Predictable anthropogenic food subsidies,density‐dependence and socio‐economic factors influence breeding investment in a generalist seabird

Recent European policies on the ban of fishing discards and the closure of open‐air landfills are expected to reduce predictable and abundant food resources for generalist seabirds. In order to forecast the consequences of this reduction on seabird breeding investment it is important to understand whether diverse anthropogenic foraging resources act synergistically or not and whether their influence is mediated by density‐dependent mechanisms. To assess these effects at large spatio‐temporal scale, we measured mean egg volume as a proxy of breeding investment in ca 5000 three‐egg clutches of the yellow‐legged gull Larus michahellis from 20 colonies of the Western Mediterranean, located both along European and African coasts. In European gull colonies, egg volume increased with the availability of fishing discards and landfills in the vicinity of the colony. However, the landfill effect was weaker than the effect of fishing discards, probably due to the lower quality of waste as food for gulls. In contrast, none of the anthropogenic food subsidies influenced egg volume in African colonies, likely due to socio‐economic differences (i.e. a much lower availability and predictability of both discards and waste food. Finally, results showed that the positive association between fishing discards and open‐air landfills on egg volume was mediated by negative density‐dependent mechanisms probably related to an increase in competition for food.     

Predator–prey dynamics of bald eagles and glaucous‐winged gulls at Protection Island,Washington, USA

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Effects of anthropogenic food resources on yellow-legged gull colony size on Mediterranean islands

Yellow-legged gull Larus michahellis populations have been studied on three archipelagos consisting of 20 islands distributed along 80 km of the French Mediterranean coastline. Population changes were analyzed between 1920 and 2006. In the first decades following their settlement on these islands, the yellow-legged gull populations showed a continuous exponential growth in the three archipelagos, in agreement with an annual geometric growth rate λ above 1. The population growth ceased to fit this model during the 1980s for the older colonies (Riou and Hyères Islands archipelagos). Thus, we focused on population changes occurring during the period 1982–2000, a pivotal period for which we have both precise census and anthropogenic food resource data, in order to determine environmental factors influencing these population changes using multiple linear regression models. An average annual growth rate of colony size was 1.02 for the last two decades. The changes in landfill availability, the gull density in 1982, and the nesting area in 1982 explained 84.4% of variation in colony size changes between 1982 and 2000. The yellow-legged gull changes on the islands in the last two decades increased as availability in anthropogenic food resources increased near the colony (positive ΔK). As a consequence, given no reduction in landfill activity or in accessibility for gulls, we expect this region to sustain continuous species expansion in the future.     

Demographic impact of landfill closure on a resident opportunistic gull

The management of mixed municipal waste can have an impact on wildlife and ecosystems. Previous studies have investigated how opportunistic species like gulls can react very fast to new landfills; however, the impact of landfill closure on bird populations is less investigated. Yet, there is a need to understand how fast and to what extent, animal populations can be adapted to new scenarios where the waste will not be deposited in landfill sites anymore. The aim is to determine the influence of landfill closures on apparent survival of a resident Yellow-legged Gull (Larus michahellis) population, used as a model species showing short-distance foraging movements, and with a high dependence on local food subsidies. Complementarily, we built some basic population growth models in order to determine how potential changes in survival (before/after landfill closure) will impact on population growth rate. Using a data set of 4,437 Yellow-legged Gull chicks ringed in four colonies over a period of 13 years, we obtained evidence supporting that the apparent survival was affected by landfill closure, especially if the landfill was located within a buffer of 10 km around the colony. Landfill closure affected the survival of first-year gulls (with a mean decrease of ~ 0.5–0.36), but not of older birds. Consequently, we did not detect a remarkable effect of landfill closures on population growth rate, probably due to the lack of effect on adult survival rates except for one of the surveyed colonies, where we found an annual decline of 7%.     

VIM‐1 carbapenemase‐producing Escherichia coli in gulls from southern France

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 bla_VIM‐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.     

Balancing Energy Budget in a Central-Place Forager: Which Habitat to Select in a Heterogeneous Environment?

