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Golden Eagles Aquila chrysaetos colonized the northern California Channel Islands, an archipelago located off the coast of southern California, USA, in the early 1990s, owing in part to the presence of Feral Pigs Sus scrofa. Eagles preyed on piglets and on the endemic Island Fox Urocyon littoralis, driving three endemic subspecies of the Island Fox (U. l. santacruzae, U. l. santarosae and U. l. littoralis) toward extirpation. Using stable isotopes (δ¹³C and δ¹⁵N) measured from feathers and blood of Golden Eagles and from meat and bone of their prey, along with the proportion of prey consumed estimated from nest excavations as informative priors, we show that shifts in Eagle isotopic signatures tracked community reorganization: when pigs and foxes were abundant, Eagles consumed them in higher proportions than other prey; when foxes became scarce owing to Eagle predation, Eagle diet shifted toward pigs, but also diversified to include Common Ravens Corvus corax and seabirds (Larus spp. and Phalacrocorax spp.); and finally, after pigs were eradicated and 35 Golden Eagles had been captured and removed from Santa Cruz Island, a lone remaining pair of Eagles reversed their diet to include more foxes. Our findings reveal that shifts in stable isotope signatures from tissues of an apex predator can be used as a general proxy to monitor changes in the prey community; however, if sample sizes are small, informative priors are both essential and overwhelmingly influential, and changes in abundance of preferred prey may mask or fail to reveal changes in less preferred prey. Given that apex predators are at the top of trophic hierarchies, that they are often important drivers of community structure and that they sample prey continuously from their community, isotopic signatures of their tissues may be useful for monitoring community change.

Gulls (Larus spp.) have frequently been reported to carry Escherichia coli exhibiting antimicrobial resistance (AMR E. coli); however, the pathways governing the acquisition and dispersal of such bacteria are not well described. We equipped 17 landfill-foraging gulls with satellite transmitters and collected gull faecal samples longitudinally from four locations on the Kenai Peninsula, Alaska to assess: (a) gull attendance and transitions between sites, (b) spatiotemporal prevalence of faecally shed AMR E. coli, and (c) genomic relatedness of AMR E. coli isolates among sites. We also sampled Pacific salmon (Oncorhynchus spp.) harvested as part of personal-use dipnet fisheries at two sites to assess potential contamination with AMR E. coli. Among our study sites, marked gulls most commonly occupied the lower Kenai River (61% of site locations) followed by the Soldotna landfill (11%), lower Kasilof River (5%) and upper Kenai River (1%). Gulls primarily moved between the Soldotna landfill and the lower Kenai River (94% of transitions among sites), which were also the two locations with the highest prevalence of AMR E. coli. There was relatively high spatial and temporal variability in AMR E. coli prevalence in gull faeces and there was no evidence of contamination on salmon harvested in personal-use fisheries. We identified E. coli sequence types and AMR genes of clinical importance, with some isolates possessing genes associated with resistance to as many as eight antibiotic classes. Our findings suggest that gulls acquire AMR E. coli at habitats with anthropogenic inputs and subsequent movements may represent pathways through which AMR is dispersed.

Opportunist gulls use anthropogenic food subsidies, which can bolster populations, but negatively influence sensitive local ecosystems and areas of human settlement. In the eastern Gulf of Maine, Canada, breeding herring gulls Larus argentatus have access to resources from aquaculture, fisheries and mink farms, but the relative influence of industry on local gull populations is unknown. Our objectives were to 1) assess use of natural and anthropogenic habitats by herring gulls from multiple colonies, 2) evaluate variation among colonies in use of distinct resource types within these habitats and 3) highlight areas of high gull:industry interaction. Using GPS devices on 39 gulls from four colonies, we identified visitation behaviour (slow, localized movements) and assigned visits to nine resource types. To evaluate the spatial distribution of visits, we created a use intensity index, reflecting both fidelity (i.e. repeated visits) and time spent in specific areas. All four anthropogenic resource types were heavily used (56 ± 11% of visiting time across colonies), notably, fish plants and mink farms. Despite large distances among three colonies, birds overlapped at particular distant, inland mink farms. In contrast, birds from close colonies overlapped in visitation to specific nearby resources (e.g. fish plants and human settlement), and otherwise diverged in distribution and use of offshore and coastal areas. Birds from three colonies also made frequent, long visits to uninhabited islands. Industry is clearly influencing the behaviour of breeding gulls in the eastern Gulf of Maine, Canada, where birds are travelling great distances or spending large proportions of time interacting with anthropogenic resources, while otherwise paying lengthy visits to nearby coastal islands. Studies have shown that concentrations of gulls can have harmful direct and indirect ecological and societal impacts. Our findings have implications for the management and regulation of industry to mitigate detrimental effects on local ecosystems and humans.

Human impacts alter landscapes with consequences for the distribution and availability of high‐quality food resources to populations inhabiting those landscapes, which may impact on the reproductive output of individuals in those populations. The sensitivity of wild populations to changes in food resources may vary among stages of the annual cycle. For example, in birds, effects are likely to be greater during costly stages such as egg production. Here we compare assimilated diet (from stable isotope analysis of chick feathers) and egg traits (egg size, shape, eggshell colour and maculation, using pattern‐analysis software) in Herring Gulls Larus argentatus, across seven colonies in southwest Scotland and Northern Ireland. The Herring Gull is an opportunistic, generalist forager on both marine and terrestrial resources which frequently exploits anthropogenic food sources such as fishery discards and human refuse. We found that larger eggs were laid in colonies where females consumed either a higher proportion of marine resources or terrestrial resources; smaller eggs were laid in colonies where females had an intermediate diet. In colonies where females consumed more marine items, they also laid eggs with higher maculation (intensity and size of spots) compared with colonies where females mainly consumed terrestrial food. We also found smaller and more pointed eggs, suggestive of resource shortages, in larger colonies. Generalist foragers are often thought to have the capacity to buffer themselves against changes in the food web, provided that enough alternative food is available. However, this study highlights that specializing on the most profitable or available resources has consequences for egg traits even in an opportunistic generalist forager exploiting a large range of habitats. If variation in egg traits is related to reproductive output, then understanding the impact of assimilated diet on reproduction early in the breeding season can provide important insights into how populations will respond to landscapes altered by human impact.

Herring gulls (Larus argentatus) are opportunistic predators that prefer to forage in the intertidal zone, but an increasing degree of terrestrial foraging has recently been observed. We therefore aimed to analyze the factors influencing foraging behavior and diet composition in the German Wadden Sea. Gulls from three breeding colonies on islands at different distances from the mainland were equipped with GPS data loggers during the incubation seasons in 2012–2015. Logger data were analyzed for 37 individuals, including 1,115 foraging trips. Herring gulls breeding on the island furthest from the mainland had shorter trips (mean total distance = 12.3 km; mean maximum distance = 4.2 km) and preferred to feed on the tidal flats close to the colony, mainly feeding on common cockles (Cerastoderma edule) and shore crabs (Carcinus maenas). In contrast, herring gulls breeding close to the mainland carried out trips with a mean total distance of 26.7 km (mean maximum distance = 9.2 km). These gulls fed on the neobiotic razor clams (Ensis leei) in the intertidal zone, and a larger proportion of time was spent in distant terrestrial habitats on the mainland, feeding on earthworms. δ 13C and δ 15N values were higher at the colony furthest from the mainland and confirmed a geographical gradient in foraging strategy. Analyses of logger data, pellets, and stable isotopes revealed that herring gulls preferred to forage in intertidal habitats close to the breeding colony, but shifted to terrestrial habitats on the mainland as the tide rose and during the daytime. Reduced prey availability in the vicinity of the breeding colony might force herring gulls to switch to feed on razor clams in the intertidal zone or to use distant terrestrial habitats. Herring gulls may thus act as an indicator for the state of the intertidal system close to their breeding colony.

