the Black-headed Gull, both sexes look alike in breeding plumage. With large sets of data on captured and photographed birds and using the Underhill–Zucchini moult model, we provided a detailed pattern of breeding plumage development in this species by age and sex. This study, similar to other studies, documented first adults with the initial stage of head moult at the beginning of January, yet the mean start date of nuptial moult in adults was the end of February. Half of adults acquired full breeding plumage about mid-March and almost all of them before mid-April. The start date of nuptial moult was more variable in immatures. The mean start of head moult in immatures was 19th April, which is 52 days later than in adults, and the majority, i.e., 70%, did not complete moult until the end of May. We showed for the first-time sex-dependent breeding plumage acquisition in monomorphic species. According to the Underhill–Zucchini moult model, males started to moult on average 7 days earlier than females and their moult lasted 7 days longer. Hence, the final date of completed head moult was the same in both sexes. A fully developed hood is an important part of the status signalling during pairing; therefore, completing the moult before mating is important for both sexes.

Factors Affecting Colony Size and Breeding Parameters of Eared Grebe (Podiceps nigricollis) in Carp Ponds

Understanding important factors for breeding Eared Grebes (Podiceps nigricollis) is essential for its conservation. We aimed to study the impact of some factors on nests and breeding success in this species in fishponds (S Poland). Number of Eared Grebe nests were counted on particular carp ponds. Pond size, vegetation cover, number of nests in colonies of associated gull or tern species, and age of stocked common carp (Cyprinus carpio) were determined for all ponds with nests. We also investigated the relationship between nest size, material used to construct them and clutch size. Number of Eared Grebe nests positively correlated with number of breeding pairs of associated colonial species (terns or gulls). Selection of the breeding site by the Eared Grebe can be explained by appropriate nest protection by large colonies of associated species (Whiskered Tern Chlidonias hybrida and Black-headed Gull Chroicocephalus ridibundus). Nest size was not related to clutch size. A negative relationship between breeding success and number of nests of Eared Grebe was found. Food is a not limiting factor for the Eared Grebe on fishponds with extensive production, and presumably other factors such as weather conditions may explain the low breeding success of this species.

Occurrence of rats and their impacts on colonial waterbirds in a Danish fjord

Human development around the globe has led to great expansion of the Brown Rat (Rattus norvegicus), which has implications for local wildlife and especially ground-breeding birds. In this study, we analyse the colonisation and persistence of rats on small islets important to breeding waterbirds in a Danish fjord, and investigate the effect of rat presence on the number of breeding pairs of eight waterbird species. The islets had an annual rat colonisation probability of 6% and an annual rat population persistence rate of 65% (equalling an annual population survival rate of 62% when adjusting for re-colonisations upon extinctions). Contrary to our hypotheses, rat colonisation and persistence was uncorrelated with islet size, distance from the mainland and the presence of shrub cover. Rat presence had a significant negative effect on the number of breeding pairs of four waterbird species, including Avocet (Recurvirostra avosetta, reduced to 30% compared to years without rats), Black-headed Gull (Chroicocephalus ridibundus, reduced to 45%) and Common Tern (Sterna hirundo, reduced to 52%). The smaller bird species in particular seemed to be affected by the presence of rats, and control efforts aimed at reducing rat presence on important breeding bird islets may consequently have a positive effect on the occurrence and breeding success of these species. We found no evidence of birds acting on a memory of where rats had been present in the previous year, and further research is needed to investigate the precise mechanisms behind the recorded negative effects in the contemporary year, i.e. how do prospecting as well as settled breeders detect and behaviourally respond to the presence of rats.

Evidence of Nocturnal Migration over Sea and Sex-Specific Migration Distance of Dutch Black-Headed Gulls

Avian migration is recorded over long distances, but some species winter much closer to their breeding sites or do not migrate at all. Specifically, the family of gulls Laridae shows great within and among species variation in migration. However, the migration ecology of many gull species is still unknown, even for abundant and widespread species such as the Black-headed Gull Chroicocephalus ridibundus. Here, we aimed to map the migration of Black-headed Gulls using GPS-tracking data from eight birds from a declining colony at Griend in the Dutch Wadden Sea to study migration routes and timing as well as wintering habitat of these birds. Furthermore, we used this GPS-data and 199 colour-ring resightings of adult birds from the same colony to study their wintering locations and habitat. The GPS-tagged birds migrated away from the Dutch Wadden Sea between mid-September and late November. All migrated in western to south-western directions to wintering areas at 130 to 560 km from the breeding colony. The GPS-tagged individuals wintered in The Netherlands, France and the United Kingdom and migrated towards these wintering sites both diurnally and nocturnally. The data indicate that most movements over the North Sea were nocturnal, whereas most migratory movements over land were during the day. Colour-ring data showed that females wintered significantly further away than males. We found no indications for differences in timing of migration between males and females and also no sex-specific preference for nocturnal or diurnal migration. We argue that the hitherto undocumented prevalence of nocturnal sea crossings calls for a better assessment of the potential risks of offshore wind energy developments in the North Sea. As such, this and new GPS-tracking data of Black-headed Gulls can aid in the conservation of this common and widespread species by providing novel insights in migration behaviour and the connectivity between breeding and wintering grounds.