Foraging animals are influenced by the distribution of food resources and predation risk that both vary in space and time. These constraints likely shape trade-offs involving time, energy, nutrition, and predator avoidance leading to a sequence of locations visited by individuals. According to the marginal-value theorem (MVT), a central-place forager must either increase load size or energy content when foraging farther from their central place. Although such a decision rule has the potential to shape movement and habitat selection patterns, few studies have addressed the mechanisms underlying habitat use at the landscape scale. Our objective was therefore to determine how Ring-billed gulls (Larus delawarensis) select their foraging habitats while nesting in a colony located in a heterogeneous landscape. Based on locations obtained by fine-scale GPS tracking, we used resource selection functions (RSFs) and residence time analyses to identify habitats selected by gulls for foraging during the incubation and brood rearing periods. We then combined this information to gull survey data, feeding rates, stomach contents, and calorimetric analyses to assess potential trade-offs. Throughout the breeding season, gulls selected landfills and transhipment sites that provided higher mean energy intake than agricultural lands or riparian habitats. They used landfills located farther from the colony where no deterrence program had been implemented but avoided those located closer where deterrence measures took place. On the other hand, gulls selected intensively cultured lands located relatively close to the colony during incubation. The number of gulls was then greater in fields covered by bare soil and peaked during soil preparation and seed sowing, which greatly increase food availability. Breeding Ring-billed gulls thus select habitats according to both their foraging profitability and distance from their nest while accounting for predation risk. This supports the predictions of the MVT for central-place foraging over large spatial scales.     

Satellite tracking of gulls and genomic characterization of faecal bacteria reveals environmentally mediated acquisition and dispersal of antimicrobial‐resistant Escherichia coli on the Kenai Peninsula,Alaska

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.     

Ecology of Slaty-Backed Gull (<Emphasis Type="Italic">Larus schistisagus</Emphasis>) Breeding on Kronotskoe Lake,Kamchatka Peninsula

The slaty-backed gull population of Kronotskoe Lake has not been subjected to anthropogenic impact for many decades. The number and distribution of the breeding colonies of the slaty-backed gulls on the islands of this largest freshwater reservoir of the Kamchatka Peninsula are presented. Data on the breeding phenology, the seasonal dynamics of the food composition of breeding gulls, the foraging distance, and breeding success are considered. These data are compared to the results obtained earlier for Kuril’skoe Lake. Both gull populations are unique in that they are the only freshwater colonies within the distribution range of this marine species. The breeding success of the slaty-backed gulls on Kronotskoe Lake suffers from predation, both intra- and interspecific, in the latter case from brown bears and sea eagles. The hatching period and the fledging time of chicks in this population are both shifted to the end of summer, when gulls have the most abundant food available within the lake area, which increases successful survival of the fledglings. Despite considerable differences between the ecosystems of Kronotskoe Lake and Kuril’skoe Lake, there are several common features in the diets of the gull populations living on the lakes: (1) Despite the fact that gulls perform foraging flights to the sea coast, they only take fish and almost never collect marine invertebrates there. (2) Nearly half of all food items are taken within a 40-km distance from the colony. (3) During the growth period of chicks, gulls from both lakes rely on salmonids (anadromous in Kuril’skoe Lake, resident in Kronotskoe Lake) that they hunt in the lakes near their colonies.     

The decay of parasite community similarity in ring‐billed gulls Larus delawarensis and other hosts

The similarity of parasite communities often decays with increasing geographic distance. Here, geographic distance decay is evaluated in parasite communities of 145 ring‐billed gulls from six localities in Quebec, Canada, among both individual gulls and gull populations. Spatial decay in similarity is compared to temporal decay, using host age differences as a distance measure. The similarity of parasite communities of individual gulls from localities spanning 300 km within Quebec is more strongly associated with host age differences than with geographic distance. Among gull populations in Quebec, only geographic distance is significantly related to parasite community similarity. The explanatory power of geographic distance is higher still when data from Quebec are combined with those from a study conducted 3000 km away, indicating an effect of spatial scale on geographic distance decay. The rate at which parasite community similarity decays with distance in gulls is compared with that of 17 other host species using data from published studies. Spatial scale explains two thirds of the variance in distance decay rates, and some of the remaining variance is explained by latitude. The rate of decay in parasite community similarity with distance is greater in larger scale studies and further away from the equator. Traits of host species traits such as vagility, body weight and trophic level have little or no effect on distance decay rates.     