Environmental contaminants are found throughout Arctic marine ecosystems, and their presence in seabirds has been associated with toxicological responses. However, there are few studies of genotoxicity in Arctic avian wildlife. The purpose of the present study was to quantify deoxyribonucleic acid (DNA) damage in lymphocytes of selected seabird species and to examine whether accumulation of organohalogen contaminants (ΣOHCs) affects DNA damage. Blood was sampled from common eider (Somateria mollissima), black guillemot (Cepphus grylle), black-legged kittiwake (Rissa tridactyla), glaucous gull (Larus hyperboreus), arctic skua (Stercorarius parasiticus), and great skua (Stercorarius skua) in Kongsfjorden, Svalbard (Norway). Contaminant concentrations found in the 6 species differed, presumably because of foraging ecology and biomagnification. Despite large differences in contaminant concentrations, ranging from ΣOHCs 3.3 ng/g wet weight in the common eider to ΣOHCs 895 ng/g wet weight in the great skua, there was no strong difference among the species in baseline DNA damage or sensitivity to a genotoxic stressor (hydrogen peroxide). Baseline levels of DNA damage were low, with median values ranging from 1.7% in the common eider to 8.6% in the great skua. There were no associations between DNA damage and contaminants in the investigated species, suggesting that contaminant concentrations in Kongsfjorden are too low to evoke genotoxic effects, or possibly that lymphocytes are resistant to strand breakage. Clearly, genotoxicity is a topic for future studies of Arctic seabirds. Environ Toxicol Chem 2018;37:1084-1091. © 2017 SETAC.

International audience; Acquired carbapenemases currently pose one of the most worrying public health threats related to antimicrobial resistance. A NDM-1-producing Salmonella Corvallis was reported in 2013 in a wild raptor. Further research was needed to understand the role of wild birds in the transmission of bacteria resistant to carbapenems. Our aim was to investigate the presence of carbapenem-resistant Escherichia coli in gulls from southern France. In 2012, we collected 158 cloacal swabs samples from two gull species: yellow-legged gulls (Larus michahellis) that live in close contact with humans and slender-billed gulls (Chroicocephalus genei) that feed at sea. We molecularly compared the carbapenem-resistant bacteria we isolated through culture on selective media with the carbapenem-susceptible strains sampled from both gull species and from stool samples of humans hospitalized in the study area. The genes coding for carbapenemases were tested by multiplex PCR. We isolated 22 carbapenem-resistant E. coli strains from yellow-legged gulls while none were isolated from slender-billed gulls. All carbapenem-resistant isolates were positive for blaVIM-1 gene. VIM-1-producing E. coli were closely related to carbapenem-susceptible strains isolated from the two gull species but also to human strains. Our results are alarming enough to make it urgently necessary to determine the contamination source of the bacteria we identified. More generally, our work highlights the need to develop more bridges between studies focusing on wildlife and humans in order to improve our knowledge of resistant bacteria transmission routes.

Successful reproduction often depends upon parents providing offspring with resources and protection. In birds, reproductive success can often be enhanced by parents engaging in antipredator behaviors, but these behaviors can be costly. Theoretically, individuals should temporally modify the intensity of nest defense behavior to balance the costs and benefits of current and future reproductive success. More specifically, nest defense should vary throughout a nesting attempt to maximize fitness of the adults. Here, we consider the relationship between nest defense behavior and chick vulnerability in the herring gull (Larus argentatus), where chicks are under high predation risk. We estimated chick vulnerability by quantifying survival probabilities at different periods of the nestling stage. Simultaneously, we quantified changes in parental aggression throughout the nesting cycle by simulating predation attempts using a human predator model. We found that chick survival probabilities were lowest (i.e., vulnerability was highest) and parental aggression in nest defense was greatest during the first 10 days after hatching. Thus, we show that parents are most defensive when chicks are most vulnerable and that adults optimize nest defense behaviors in a way that maximizes their fitness.

Gulls (Larus spp.) commonly roost in large numbers on inland and coastal waters, yet there is little information on how or where gulls choose sites for roosting. Roost site selection can lead to water quality degradation or aviation hazards when roosts are formed on water supply reservoirs or are close to airports. Harassment programs are frequently initiated to move or relocate roosting gulls but often have mixed results because gulls are reluctant to leave or keep returning. As such, knowledge of gull roost site selection and roosting ecology has applied and ecological importance. We used satellite telemetry and an information-theoretic approach to model seasonal roost selection of ring-billed (L. delawarensis) and herring gulls (L. argentatus) in Massachusetts, USA. Our results indicated that ring-billed gulls preferred freshwater roosts and will use a variety of rivers, lakes, and reservoirs. Herring gulls regularly roosted on fresh water but used salt water roosts more often than ring-billed gulls and also roosted on a variety of land habitats. Roost modeling showed that herring and ring-billed gulls selected inland fresh water roosts based on size of the water body and proximity to their last daytime location; they selected the largest roost closest to where they ended the day. Management strategies to reduce or eliminate roosting gulls could identify and try to eliminate other habitat variables (e.g., close-by foraging sites) that are attracting gulls before attempting to relocate or redistribute (e.g., through hazing programs) roosting birds. © 2016 The Wildlife Society.

Studies of avian nest success often focus on examining influences of variation in environmental and seasonal factors. However, in-depth evaluations can also incorporate variation in individual incubation behaviour to further advance our understanding of avian reproductive ecology. We examined these relationships in colonially nesting Black-crowned Night-Herons Nycticorax nycticorax using intensive video-monitoring methods to quantify incubation behaviours. We modelled nest survival as a function of both extrinsic factors and incubation behaviours over a 3-year period (2010–12) on Alcatraz Island, USA. Model-averaged parameter estimates indicated that nest survival increased as a function of greater incubation constancy (% of time spent incubating eggs within a 24-h period), and average daily precipitation throughout the nesting stage. Common Ravens Corvus corax are the only known nest predator of Night-Herons on Alcatraz Island, as on many other coastal Pacific islands. We also investigated the effects of heterospecific nesting of California Gulls Larus californicus and Western Gulls Larus occidentalis in a mixed-species colony with Night-Herons, based on nesting proximity data collected over a 2-year period (2011–12). This second analysis indicated that, in addition to incubation behaviours, nesting heterospecifics are an important factor for explaining variation in Night-Heron nest survival. However, contrary to our original expectation, we found that Night-Herons experienced increased nest survival with increasing distance from gull colony boundaries. These results may apply to other areas with multiple colonial nesting species and similar predator communities and climatic patterns.

Parental incubation behavior largely influences nest survival, a critical demographic process in avian population dynamics, and behaviors vary across species with different life history breeding strategies. Although research has identified nest survival advantages of mixing colonies, behavioral mechanisms that might explain these effects is largely lacking. We examined parental incubation behavior using video-monitoring techniques on Alcatraz Island, California, of black-crowned night-heron Nycticorax nycticorax (hereinafter, night-heron) in a mixed-species colony with California gulls Larus californicus and western gulls L. occidentalis. We first quantified general nesting behaviors (i.e. incubation constancy, and nest attendance), and a suite of specific nesting behaviors (i.e. inactivity, vigilance, preening, and nest maintenance) with respect to six different daily time periods. We employed linear mixed effects models to investigate environmental and temporal factors as sources of variation in incubation constancy and nest attendance using 211 nest days across three nesting seasons (2010–2012). We found incubation constancy (percent of time on the eggs) and nest attendance (percent of time at the nest) were lower for nests that were located < 3 m from one or more gull nest, which indirectly supports the predator protection hypothesis, whereby heterospecifics provide protection allowing more time for foraging and other self-maintenance activities. To our knowledge, this is the first empirical evidence of the influence of one nesting species on the incubation behavior of another. We also identified distinct differences between incubation constancy and nest attentiveness, indicating that these biparental incubating species do not share similar energetic constraints as those that are observed for uniparental species. Additionally, we found that variation in incubation behavior was a function of temperature and precipitation, where the strength of these effects was dependent on the time of day. Overall, these findings strengthen our understanding of incubation behavior and nest ecology of a colonial-nesting species.