Gulls of a feather do not sleep whenever\u2014circadian rhythm of activity of black-headed gulls Chroicocephalus ridibundus during the incubation period

Many vertebrates exhibit a diel activity, steered by light–dark cycle. However, some colonial waterbirds, in that several species of gulls, are active not only in day hours but also at night. In this study, we aimed to investigate 24 h cycle of black-headed gulls (BHG) Chroicocephalus ridibundus activity with focus on sleep behaviour. We expected that 24 h patterns of activity differ between colonies located in various habitats, and within a colony between nests located in the centre vs at the edge. We studied behaviour based on 9600 of 30 s videos from camera-traps taken in six colonies and data from 10 GPS-tracked individuals from one colony recorded during incubation. BHGs stayed active on average during 48.1% of a night, mainly spent on passive and active nest defence, and on nest maintenance. BHGs spent similar time on these activities in day hours. Individuals breeding in the colony centre slept at night longer than those at its edge. BHGs stayed active during on average 76.5% of daytime. In two urban colonies with the highest nest densities and highest level of light pollution birds slept less during the day than in other studied colonies (three rural and one urban) characterized by lower densities and light intensity after sunset near the colony. Knowledge of nocturnal behaviour is crucial to comprehend 24 h activity patterns of an organism, especially to understand flexibility of behaviour crucial for restoration, like sleep.

Nearest-neighbour distance, rather than group size, affects vigilance in urban flocks of preening Black-headed Gulls Chroicocephalus ridibundus

ABSTRACT Capsule The total flock size and number of nearby neighbours did not affect vigilance behaviour in the Black-headed Gull Chroicocephalus ridibundus, but an increase in the nearest neighbour distance had a positive effect on measures of vigilance. Aims Vigilance allows animals to detect environmental stimuli, such as the presence of predators or competitors. Vigilance entails costs, however, because individuals may devote less time to other biologically important activities. We examined the trade-off between preening and vigilance in wintering Black-headed Gulls, while simultaneously considering the role of several confounding variables. Methods Using multivariate regression models we examined the effect of several predictors on three common measures of vigilance: scan frequency, average scan duration, and the percentage of time allocated to scanning. Results We did not detect a group-size effect on vigilance, but an increase in the nearest-neighbour distance had a positive effect on scanning frequency and the proportion of time focal gulls allocated to scanning. In addition, individuals at the periphery of flocks scanned their environment more frequently compared to centrally positioned gulls. Other variables that had significant effects on vigilance were location of roosting flocks, ambient temperature and wind speed. Conclusions In general, this study indicates that antipredator vigilance played an important role in overall vigilance in preening gulls in an urban environment.

A vagrant Black-headed Gull (Chroicocephalus ridibundus) documented from Saint Peter and Saint Paul Archipelago: Brazil’s first record

A vagrant Black-headed Gull (Chroicocephalus ridibundus) documented from Saint Peter and Saint Paul Archipelago: Brazil’s first record

Recent changes in breeding abundance and distribution of the Common Pochard (Aythya ferina) in its eastern range

BackgroundThe Common Pochard (Aythya ferina) (hereafter Pochard), a widespread and common freshwater diving duck in the Palearctic, was reclassified in 2015 from Least Concern to Vulnerable IUCN status based on rapid declines throughout its range. Analysis of its status, distribution and the potential causes for the decline in Europe has been undertaken, but there has never been a review of its status in the major part of its breeding range across Russia to the Pacific coast.MethodsWe reviewed the scientific literature and unpublished reports, and canvassed expert opinion throughout Russia to assess available knowledge about changes in the species distribution and abundance since the 1980s.ResultsWhile accepting available information may not be representative throughout the entire eastern range of the species, the review found marked declines in Pochard breeding abundance in the last two decades throughout European Russia. Pochard have also declined throughout Siberia. Declines throughout the steppe region seemed related to local drought severity in recent years, necessitating further research to confirm this climate link at larger spatial scales. Declines in the forest and forest-steppe regions appeared related to the major abandonment of fish farms in western Russia that had formerly provided habitat for breeding Pochard. However, hyper-eutrophication of shallow eutrophic lakes, cessation of grazing and haymaking in floodplain systems necessary to maintain suitable nesting habitat and disappearance of colonies of the Black-headed Gull (Chroicocephalus ridibundus) in a number of wetlands were also implicated. Increasing invasive alien predator species (e.g. American Mink Neovison vison and Raccoon Dog Nyctereutes procyonoides) and increasing spring hunting were also thought to contribute to declines. Reports of expansion in numbers and range only came from small numbers occurring in the Russian Far East, including on the border with China and the long-established isolated population on Kamchatka Peninsula.ConclusionsWidespread declines throughout the eastern breeding range of the Pochard give continued cause for concern. Although we could address all the potential causal factors identified above by management interventions, we urgently need better information relating to key factors affecting site-specific Pochard breeding success and abundance, to be able to implement effective actions to restore the species to more favourable conservation status throughout its breeding range.