Intercolony variation in foraging flight characteristics of black‐headed gulls Chroicocephalus ridibundus during the incubation period

Using GPS loggers, we examined the influence of colony, sex, and bird identity on foraging flight characteristics of black‐headed gulls Chroicocephalus ridibundus during the incubation period. We studied tracks of 36 individuals breeding in one urban and two rural colonies in Poland. Birds from both rural colonies performed the furthest flights (mean max distance 8–12 km, up to 27 km) foraging mainly in agricultural areas. Gulls from the urban colony performed shorter flights (mean 5 km, up to 17 km) visiting mainly urbanized areas and water bodies. We found that females performed longer flights and their flight parameters were less repeatable compared to males. Males from both rural colonies visited water bodies more frequently than females. In all colonies, males (but not females) used habitats unproportionally to their availability in the vicinity. Relatively low interindividual and relatively high intraindividual overlap in home ranges indicated considerable foraging site fidelity. Individuals specialized in the use of a particular type of habitat performed shorter foraging flights compared to individuals using diverse habitats during their foraging flights. Our results indicate diverse foraging strategies of black‐headed gulls, including generalists that explore various habitats and specialists characterized by high foraging site and habitat fidelity.     

Breeding adaptations of Franklin's gull (larus pipixcan) to a marsh habitat

The behaviour and ecology of Franklin's gull were studied at Agassiz National Wildlife Refuge in northwestern Minnesota to determine the adaptations of the species for nesting in marshes. Two factors seemed to be important in colony site selection: cattail dispersion pattern and cattail density. Franklin's gulls prefer to nest in cattail areas closest to open water. The number of nests per unit area decreased as cattail density increased. Nest site selection is dependent on aggression and visibility. Visibility from nest level is the result of cattail placement and height. The distance between nests was directly correlated with visibility. Aggression by gulls on nests was lowered experimentally by decreasing visibility and raised by increasing visibility. Nest platforms were constructed of cattail material, and were attached to cattail stems. Nest material was added to the nests throughout the incubation and brooding period. Material was usually added following nest relief. The egg laying period was from 6 to 28 May. There was more synchrony of egg laying in sub-areas of the colony than in the colony as a whole. Successive eggs in clutches were laid at 24- to 48-hr intervals. The distance between nests decreased during the season as pairs filled in areas that were not defended. Territorial pairs defended an area up to 10 m from their stations prior to egg laying, but defended only the area within 3 m of their nests during incubation. Both members of pairs incubated the eggs and cared for the young. The incubation period was 24 days. The primary predators on adults and young were marsh hawk, great horned owl and mink. Franklin's gulls do not eat eggs or young of gulls. Adults fed on earthworms, insects and grain. Most marked adults fed within 16 km of the colony. Chicks were fed primarily on earthworms. The hatching period was from 30 May to 21 June. Chicks of all ages tested on a visual cliff apparatus were able to perceive the drop. Chicks tested on a 30-degree incline apparatus walked up it when 6 days old and younger, and walked down at 12 days of age and older. Brood mobility was less than in ground nesting species of gulls. In an undisturbed colony the chicks remained on the nest platforms until they were 25 to 30 days old although they were capable of swimming shortly after hatching. Individual recognition between parents and chicks appeared later in this species than in ground-nesting gulls. Adults accepted alien chicks (experimentally exchanged) that were younger than about 14 days old until their own chicks were over that age. Adults accepted larger and older broods than their own, as well as broods of mixed ages. Chicks began to react differently to strange adults at about 16 days of age. The breeding chronology of Franklin's gull is compressed when compared to that of other gulls. Possible selection pressures affecting this synchrony are discussed. The behaviour of the marsh-nesting Franklin's gull is compared with that of typical ground-and cliffnesting gulls; the possibility that the ancestral gull may have been a marsh nester is discussed.     

Corvids congregate to breeding colonies of a burrow‐nesting seabird

Egg predation is a major cause of reproductive failure among birds, and can compromise the viability of affected populations. Some egg predators aggregate near colonially breeding birds to exploit the seasonal increase of prey resources. We investigated spatial and temporal variations in the abundance of an egg predator (little raven Corvus mellori; Corvidae) to identify whether ravens aggregate spatially or temporally to coincide with any of three potential prey species: burrow‐nesting little penguin (Eudyptula minor; Spheniscidae), short‐tailed shearwater (Ardenna tenuirostris; Procellariidae), and surface‐nesting silver gull (Chroicocephalus novaehollandiae; Laridae). We derived spatially explicit density estimates of little ravens using distance sampling along line transects throughout a calendar year, which encompassed little penguin, short‐tailed shearwater and silver gull breeding and non‐breeding seasons. High raven abundance coincided temporally with penguin and gull egg laying periods but not with that of shearwaters. The spatial distribution of raven density corresponded with the little penguin colony but not with shearwater or gull colonies. Thus, the presence of little penguin eggs in burrows correlated strongly with little raven activity, and this implies that little ravens may have learnt to exploit the plentiful subsurface food resource of little penguin eggs. Corvid management may be required to maintain the viability of this socially and economically important penguin colony.     