Predation by marine birds has resulted in substantial losses to runs of Pacific salmon Oncorhynchus spp., in some cases necessitating management action. Recovery of PIT tags on a seabird breeding colony (Ano Nuevo Island) indicated that western gulls Larus occidentalis prey upon federally listed Coho Salmon Oncorhynchus kisutch and steelhead O. mykiss in central California. Whereas salmonid populations in central California have decreased in recent decades, the western gull population on Ano Nuevo Island has increased. We observed gulls Larus spp. within estuaries to document predation and used radiotelemetry to examine gull movement in relation to the availability of salmonids. During 2008 and 2009, observed predation events of out-migrating salmonids by gulls were rare; 21 events occurred during 338 h of observations at two estuaries. During the prehatch and chick-rearing phases of breeding, which coincided with migration of salmonids from fresh to salt water, 74% of the detections of radio-tagg...

Kleptoparasitism involves the theft of resources such as food items from one individual by another. Such food-stealing behaviour can have important consequences for birds, in terms of individual fitness and population sizes. In order to understand avian host-kleptoparasite interactions, studies are needed which identify the factors which modulate the risk of kleptoparasitism. In temperate European intertidal areas, Eurasian oystercatchers (Haematopus ostralegus) feed primarily on bivalve molluscs, which may be stolen by kleptoparasitic species such as carrion crows (Corvus corone) and herring gulls (Larus argentatus). In this study we combined overwinter foraging observations of oystercatchers and their kleptoparasites on the Exe Estuary, UK, with statistical modelling to identify the factors that influence the likelihood of successful food stealing behaviour occurring. Across the winter, 16.4 % of oystercatcher foraging attempts ended in successful kleptoparasitism; the risk of theft was lowest in February (10.8 %) and highest in December (36.3 %). Using an information theoretic approach to compare multiple logistic regression models we present evidence that the outcome of host foraging attempts varied with the number of kleptoparasites per host within the foraging patch for two out of five individual months, and for all months grouped. Successful, kleptoparasitism was more likely to occur when the total number of all kleptoparasites per host was greater. Across the entire winter study period, oystercatcher foraging attempts that resulted in kleptoparasitism were associated with a mean number of kleptoparasites per host that was more than double that for foraging attempts that ended in the oystercatcher successfully consuming the mussel. Conversely, the stage of the tidal cycle within the estuary did not affect the outcome of oystercatcher foraging attempts. Our study provides evidence that bird numbers influence the risk of kleptoparasitism within avian assemblages.

Eggs of 3 seabird species, common eider (Somateria mollisima), European shag (Phalacrocorax aristotelis aristotelis), and European herring gull (Larus argentatus), were surveyed for a broad range of legacy and emerging pollutants to assess chemical mixture exposure profiles of seabirds from the Norwegian marine environment. In total, 201 chemical substances were targeted for analysis ranging from metals, organotin compounds, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and associated metabolites, chlorinated paraffins, chlorinated and nonchlorinated organic pesticides, per- and polyfluoroalkyl substances (PFAS), dechlorane plus, octachlorostyrene, brominated flame retardants (BFRs), organophosphorous compounds, brominated and alkyl phenols, cyclic siloxanes, and phthalates. Of the chemicals targeted, 149 substances were found above the detection limits, with metals dominating the contaminant profile and comprising 60% of the total contaminant load. Polychlorinated biphenyls, pesticides, organophosphorous compounds, and PFAS were the dominant contaminant classes of organic pollutants found within the seabird species, with the highest loads occurring in herring gulls, followed by shag, and common eider. New generation pollutants (e.g., PFAS, organophosphorous compounds, and alkylphenols) were detected at similar or higher concentrations than the legacy persistent organic pollutants (POPs). Time trends of reported concentrations of legacy POPs appear to have decreased in recent decades from the Norwegian coastal environment. Concentrations of detected pollutants do not appear to have a negative effect on seabird population development within the sampling area. Additional stress caused by pollutants, however, may affect seabird health more at the individual level. Environ Toxicol Chem 2015;34:1296–1308. © 2015 SETAC

Identifying differences in reproductive success rates of closely related and sympatrically breeding species can be useful for understanding limitations to population growth. We simultaneously examined the reproductive ecology of American avocets Recurvirostra americana and black-necked stilts Himantopus mexicanus using 1274 monitored nests and 240 radio-marked chicks in San Francisco Bay, California. Although there were 1.8 times more avocet nests than stilt nests, stilts nonetheless fledged 3.3 times more chicks. Greater production by stilts than avocets was the result of greater chick survival from hatching to fledging (avocet: 6%; stilt: 40%), and not because of differences in clutch size (avocet: 3.84; stilt: 3.77), nest survival (avocet: 44%; stilt: 35%), or egg hatching success (avocet: 90%; stilt: 92%). We reviewed the literature and confirmed that nest survival and hatching success are generally similar when avocets and stilts breed sympatrically. In addition to species, chick survival was strongly influenced by age, site, and year. In particular, daily survival rates increased rapidly with chick age, with 70% of mortalities occurring ≤ 1 week after hatch. California gulls Larus californicus caused 55% of avocet, but only 15% of stilt, chick deaths. Differential use of micro-habitats likely reduced stilt chick's vulnerability to gull predation, particularly during the first week after hatch, because stilts nested in vegetation 2.7 times more often than avocets and vegetation height was 65% taller at stilt nests compared with avocet nests. Our results demonstrate that two co-occurring and closely related species with similar life history strategies can differ markedly in reproductive success, and simultaneous studies of such species can identify differences that limit productivity.

Lake Huron, the third largest freshwater lake in the world, has become increasingly oligotrophic since the early 1990s and is also currently experiencing substantial changes in species abundances and diversity. We used long-term biomonitoring data to calculate whole-body energy densities for Lake Huron rainbow smelt (Osmerus mordax), lake trout (Salvelinus namaycush), and also for herring gull (Larus argentatus) eggs collected from 1989–2011. Significant temporal declines in energy densities were observed for all three species, and significant declines were found for lake trout size-at-age and herring gull egg sizes. For lake trout and herring gulls, these declines occurred during a period of reduced abundance of pelagic forage fish and increased inclusion of terrestrial food in diets of herring gulls. Declining energy density in rainbow smelt occurred concomitant with declining phytoplankton and zooplankton resources, the principal energy source for this species. Reduced production capacity in lower trophic levels appears to be affecting upper trophic levels of the Lake Huron food web, emphasizing the cascading effects of ecosystem change.

Gull populations can severely limit the productivity of waterbirds. Relocating gull colonies may reduce their effects on nearby breeding waterbirds, but there are few examples of this management strategy. We examined gull predation and survival of Forster's tern (Sterna forsteri) chicks before (2010) and after (2011) the managed relocation of the largest California gull (Larus californicus) colony (24,000 adults) in San Francisco Bay, California. Overall, survival of radio-marked Forster's tern chicks from hatching to fledging was 0.22 � 0.03 (meanSE), and daily survival rates increased with age. Gulls were the predominant predator of tern chicks, potentially causing 54% of chick deaths. Prior to the gull colony relocation, 56% of radio-marked and 20% of banded tern chicks from the nearest tern colony were recovered dead in the gull colony, compared to only 15% of radio-marked and 4% of banded chicks recovered dead from all other tern colonies. The managed relocation of the gull colony substantially increased tern chick survival (by 900%) in the nearby ( 3.8km) reference tern colony (0.29 � 0.10 in 2010 and 0.25 � 0.09 in 2011). Among 19 tern nesting islands, fledging success was higher when gull abundance was lower at nearby colonies and when gull colonies were farther from the tern colony. Our results indicate that the managed relocation ofgull colonies away from preferred nesting areas of sensitive waterbirds can improve local reproductive success, but this conservation strategy may shift gull predation pressure to other areas or species. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