Ravens respond to unfamiliar corvid alarm calls

Eavesdropping on heterospecific alarm calls is a crucial source of information for many species (including corvids) and it is effective especially if these species form mixed-species flocks, have a similar spectrum of predators, and share habitat. Previous research on wild common ravens (Corvus corax) has shown that they react to the jackdaws’ alarm call. We tested their responses to the heterospecific alarm calls of various bird species differing in familiarity and taxonomical relatedness to ravens. Two other corvid species (the blue jay Cyanocitta cristata and the European jay Garrulus glandarius) and two non-corvids (the black-headed gull Chroicocephalus ridibundus and the laughing gull Leucophaeus atricilla) were presented. We played back the tested alarm calls to free-ranging ravens at a feeding site and observed the ravens’ responses to particular stimuli. We observed three behavioural responses made by the tested ravens: flying away, freezing (ceasing to move and crouching on the ground), and vigilance (observing the surroundings). The ravens responded to the Eurasian jay alarm call by freezing and flying away and to the blue jay alarm call by freezing and vigilance. The laughing gull alarm call induced mostly vigilance and the black-headed gull alarm call did not elicit any reaction. The responses to the alarm calls of both jays were similar to the responses to the playbacks of conspecific alarm calls, used as control (as well as to the response to a jackdaw alarm call from the previous study), which may point to the existence of a specific corvid characteristic in their alarm calls. The response to the alarm calls of both American species included vigilance, which suggests an uncertainty about the meaning of the call.

Individuality in Egg Colouration of Black-Headed Gulls Chroicocephalus ridibundus across the Years Confirmed through DNA Analyses

The eggshell colouration among and within certain bird species is highly variable. Although many studies have addressed this variation, the reasons for it remain largely unclear. Consistent individual differences in egg colouration may improve the ability of colonially breeding birds to recognise their clutch among other neighbouring nests. Moreover, in species with a high incidence of intraspecific brood parasitism, such as the Black-head Gull Chroicocephalus ridibundus, egg colouration patterns may allow parents to expel foreign eggs from their own clutch. Here, we used standardised photography and image processing, including UV spectral information, to investigate egg colour patterns in female Black-headed Gulls (476 eggs in 170 clutches) during four breeding seasons, from 2015 to 2018 in NE Germany. We confirmed maternity by comparing DNA extracted from eggshells with feathers from the breeding female. Our results showed a greater similarity of eggs within a clutch than among clutches (ANOSIM: R = 0.43, P = 0.001). Black-headed Gulls showed consistent individual-specific eggshell colour pattern across consecutive breeding seasons. Genetic analyses further revealed one foreign egg was present in three out of 25 clutches (12%), but these eggs were not expelled by the gulls, possibly because these eggs did not differ significantly in colouration from their own. Additionally, we conducted a clutch exchange experiment to assess the reaction of the breeding pair to a foreign clutch. After 21 neighbouring clutches had been exchanged, adults came back immediately and incubated the interchanged clutch without any negative reaction. It seems that they do not use the specific colour pattern for recognition of their clutches, but possibly use other cues that remain to be investigated. While the function of individual egg colour patterns remains unclear, our results strongly suggest colour variation is driven by internal rather than external factors in this colonially breeding species.