High connectivity in a long-lived high-Arctic seabird,the ivory gull <Emphasis Type="Italic">Pagophila eburnea</Emphasis>

Species may cope with rapid habitat changes by distribution shifts or adaptation to new conditions. A common feature of these responses is that they depend on how the process of dispersal connects populations, both demographically and genetically. We analyzed the genetic structure of a near-threatened high-Arctic seabird, the ivory gull (Pagophila eburnea) in order to infer the connectivity among gull colonies. We analyzed 343 individuals sampled from 16 localities across the circumpolar breeding range of ivory gulls, from northern Russia to the Canadian Arctic. To explore the roles of natal and breeding dispersal, we developed a population genetic model to relate dispersal behavior to the observed genetic structure of worldwide ivory gull populations. Our key finding is the striking genetic homogeneity of ivory gulls across their entire distribution range. The lack of population genetic structure found among colonies, in tandem with independent evidence of movement among colonies, suggests that ongoing effective dispersal is occurring across the Arctic Region. Our results contradict the dispersal patterns generally observed in seabirds where species movement capabilities are often not indicative of dispersal patterns. Model predictions show how natal and breeding dispersal may combine to shape the genetic homogeneity among ivory gull colonies separated by up to 2800 km. Although field data will be key to determine the role of dispersal for the demography of local colonies and refine the respective impacts of natal versus breeding dispersal, conservation planning needs to consider ivory gulls as a genetically homogeneous, Arctic-wide metapopulation effectively connected through dispersal.     

Collective aggressiveness limits colony persistence in high‐ but not low‐elevation sites at Amazonian social spiders

Identifying the traits that foster group survival in contrasting environments is important for understanding local adaptation in social systems. Here, we evaluate the relationship between the aggressiveness of social spider colonies and their persistence along an elevation gradient using the Amazonian spider, Anelosimus eximius. We found that colonies of A. eximius exhibit repeatable differences in their collective aggressiveness (latency to attack prey stimuli) and that colony aggressiveness is linked with persistence in a site‐specific manner. Less aggressive colonies are better able to persist at high‐elevation sites, which lack colony‐sustaining large‐bodied prey, whereas colony aggression was not related to chance of persistence at low‐elevation sites. This suggests that low aggressiveness promotes colony survival in high‐elevation, prey‐poor habitats, perhaps via increased tolerance to resource limitation. These data reveal that the collective phenotypes that relate to colony persistence vary by site, and thus, the path of social evolution in these environments is likely to be affected.     

The biological function of gulls' attraction towards predators

Many species of birds and mammals are attracted towards some of their natural predators, often without overt aggression. The biological function of this predator attraction was studied in a colony of herring gulls and lesser black-backed gulls, with the aid of predator models. More birds flocked above the predator model when it was presented together with a dead gull; also the birds did not land as close to a predator with a dead gull as they did to a predator alone. Having seen a predator with a dead gull had a clear effect on the distance at which birds later avoided that particular predator on the ground when it was presented to them alone. It is suggested that predator-attraction enables animals to collect information about a potential enemy; in this information the experience of conspecifics with the predator is taken into account; subsequent behaviour of the animals depends partly on this information. The increase in the avoidance distance with respect to a predator with a dead bird may be an adaptation to carnivores' habit of surplus killing.     

The effects of heterospecifics and climatic conditions on incubation behavior within a mixed‐species colony

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.     