In earlier studies, elevated concentrations of polychlorinated biphenyl (PCB) and p,p'-dichlorodiphenyldichloroethylene (DDE) were reported in double-crested cormorant (Phalacrocorax auritus) eggs and tree swallow (Tachycineta bicolor) eggs and nestlings collected from lower Green Bay (WI, USA) in 1994 and 1995 and black-crowned night-heron (Nycticorax nycticorax) eggs collected in 1991. Comparable samples collected in 2010 and 2011 indicated that concentrations of PCBs were 35%, 62%, 70%, and 88% lower than in the early 1990s in tree swallow eggs, tree swallow nestlings, double-crested cormorant eggs, and black-crowned night-heron eggs, respectively; concentrations of DDE were 47%, 43%, 51%, and 80% lower, respectively. These declines are consistent with regional contaminant trends in other species. Concentrations of PCBs were higher in herring gull (Larus argentatus) than in black-crowned night-heron eggs collected from Green Bay in 2010; PCB concentrations in double-crested cormorant and tree swallow eggs were intermediate. The estimated toxicity of the PCB mixture in eggs of the insectivorous tree swallow was the equal to or greater than toxicity in the 3 piscivorous bird species. A multivariate analysis indicated that the composition percentage of lower-numbered PCB congeners was greater in eggs of the insectivorous tree swallow than in eggs of the 3 piscivorous species nesting in Green Bay. Dioxin and furan concentrations and the toxicity of these chemicals were also higher in tree swallows than these other waterbird species nesting in Green Bay.

The hypothesis that anatomical or physiological factors can constrain the production of vocalizations is supported by an increasing number of examples from a range of taxa, where acoustic variation is related to sex, body-size or condition. In this study, we combine anatomical and acoustic investigations in herring gulls Larus argentatus to 1) identify co-variation between sex, body size and the dimensions of the vocal apparatus and 2) test the possible effect of this co-variation on interindividual variation in the acoustics of alarm calls. We found that the vocal apparatus was sexually dimorphic, with males having longer trachea and bigger vibratile membranes than females. We also identified a relationship between the head–bill length – a secondary sexual trait – and the length of the trachea in males only. However, we failed to identify corresponding sex- and body-size related variation in the acoustic components of alarm calls. We suggest that this absence of a relationship between anatomical and acoustic dimensions may reflect the lack of biomechanical constraints exerted during the production of alarm calls, and that such relationships are more likely to be expressed in this species’ sexual calls, whose production is characterised by more pronounced, ritualised postures that are more likely to highlight inter-individual size variation.

We studied the long-distance migration of Lesser Black-backed Gulls Larus fuscus fuscus breeding in northern Norway along their eastern flyway using geolocators in 2009 and 2010. The majority of birds wintered in lakes in East Africa and the southeast Mediterranean was the most important stopover area. Larus f. fuscus along the eastern flyway travelled at a net travel speed of 399 and 177 km/day during the autumn and spring migration, respectively, higher than published travel speeds for Dutch Larus fuscus migrating along the western flyway. The results suggest that the long-distance migratory Norwegian L. f. fuscus seek to minimize time spent in transit, whereas lower travel speed during northerly spring migration may reflect differences in wind patterns or food conditions between spring and autumn.

Previous studies have shown inexplicable declines in breeding waterbirds within western New York/New Jersey Harbor between 1996 and 2002 and elevated polychlorinated dibenzo-p-dioxins and polychlorinated biphenyls (PCBs) in double-crested cormorant (Phalacrocorax auritus) eggs. The present study assessed associations between immune function, prefledgling survival, and selected organochlorine compounds and metals in herring gulls (Larus argentatus) and black-crowned night herons (Nycticorax nycticorax) in lower New York Harbor during 2003. In pipping gull embryos, lymphoid cells were counted in the thymus and bursa of Fabricius (sites of T and B lymphocyte maturation, respectively). The phytohemagglutinin (PHA) skin response assessed T cell function in gull and heron chicks. Lymphocyte proliferation was measured in vitro in adult and prefledgling gulls. Reference data came from the Great Lakes and Bay of Fundy. Survival of prefledgling gulls was poor, with only 0.68 and 0.5 chicks per nest surviving to three and four weeks after hatch, respectively. Developing lymphoid cells were reduced 51% in the thymus and 42% in the bursa of gull embryos from New York Harbor. In vitro lymphocyte assays demonstrated reduced spontaneous proliferation, reduced T cell mitogen-induced proliferation, and increased B cell mitogen-induced proliferation in gull chicks from New York Harbor. The PHA skin response was suppressed 70 to 80% in gull and heron chicks. Strong negative correlations (r = –0.95 to –0.98) between the PHA response and dioxins and PCBs in gull livers was strong evidence suggesting that these chemicals contribute significantly to immunosuppression in New York Harbor waterbirds. Environ. Toxicol. Chem. 2013;32:548–561. © 2012 SETAC

Breeding success of many Arctic‐breeding bird populations varies with lemming cycles due to prey switching behavior of generalist predators. Several bird species breed on islands to escape from generalist predators like Arctic fox Vulpes lagopus, but little is known about how these species interact. We studied brent geese Branta bernicla bernicla that share islands with gulls (Larus spec.) in Taimyr, Siberia (Russia). On one hand, gulls are egg predators, which occasionally steal an egg when incubating geese leave the nest for foraging bouts. On the other hand, gulls import marine resources to the islands, enriching the soil with their guano. We considered three hypotheses regarding clutch size of brent geese after partial nest predation. According to the “predator proximity hypothesis”, clutch size is expected to be smallest close to gulls, because of enhanced predator exposure. Conversely, clutch size is expected to be largest close to gulls, because of the supposedly better feeding conditions close to gulls, which might reduce nest recess times of geese and hence egg predation risk (“guano hypothesis”). Furthermore, gulls may defend their nesting territory, and thus nearby goose nests might benefit from this protection against other gulls (“nest association hypothesis”). We mapped goose and gull nests toward the end of the goose incubation period. In accordance with the latter two hypotheses, goose clutch size decreased with distance to the nearest gull nest in all but the lemming peak year. In the lemming peak year, clutch size was consistently high, indicating that partial nest predation was nearly absent. By mapping food quantity and quality, we found that nitrogen availability was indeed higher closer to gull nests, reflecting guanofication. Unlike predicted by the nest association hypothesis, a predation pressure experiment revealed that egg predation rate decreased with distance to the focal gull nests. We therefore propose that higher food availability close to gulls enables female geese to reduce nest recess time, limiting egg predation by gulls.

We recovered passive integrated transponder (PIT) tags from nine piscivorous waterbird colonies in the Columbia River basin to evaluate avian predation on Endangered Species Act (ESA)-listed salmonid Oncorhynchus spp. populations during 2007–2010. Avian predation rates were calculated based on the percentage of PIT-tagged juvenile salmonids that were detected as passing hydroelectric dams and subsequently were consumed and deposited by birds on their nesting colonies. Caspian terns Hydroprogne caspia (hereafter, “terns”) and double-crested cormorants Phalacrocorax auritus (hereafter, “cormorants”) nesting on East Sand Island in the Columbia River estuary consumed the highest proportions of available PIT-tagged salmonids, with minimum predation rates ranging from 2.5% for Willamette River spring Chinook salmon O. tshawytscha to 16.0% for Snake River steelhead O. mykiss. Estimated predation rates by terns, cormorants, gulls of two species (California gull Larus californicus and ring-billed gull L. ...

Understanding how animals partition effort between vigilance for predators and other conflicting activities has been a mainstay of animal behaviour research. Classical theories implicitly assume that animals alternate between high and low vigilance states over short timescales, but that average effort invested in vigilance is constant over an extended bout of such alternations. However, one recent model suggests that vigilance should be adjusted dynamically to short-term changes in the perception of predation risk and would tend to decrease with time. Indeed, as time passes by without disturbances, perception of the need for vigilance should decrease and prey animals may allocate more time to competing activities. Here, we examined how the proportion of sleeping gulls (Larus spp.) in loafing groups changed over time. Sleeping gulls can only maintain low levels of vigilance against external threats (compared to alert individuals), and we predicted that the proportion of sleeping gulls at loafing sites should increase over time when no disturbances occur. Statistically significant changes in the proportion of sleeping gulls as a function of time occurred in the majority of sequences and an increase was observed significantly more often than predicted by chance alone. This temporal pattern cannot be caused by reduction in hunger levels because gulls are not feeding at loafing sites. The results indicate that vigilance can be adjusted dynamically in response to short-term temporal changes in the perception of predation risk.