Relaxation of selective constraints shapes variation of toll-like receptors in a colonial waterbird, the black-headed gull

Nonspecific innate immune response is activated by toll-like receptors (TLRs), which recognize conserved molecular motifs characteristic for a broad spectrum of pathogens. In this study, we examined nucleotide substitution patterns and allelic diversity at five TLR genes in a wild nonpasserine bird, the black-headed gull Chroicocephalus ridibundus. We hypothesized that balancing selection can maintain high allelic diversity of TLR genes in the black-headed gull because of its ecological characteristics, coloniality, and migratoriness, which are associated with increased exposure and transmission of pathogens. Although we found moderately high levels of sequence polymorphism (8–49 haplotypes retrieved per locus within a sample of 60 individuals), most of these haplotypes were recorded at low frequencies within our study population. At the same time, we found no convincing evidence for the role of balancing selection in the maintenance of this variation (Tajima’s D < 0.5), and sites with a significant excess of nonsynonymous mutations (dN/dS > 1) were recorded only at two loci (TLR5 and TLR7). This pattern is consistent with relaxation of selective constraints, where most mutations are slightly deleterious and usually removed by purifying selection. No differences in the diversity and nucleotide substitution rates were found between endosomal loci responsible for viral RNA sensing and loci responsible for the recognition of extracellular pathogens. Our study provides the first information on evolutionary mechanisms shaping polymorphism of TLRs in a species from Lari suborder (gulls and allies) and suggests that TLR genes may be poorly responsive to ecological and life-history characteristics of hosts.

Preen oil chemical composition in herring gull Larus argentatus, common gull Larus canus and black-headed gull Chroicocephalus ridibundus confirms their status as two separate genera

Fatty acid and alcohol components of preen oil were determined in three gull species that belong to two systematic genera: herring gull Larus argentatus, common gull Larus canus and black-headed gull Chroicocephalus ridibundus. All gulls were captured in winter, in Gdańsk, Poland. All gulls produced monoesters composed of C7–C16 saturated fatty acids and C11–C20 saturated alcohols, with n-octanoic acid and n-hexadecanol as the major fatty acid and alcohol, respectively. Preen oils of black-headed gull had higher content of trimethyl fatty acids, 2,8-dimethylundecanoic acid, 2,6-dimethylundecanoic acid and 2,6-dimethylnonanoic acid, and lower content of 2-methyl fatty acids than oils of herring gull and common gull. Preen oils produced by black-headed gull also had lower content of 2-methyl alcohols. The relative contents of n-octanoic acid and n-hexadecanol did not differ among species. The differences among species are probably not a result of different diet, as all gulls fed mainly on household refuse. Hence, preen oil analysis confirmed the taxonomic relations among these gull species, that recently were placed into two different genera.

Melanin-based plumage ornamentation signals condition and physiological stress in the Black-headed Gull

There is increasing evidence that melanin-based plumage ornaments play a role in the sexual selection of birds, although there seems to be little consensus on the mechanisms underlying the signalling function of melanin-based plumage. The aim of this study was to assess the potential of a melanin-based plumage ornament (brown hood) to reflect components of individual quality (condition and physiological stress) in a common larid species, the Black-headed Gull Chroicocephalus ridibundus. For this purpose, we measured the size of the hood in over 500 Black-headed Gulls captured in several breeding colonies distributed across Poland. We found that hood size correlated positively with blood haemoglobin concentration, although we found no evidence for a relationship with blood glucose concentration or body mass. There was also a negative relationship between hood size and physiological stress, as assessed by leucocyte profiles (heterophil/lymphocyte ratio). We found this correlation in both sexes, suggesting that hood size may be an honest signal of individual quality in males and females, which implies a mutual mate choice in the Black-headed Gull. Finally, the relationship between hood size and blood haemoglobin concentration was primarily attributed to the parallel variation of these traits among the colonies, suggesting that Black-headed Gulls may settle in colonies in a despotic manner. As far as we are aware, our study is one of the first to show an honest signalling role of melanin-based ornaments in the gull family, Laridae. It remains to be tested whether different melanin-based plumage ornaments in gulls are developmentally and functionally integrated with each other and with carotenoid-based integument coloration.

Black-headed gulls (Chroicocephalus ridibundus) - a natural reservoir of potentially pathogenic microfungi?

Mycological studies of selected populations of black-headed gulls were carried out in response to the increasing interest in wild birds as reservoirs of potentially pathogenic fungi and links in the epidemiological chain of mycoses hazardous to human and animals. The biological material comprised swabs from the beaks and cloacae of adult and young birds subjected to standard mycological diagnostics. 79.5% of samples were positive, comprising 22 fungal species belonging to 10 genera, mainly Candida, Rhodotorula, Aspergillus, Fusarium, Cryptococcus, and Trichosporon. The most frequently isolated species were Candida albicans and Rhodotorula rubra, found in the beaks of females and young birds and in the cloacae of young birds with comparable frequency. Cryptococcus laurentii, Cr. neoformans, Aspergillus niger, A. flavus, and Rh. muscilaginosa were isolated relatively frequently from all birds. The results highlight the ecological importance of wild birds in the circulation of potentially pathogenic fungi in the biosphere.