We studied the influence of glacial oscillations on the genetic structure of seven species of white-headed gull that breed at high latitudes (Larus argentatus, L. canus, L. glaucescens, L. glaucoides, L. hyperboreus, L. schistisagus, and L. thayeri). We evaluated localities hypothesized as ice-free areas or glacial refugia in other Arctic vertebrates using molecular data from 11 microsatellite loci, mitochondrial DNA (mtDNA) control region, and six nuclear introns for 32 populations across the Holarctic. Moderate levels of genetic structure were observed for microsatellites (FST= 0.129), introns (ΦST= 0.185), and mtDNA control region (ΦST= 0.461), with among-group variation maximized when populations were grouped based on subspecific classification. Two haplotype and at least two allele groups were observed across all loci. However, no haplotype/allele group was composed solely of individuals of a single species, a pattern consistent with recent divergence. Furthermore, northernmost populations were not well differentiated and among-group variation was maximized when L. argentatus and L. hyberboreus populations were grouped by locality rather than species, indicating recent hybridization. Four populations are located in putative Pleistocene glacial refugia and had larger τ estimates than the other 28 populations. However, we were unable to substantiate these putative refugia using coalescent theory, as all populations had genetic signatures of stability based on mtDNA. The extent of haplotype and allele sharing among Arctic white-headed gull species is noteworthy. Studies of other Arctic taxa have generally revealed species-specific clusters as well as genetic structure within species, usually correlated with geography. Aspects of white-headed gull behavioral biology, such as colonization ability and propensity to hybridize, as well as their recent evolutionary history, have likely played a large role in the limited genetic structure observed.

The avian pineal is a directly photosensory organ taking part in the organization of the circadian and seasonal rhythms. It plays an important role in regulation of many behavior and physiological phenomena including migration. The aim of the study was to investigate morphology of the pineal organ in the common gull (Larus canus). The light and electron microscopic studies were performed on the pineals of juvenile birds living in natural conditions of the Baltic Sea coast, which have been untreatably injured during strong storms in autumn and qualified for euthanasia. The investigated pineals consisted of a wide, triangular, superficially localized distal part and a narrow, elongated proximal part, attached via the choroid plexus to the intercommissural region of the diencephalon. The accessory pineal tissue was localized caudally to the choroid plexus. Based on the histological criteria, the organ was classified as the solid-follicular type. Two types of cells of fotoreceptory line were distinguished: rudimentary-receptor pinealocytes and secretory pinealocytes. Both types of cells were characterized by unusual features, which have been not previously described in avian pinealocytes: the presence of paracrystalline structures in the basal processes and their endings, the storage of glycogen in the form of large accumulations and the arrangement of mitochondria in clusters. Further studies on other species of wild water birds dwelling in condition of cold seas are necessary to explain if the described features of pinealocytes are specific for genus Larus, family Laridae or a larger group of water birds living in similar environmental conditions.

Studies of migration have revealed multiple trade-offs with other life-history traits that may underlie observed variation in migratory properties among ages and sexes. To assess whether, and to what extent, body size and ⁄or sex-specific differences in competition for resources (e.g. breeding territories or winter food) may shape variation in migration distance and timing of arrival in ecologically and phylogenetically related species, we combined over 30 000 sightings of individually marked, sexually mature males and females of Herring Gulls Larus argentatus and Lesser Black-Backed Gulls Larus fuscus with biometric measurements and phenological observations at a mixed breeding colony. In L. argentatus, larger males migrated further from the breeding colony, whereas migration distance was independent of body size in adult females. In L. fuscus, no relationship between body size and migration distance was apparent in either sex. Mean arrival dates at the breeding colony did not vary with migration distances but differed between males and females of L. argentatus (but not L. fuscus). As allometry at least partly explains sexual segregation in migration behaviour in L. argentatus, but not in L. fuscus, we conclude that the effect of body size on sex-related migratory strategies may vary between closely related, sympatric species despite similar size dimorphism.

The migrations and winter distributions of most seabirds, particularly small pelagic species, remain poorly understood despite their potential as indicators of marine ecosystem health. Here we report the use of miniature archival light loggers (geolocators) to track the annual migration of Sabine’s Gull Larus sabini, a small (c. 200 g) Arctic-breeding larid. We describe their migratory routes and identify previously unknown staging sites in the Atlantic Ocean, as well as their main Atlantic wintering area in the southern hemisphere. Sabine’s Gulls breeding in northeast Greenland displayed an average annual migration of almost 32 000 km (n = 6), with the longest return journey spanning close to 39 000 km (not including local movements at staging sites or within the wintering area). On their southern migration, they spent an average of 45 days in the Bay of Biscay and Iberian Sea, off the coasts of France, Spain and Portugal. They all wintered in closeassociation with the cold waters of the Benguela Upwelling, spending an average of 152 days in that area. On their return north, Sabine’s Gulls staged off the west African coast (Morocco, Mauritania, Senegal), spending on average 19 days at this site. This leg of migration was particularly rapid, birds travelling an average of 813 km⁄ day, assisted by the prevailing winds. Sabine’s Gulls generally followed a similar path on their outbound and return migrations, and did not exhibit the broad figure-of-eight pattern (anti clockwise in the southern hemisphere and clockwise in the northern hemisphere) seen in other trans-equatorial seabirds in the Atlantic and Pacific oceans.

Summary 1. Long range transportation via ocean currents and air of various organochlorines (OCs) has resulted in their intrusion in the high Arctic marine food web. At the Spitsbergen archipelago, including Bear Island (Norway), bioaccumulation in top predators like glaucous gulls (Larus hyperboreus) is high, severely affecting their breeding performance and survival. 2. In the present study, we examined the sex ratio of glaucous gull offspring at hatching in relation to the OC blood levels of female parents. Glaucous gulls have male-biased size dimorphism and females under stress with high levels of OCs are expected to skew the sex ratio towards the less costly female offspring. 3. Our data strongly suggest that among females with low levels of OCs, mothers in good body condition had a hatching sex ratio skewed towards males while those in poor body condition had a skew towards female offspring. However, contrary to expectations, females with high levels of OCs had a strong skew in sex ratio toward male offspring and this was most apparent among females in poor body condition. 4. Hatching body masses of male chicks (controlled for egg size) were negatively related to OC blood level of female parents. There was no such relationship for female offspring. 5. We discuss the skew in hatching sex ratio experienced by OC contaminated glaucous gulls in light of three hypotheses. One is that OC pollutants may mimic hormones and influence the sex determining processes suggested to be under control of steroids. Another is that female transfer of OCs to eggs may increase female embryo mortality. A third hypothesis is that elevated levels of OCs could trigger increased parental investment (terminal investment) which may represent an abortive strategy for OC contaminated gulls, further aggravating the negative impact of OCs on gull population parameters.

Zusammenfassung Ubertragungsversuche mit Syngamus trachea auf zwolf Hausenten, Anas platyrhynchos domestica, durch orale Verabreichung reifer Syngamuseier verliefen negativ, ebenso auf sieben Haustauben, Columba livia domestica, drei Zwergblasganse, Anser erythropus, zwei Singschwane, Cygnus cygnus, und funf Teichhuhner, Gallinula chloropus. Die Hausgans, Anser anser domesticus, erwies sicht als empfanglich, ebenso die japanische Zwergwachtel, Coturnix coturnix japonica. In sechs Silbermowen, Larus argentatus, wurde Syngamus trachea geschlechtsreif, die Patenz betrug jedoch nur 2–9 Tage. In je einem von vier infizierten Sabelschnablern, Recurvirostra avosetta, acht Kiebitzen, Vanellus vanellus, und sieben Austernfischern, Haematopus ostralegus, wurde das 4. oder unreife 5. Stadium erreicht. Zur Geschlechtsreife entwickelte sich Syngamus trachea hier nicht. Die Untersuchungen wurden durch eine Beihilfe der Gesellschaft der Freunde der Tierarztlichen Hochschule ermoglicht. Bei der Durchfuhrung der Versuche wurden wir durch die Herren Fischer und Reinsch, Laboranten des Instituts, unterstutzt. Hierfur sagen wir unseren besten Dank. Summary The host specificity of Syngamus trachea (Strongyloidea, Nematoda) Attempts to transmit Syngamus trachea to nine domestic ducks (Anas platyrhynchos domestica) by oral administration of mature Syngamus eggs gave negative results, and the same occurred with seven domestic pigeons (Columba livia domestica), three lesser white-fronted geese (Anser erythropus), two whooper swans (Cygnus cygnus) and five moorhens (Gallinula chloropus). The domestic goose (Anser anser domesticus) proved to be susceptible, as also was the Japanese dwarf quail (Coturnix coturnix japonica). In six herring gulls (Larus argentatus) the Syngamus trachea became sexually mature but the patent period lasted only two to nine days. In one out of four infected avocets (Recurvirostra avosetta), eight lapwings (Vanellus vanellus) and seven oyster catchers (Haematopus ostralegus) the parasite reached the fourth or fifth immature stages. In none of these species did Syngamus trachea reach sexual maturity. Resume Sur la specificite de l'hote de Syngamus trachea (strongyloide, nematode) Des essais de transmission de Syngamus trachea sur neuf canards colvert domestiques (Anas platyrhynchos domestica), par administration orale d'oeufs de Syngamus a maturite, s'averent negatifs. Il en est de měme chez sept pigeons biset domestiques (Columba livia domestica), trois oies naines (Anser erythropus), deux cygnes sauvages «chanteurs» (Cygnus cygnus) et cinq poules d'eau (Gallinula chloropus). L'oie cendred domestique (Anser anser domesticus), de měme que la caille naine japonaise (Coturnix coturnix japonica), se sont revelees sensibles. Chez six goelands argentes (Larus argentatus), Syngamus trachea est parvenu a maturite sexuelle, avec une patence de 2–9 jours seulement. Sur quatre avocettes (Recurvirostra avosetta), huit vanneux huppes (Vanellus vanellus) et sept huitriers pies (Haematopus ostralegus) infectes, on trouve une fois par espece d'oiseau le 4eme ou le 5eme stade immature. Syngamus trachea n'a pas atteint dans ces cas la maturite sexuelle. Resumen Sobre la especificidad de anfitrion de Syngamus trachea (Estrongiloideos, Nematodos) Los ensayos de transmision con Syngamus trachea a nueve patos domesticos, Anas platyrhynchos domestica, mediante la administracion oral de huevos Syngamus maduros, resultaron negativos, igual que a siete palomas domesticas, Columba livia domestica, tres ansares caretos enanos, Anser erythropus, dos cisnes cantores, Cygnus cygnus, y cinco pollas de agua, Gallinula chloropus. El ganso domestico, Anser anser domesticus, resulto ser receptible, igual que la codorniz japonesa enana, Coturnix coturnix japonica. En seis gaviotas comunes, Larus argentatus, maduro Syngamus trachea sexualmente, pero la patencia solo duraba 2-9 dias. En cada vez una de cuatro avocetas infestadas, Recurvirostra avosetta, ocho ave frias, Vanellus vanellus, y siete ostreros, Haematopus ostralegus, se alcanzo el 4° estadio o el 5° inmaturo. Aqui no se desarrollo Syngamus trachea hasta adquirir la madurez sexual.

Observations on 24 focal nests revealed that, at the time when parental investment in feeding fledging chicks declined, chicks showed a marked increase in begging, particularly in larger broods, whilst parents became less responsive to begging. That chicks suffer a cost from early termination of investment is indicated by the fact that third-hatched chicks, who had attempted (unsuccessfully) to initiate more feeds, were absent from the territory first, rather than the more mature first- and second-hatched chicks. Taken together, these results and related inter- and intra-brood contrasts in behaviour are interpreted as offering support for Trivers' theory of parent-offspring conflict over the termination of investment.

and Summary How a Common Tern (Sterna hirundo) Colony Defends itself against Herring Gulls (Larus argentatus) The subject of this study is the anti-predator behaviour of a small common tern colony near a large herring gull colony on the island of Mellum, West Germany (Fig. 1). In 1980 the number of gulls crossing this tern colony increased during the terns' chick-stage (Fig. 4). Observed predation of tern chicks was independent of tide and time of day (3., Fig. 5). The frequency of tern reactions corresponded to the number of herring gull crossings (Fig. 5, Table 1). The terns' responses increased between morning and evening (Fig. 8). Tern up-flights and attacks increased absolutely and as a percentage, with the advance of the breeding season (Fig. 3, 4). They were positively correlated with the observed chick predation and the number of pairs with chicks, most markedly with chicks older than 5 days (Figs. 3, 4; Table 1). This increased defence was maintained by fewer pairs as, by then, many had lost their own broods (Fig. 4). As the breeding season progressed, herring gulls increasingly became the main cause of tern up-flights and the object of the attacks (Figs. 9–11). The up-flights of the whole colony, which occurred frequently and spontaneously during incubation, were observed only rarely after hatching and were almost exclusively a response to herring gulls (Figs. 10, 12). The lower herring gulls flew over the colony, the more frequently common terns flew up or attacked and the more individuals were involved in these responses (Figs. 6, 13, 14). During the breeding period, communal up-flights and attacks by terns increased as a percentage (Figs. 12, 13, 15–17). Group-attacks effected changes in the gulls' flying-routes more often than did individual attacks (Fig. 18). Despite the defence behaviour and its adaptation to the predation pressure, herring gulls often succeeded in robbing chicks. This is why the breeding success of the common tern was poor (< 0.4 chicks/nest). Possible reasons for this are discussed.

Few birds parasitize living tissue of other birds or mammals. At Golfo San Jose, Argentina, kelp gulls, Larus domincanus, fed on live southern right whale, Eubalaena australis, mothers, landing on their backs and pecking at peeling skin or gouging into the energy-rich hypodermal blubber layer. Most attacks occurred while mothers were resting at the surface in the central nursery area. The typical immediate reaction of mothers to gull attacks was to lower the mid-back and rapidly raise the head and tail stock. Less frequently mothers submerged quickly. After their initial response mothers traveled rapidly, usually underwater, or adopted resting postures that submerged the vulnerable midback area. Gulls attacked singly or in small groups and alternated between following a single pair of whales and attacking several pairs sequentially. The intensity of maternal responses to these attacks affects the energy budget of mothers and calves during a time when energy conservation is important. Subtle postural shifts to submerge the back require less energy than rapid, frantic fleeing. Since gulls feed on whales without causing fatal injury this relationship is termed parasitic.

and Summary 1. Tinbergen (1953) concluded that herring gulls can recognize their own young by the time they are 5 days old. 2. Berens von Rautenfeld (1978) demonstrated that cliff nesting herring gulls would accept alien chicks older than 5 days old but supported Tinbergen's findings concerning ground nesting herring gulls. 3. In three separate recent studies involving 119 pairs nesting on diverse flat terrains there was a total of 16 naturally arising adoptions by pairs whose own young varied between 6 and 35 days of age. 4. All adoptions were by both members of the pair and all adoptees were of comparable age to the adopters' brood. 5. Some of the adoptions were by argentatus of fuscus. 6. It is concluded that herring gulls are unable to recognize their own young until they are about 35 days old and that at present nesting densities on flat terrain this inability is maladaptive. Zusammenfassung 1 Tinbergen (1953) schlos, das Silbermowen ihre eigenen Kuken erkennen, nachdem sie 5 Tage alt sind. 2 Berens von Rautenfeld (1978) hat bewiesen, das Silbermowen in Hangkolonien fremde Kuken akzeptieren, die alter als 5 Tage sind; er unter-stutzte aber Tinbergens Folgerung hinsichtlich der Silbermowen in Bodenkolonien. 3 In drei verschiedenen, neu durchgefuhrten Untersuchungen mit 119 brutenden Paaren in verschiedenen flachen Kolonien gab es insgesamt 16 naturliche Adoptionen bei Paaren, deren eigene Kuken zwischen 6 und 35 Tage alt waren. 4 Stets adoptierten beide Elternvogel, und alle Adoptierten waren im Alter den eigenen Kuken vergleichbar. 5 In einigen Fallen wurde fuscus von argentatus adoptiert. 6 Es ist zu schliesen, das die Silbermowen ihre eigenen Kuken erst erkennen konnen, wenn sie etwa 35 Tage alt sind, und bei den gegenwartigen Nestdichten auf flachem Gelande ist dies nicht sehr angepast.

The protector-species hypothesis explains mixed-species coloniality on the basis of benefits individuals of a species may receive by nesting with another species, the 'protector' species, that responds aggressively to potential threats. The reactions of nesting individuals to both natural and model predators were observed to determine whether black skimmers (Rhynchops niger) gain an antipredator advantage by nesting with gull-billed terns (Sterna nilotica). Observations of natural predators were gathered from three mixed-species and three single-species (black skimmers) subcolonies. Natural predators most commonly encountered by the colonies were herring gulls (Larus argentatus), laughing gulls (Larus atricilla), and ruddy turnstones (Arenaria interpres). Gull-billed terns responded to the gulls, but not to the turnstones, in higher proportions than did black skimmers. Two decoys, a mink and a gull, were used to simulate predatory encounters, and a duck decoy was used as a control at two mixed-species and one single-species subcolonies. Gull-billed terns responded in significantly higher proportitons than did skimmers to all decoy treatments in the mixed-species subcolonies. Mobbing of both natural and model predators by the terns suggests that skimmers may gain a reproductive advantage by nesting with these terns. However, the response of black skimmers to both natural and simulated predators was independent of the presence of gull-billed terns in the colony, indicating that black skimmers may not pcrceive these objects as threats, or may react differently to predators than do gull-billed terns.

Nest site selection is a critical component of reproduction and has presumably evolved in relation to predation, local resources, and microclimate. We investigated nest-site choice by king eiders (Somateria spectabilis) on the coastal plain of northern Alaska, USA, 2003–2005. We hypothesized that nest-site selection is driven by predator avoidance and that a variety of strategies including concealment, seclusion, and conspecific or inter-specific nest defense might lead to improved nesting success. We systematically searched wetland basins for king eider nests and measured habitat and social variables at nests (n = 212) and random locations (n = 493). King eiders made use of both secluded and concealed breeding strategies; logistic regression models revealed that females selected nests close to water, on islands, and in areas with high willow (Salix spp.) cover but did not select sites near conspecific or glaucous gull (Larus hyperboreus) nests. The most effective nest-placement strategy may ...

Parental age, body condition, and food availability have been found to influence breeding parameters in seabirds, such as clutch size, number of chicks hatched and fledged, hatching, fledging, and reproductive success. In this paper we analyze the influence of parental age and body condition estimated by body mass, and food availability estimated from catch per unit effort (CPUE) statistics for Pacific sardine (Sardinops caeruleus) + northern anchovy (Engraulis mordax) by the local fishing fleet, on the breeding parameters of the Heermann's Gull (Larus heermanni; a vulnerable species according to Mexican federal law) nesting in Isla Rasa, Gulf of California, Mexico. Results are based on data from 1123 recaptures of known-age individuals, ranging from 4 to 13 years of age, during seven observation years between 1989 and 1997. Ages of mated male and female gulls were positively correlated. Breeding parameters showed their lowest values in 1992, an El Niño year in which the birds also showed significantly lower individual masses for both males and females, and in which the local CPUE of sardine + anchovies was lowest. All breeding parameters increased significantly with parental age and were highest at 10-12 years. No significant statistical interactions were found between food availability and parental age on the breeding parameters. Through a path analysis we found that there is a strong chained relationship between variables: food availability, which is strongly driven by oceanographic conditions, affects both the survival of eggs into hatchlings and the survival of hatchlings into fledglings. This external factor and parental age, a biological factor intrinsic to each nesting couple, explain 41% of the observed between-nest variation in fledgling success.

Summary 1Tissue fatty acid signatures (FAS) can complement traditional methods of studying seabird diets. Although plasma lipid FAS are known to indicate dietary changes qualitatively, here we test whether they can be used to determine the proportions of different dietary items in a quantitative manner. 2Captive herring gulls (Larus argentatus) were fed North Atlantic plaice Pleuronectes platessa (demersal species made available to wild seabirds by fisheries) and herring Clupea harengus (pelagic fish often found naturally in their diet) with different mixing ratios (0%, 10%, 20% and 50% herring). 3Major fatty acids did not indicate diet, but several minor components in plasma, for example, 14 : 0, 18 : 3n-3, 18 : 4n-3 and C20–22 monounsaturated fatty acids (MUFA), showed good correlations with diet composition. Different fatty acids were incorporated from diet into plasma lipids with different calibration coefficients. 4Together with dose-dependent but inefficient (low calibration coefficient) transfer of 22 : 1n-11 (a major fatty acid of herring) to the plasma FAS of the gulls, the percentages of potential chain shortening products of 22 : 1n-11, that is, 20 : 1n-11, 18 : 1n-11 and 16 : 1n-11 increased with increasing proportion of herring in the diet. Notably, the dietary supply of these fatty acids itself did not change. Thus the metabolic products of certain dietary fatty acids can reflect the amount of their dietary precursors in a quantitative way. 5Despite the fact that many major fatty acids in FAS of seabird plasma are greatly modified by endogenous metabolism, several minor components of FAS (in this experiment 14 : 0, branched chain 17 : 0, 18 : 1n-7, 18 : 3n-3, 18 : 4n-3, C20–22 MUFA with their chain shortening products, and 22 : 4n-6) that can be accurately and reliably quantified by gas chromatography, vary proportionally to diet composition, allowing their use for monitoring temporal and spatial differences in seabird diet.

King eider (Somateria spectabilis) populations have declined markedly in recent decades for unknown reasons. Nest survival is one component of recruitment, and a female's chance of reproductive success increases with her ability to choose an appropriate nesting strategy. We estimated variation in daily nest survival of king eiders at 2 sites, Teshekpuk and Kuparuk, Alaska, USA, 2002–2005. We evaluated both a priori and exploratory competing models of nest survival that considered importance of nest concealment, seclusion, and incubation constancy as strategies to avoid 2 primary egg predators, avian (Larus spp., Stercorarius spp., and Corvus corax) and fox (Alopex lagopus). We used generalized nonlinear techniques to examine factors affecting nest survival rates and information-theoretic approaches to select among competing models. Estimated nest survival, accounting for a nest visitation effect, varied considerably across sites and years (0.21–0.57); however, given our small sample size, much of...

SUMMARY Herring Gulls nesting on rooftops in South Shields and Sunderland were observed during 1974–76. These colonies, then around 200 pairs in each town, have expanded rapidly despite culls. Ringing results identified the Forth area as an important source of recruits, and also suggested that females are more likely to breed away from their natal area than males. It is clear from the high breeding success that these towns provide favourable alternatives to more typical breeding sites. The gulls in the towns nest at low densities, other than on flat roofs. Their breeding success, averaging 1.2–1.6 chicks per pair, was higher than that recorded at more typical colonies, and on structurally isolated rooftop sites was almost double that on flat roofs. This high success is attributed to the absence of cannibalism in these small colonies and the lack of territorial aggression at the structurally isolated sites.

Herring Gull Larus argentatus eggs from a study colony in the Baltic showed a slight but significant variation in egg size within the laying sequence. Last-laid eggs were only about 5% smaller by volume than first eggs. There was no significant difference in dry yolk weight or dry albumen weight, although possible differences were evident. The chicks had nearly equal hatching weights and equally long tarsi. There was no differential mortality in the third chick in the study colony, and there were no indications of egg-size-mediated mortality. The birds in the colony produced an average of 1.45 fledglings per pair. Compared with several other studied colonies, the difference in egg size within a clutch was low, and a comparison of colonies from northwestern Europe suggests that variance within the clutch is negatively correlated with fledging success, so that a large difference in size between first and last eggs is associated with low fledging success. We suggest that the size of the last egg in the clutch reflects the feeding potential in the environment and is mainly a nonadaptive response to poor feeding conditions during laying.

SUMMARY 1 In April 1960, the volume of migration over an inland area in Uppland, Middle-Sweden, was simultaneously recorded by radar and field observations. From the data obtained frequency curves were plotted for each day and compared. Correlation between the radar and field observation curves (considering the total field material as well as the separate species) was poor, and it is concluded that most of the radar echoes must have originated from birds flying at heights invisible from the ground, while most of the visible migration was too low (mostly below 650 feet) to be caught by the radar. 2 The directions of movement were much the same on all days, heading mainly E.N.E.-N.E., both on radar and in the field, but on the last day visible migration headed distinctly more to the north. 3 The mean speeds of the echoes varied between 43 and 70 m.p.h. (maximum 75 m.p.h.). Allowing for wind the still-air flight speeds were 35–52 m.p.h. on all days except the last day, when few were above 45 m.p.h. This suggests that mainly the same groups of species were participating in the invisible movements recorded by radar every day. 4 The high-flying visible migrants (650–1,650 feet) were mainly water-birds, which presumably formed at least part of the radar migration. This assumption is well supported by the recorded still-air speeds of the echoes. 5 On each day an appreciable return migration was noted in the field but scarcely at all by radar, the returning birds generally moving low against the wind. On a day of cold northerly wind later in the spring, however, a distinct return migration was seen on the radar during the first hours of darkness. 6 The commonest genera observed in field were Fringilla, Turdus, Corvus, Columba, Vanellus, Larus, and Numenius, in that order. On two days larger numbers of Lapwings and crows were recorded, but the total number of flocks recorded was unaltered. In such cases the increased numbers of birds will go unrecorded by radar.

SUMMARY Various aspects of the breeding of three gulls, Larus thayeri, glaucoides and hyperboreus, which nested in colonies both on cliff ledges and on level ground in the eastern Canadian Arctic, were compared with those of the ground-nesting L. argentatus and the cliff-nesting Rissa tridactyla. As the result of adaptation to cliff ledge nesting, many aspects of the breeding biology of R. tridactyla were strikingly different from those of the ground-nesting European L. argentatus, but the behaviour of L. thayeri, glaucoides and hyperboreus clearly spanned these differences. Cliff-nesting individuals of thayeri and glaucoides were most like Rissa; ground-nesting individuals of these species were most like argentatus. L. thayeri was more like Rissa than was glaucoides. With but few exceptions, both cliff- and ground-nesting individuals of hyperboreus were most like argentatus. The factors responsible for the intra-specific differences between cliff- and ground-nesters of thayeri and glaucoides are not clear. Limited gene exchange between cliff and ground colonies occurs. Because of physical features of the nest, first-laid eggs were more liable to fall from ledges than second or third eggs. L. thayeri and glaucoides have evolved separate mechanisms to cope with this problem. Egg shape was multimodal in thayeri and glaucoides. Long pyriform eggs were less liable to fall from ledges than eggs of other shapes. L. thayeri laid more long pyriform eggs as first eggs than did glaucoides. L. thayeri lost fewer eggs than did glaucoides, but glaucoides replaced all lost eggs while thayeri did not. Delayed follicular atresia provided glaucoides with insurance of egg replacement. In thayeri, accessory follicles were reabsorbed after the first egg was laid; in argentatus, after the second egg, and in glaucoides after the third egg. At the approach of a predator, it was advantageous for cliff-dwelling chicks to remain motionless but for ground-dwelling chicks to flee their nests and to hide. Among the cliff-nesters, the “freezing in place” reaction of chicks was best developed in thayeri, to a lesser extent in glaucoides, and least in hyperboreus. Among the ground-nesters, chicks of glaucoides and hyperboreus behaved like those of argentatus and fled their nests when disturbed, but chicks of thayeri froze like their cliff-dwelling siblings. Reciprocal transfers of eggs and chicks between cliff and ground colonies indicated that in argentatus, glaucoides and hyperboreus, the factors determining a chick's reaction to disturbance came into play between hatching and the eighth day. In thayeri, the reaction appeared to be effectively innate. Chicks of glaucoides showed a greater predisposition to this behaviour than chicks of argentatus after both had received identical experience on cliff ledges. In thayeri, stereotypy of the freezing reaction has probably been a factor limiting the colonisation of areas where cliffs are scarce but predators present. In argentatus, lack of perfection of this behaviour (compared to glaucoides and thayeri) has probably been a factor preventing argentatus from attaining cliff ledges. L. hyperboreus, although nowhere abundant, is a widespread species nesting on level ground and on cliff ledges but lacking the modifications observed in glaucoides and thayeri; this is due to its size and aggressiveness, the fact that it picks nest-sites before glaucoides and thayeri arrive in the colonies, and that on cliffs it chooses the largest and most level ledges.

SUMMARY The average numbers of Herring Gulls Larus argentatus present in a breeding colony on Walney Island, Cumbria, were found to vary with the tidal cycle but to remain effectively constant with time of day through the breeding season. An activity survey, based on 50 Herring Gulls observed at half-hourly intervals during March and April 1973, showed that sleep and rest varied inversely with each other with sleep increasing to 50 per cent at midday. After a peak in the proportion of gulls asleep four hours before low tide, sleeping progressively decreased until low tide; seemingly a result of resident gulls waking and remaining more alert as others left the colony in search of food. Preening was constant throughout the day and tide cycle. Other behaviours (mostly courtship and agonistic behaviour associated with territory defence) increased slightly during low tide and were more common early and late in the day. Night observations of the gulls' activities showed that there was a peak of sleeping between midnight and 02.00 hours. It is suggested that Herring Gulls have a bimodal diel sleep pattern.

Summary We examined the pattern of colony occupation and egg-laying in five colonies of Herring Gulls nesting in New Jersey, U.S.A. Colonies formed from epicentres located in sparse bushes. The number of epicentres related to the number of birds nesting in the colonies. Colonies of over 250 pairs had more than one epicentre, whereas those with under 250 pairs had only one epicentre. Epicentres were not always in the geographical centre of the colonies. New territory-hunting pairs filled in the epicentre areas, and then nested outside these areas. The egg-laying pattern followed the settling pattern, but was more synchronous than the settling pattern. There was greater synchrony of egg-laying within sub-areas of the colonies than in the colonies as a whole. Further, synchrony correlated with the number of nests in sub-areas.

Summary. Wild birds whose eggs ark used for food belong mainly to large species and to those nesting colonially; in general, the eggs of such birds are both accessible and palatable. Charadriiformes are the most important egg-birds-both as regards total annual crop and number of species utilized. Charadriiformes and Anseriformes together comprise 85 (or about 60 per cent) of the species which have more or less extensively been exploited during the present century. Procellariiformes and Sphenisciformes are also important. The various species are considered in relation to the estimated annual egg-crop and the chief localities of exploitation: in terms of yield, Sterna fuscata takes pride of place, with an estimated crop in excess of 1,000,000 eggs; while species for which the cropping rate may lie between 1,000,000 and 100,000 eggs include Sphsniscus demersus, Pufinus temirostris, Gallus gallus, Gallinula chloropur, Vanellus vanellus, Larus argentatus, L. ridibundus, Sterna paradisaea, Anoiis stolidus, Uria lumvia and U. aalge.