Fine‐scale genetic structure reflects sex‐specific dispersal strategies in a population of sociable weavers (Philetairus socius)

Dispersal is a critical driver of gene flow, with important consequences for population genetic structure, social interactions and other biological processes. Limited dispersal may result in kin‐structured populations in which kin selection may operate, but it may also increase the risk of kin competition and inbreeding. Here, we use a combination of long‐term field data and molecular genetics to examine dispersal patterns and their consequences for the population genetics of a highly social bird, the sociable weaver (Philetairus socius), which exhibits cooperation at various levels of sociality from nuclear family groups to its unique communal nests. Using 20 years of data, involving capture of 6508 birds and 3151 recaptures at 48 colonies, we found that both sexes exhibit philopatry and that any dispersal occurs over relatively short distances. Dispersal is female‐biased, with females dispersing earlier, further, and to less closely related destination colonies than males. Genotyping data from 30 colonies showed that this pattern of dispersal is reflected by fine‐scale genetic structure for both sexes, revealed by isolation by distance in terms of genetic relatedness and significant genetic variance among colonies. Both relationships were stronger among males than females. Crucially, significant relatedness extended beyond the level of the colony for both sexes. Such fine‐scale population genetic structure may have played an important role in the evolution of cooperative behaviour in this species, but it may also result in a significant inbreeding risk, against which female‐biased dispersal alone is unlikely to be an effective strategy.     

Foraging distances of a resident yellow-legged gull (Larus michahellis) population in relation to refuse management on a local scale

Seasonal fluctuations in marine prey availability around breeding colonies are one of the major factors affecting resident behaviour in seabirds. This is particularly applicable to large gulls (Larus spp.). The effect of refuse management on large gulls has been studied chiefly in relation to breeding dynamics, but it is less understood with regard to movement patterns. Our aim was to test whether the closure of one large dump and the use of falconry to deter gull access to two others, within the southeastern Bay of Biscay area, affected the foraging distance of local yellow-legged gulls (Larus michahellis). During a period of seven consecutive winters between 2005 and 2011, the proportion of gulls that moved less than 50 km from their natal site was 70 %. However, during the winter of 2010, when they were deterred from accessing refuse tips within the region, gulls were found to travel longer distances. This result was explained neither by a decreasing survey effort near colonies nor by a decrease in apparent availability of marine prey, thus supporting the hypothesis that refuse management within the region influenced the movement patterns of local gulls.     

Equal reproductive success of phenotypes in the Larus glaucescens–occidentalis complex

Glaucous‐winged gulls Larus glaucescens and western gulls L. occidentalis hybridize extensively where their ranges overlap along the coasts of Washington and Oregon, producing a continuum of phenotypic intergrades between the two parental species. This zone often is considered an example of geographically bounded hybrid superiority, but studies of relative success among parental types and hybrids have not provided consistent support for this model. We tested the predictions of the dynamic‐equilibrium and geographically bounded hybrid superiority hypotheses by studying mate choice and reproductive success among gulls on Protection Island, Washington, the largest breeding colony of glaucous‐winged/western gulls within the hybrid zone. The dynamic‐equilibrium hypothesis posits that hybridization due to dispersal balances selection against less fit hybrids and assortative mating is adaptive. Geographically bounded hybrid superiority posits that hybrids are better fit than parental types within an ecotone between the environments to which the parental species are adapted, and a preference for hybrid mates is adaptive. Additionally, we investigated whether hatching success and nest site choice are correlated for Protection Island gulls. We assigned a hybrid index to each sample bird by examining plumage melanism and bare part coloration in the field. Sheltered nests contained larger clutches and exhibited increased hatching success, but choice of nest habitat was not associated with hybrid index. Western gull‐like pairs produced smaller third eggs; however, hybrid index was not correlated with clutch size or hatching success. Protection Island gulls did exhibit assortative mating. In short, we did not find strong support for either geographically bounded hybrid superiority or the dynamic‐equilibrium hypothesis.     

A gravel-covered iceberg provides an offshore breeding site for ivory gulls <Emphasis Type="Italic">Pagophila eburnea</Emphasis> off Northeast Greenland

The ivory gull Pagophila eburnea is an Arctic seabird species whose distribution is tightly coupled to the availability of sea ice. During the last decades, strong declines have been reported for breeding colonies in Canada and Greenland, which are usually located on nunataks or remote coastal islands. Here, we report the observation of a colony of ivory gulls breeding on a gravel-covered iceberg 70 km off Northeast Greenland in August 2014. It concerned approximately 60 adults, including two ringed individuals, and many chicks. This represents an unusual breeding site for the species, to be compared with a few cases of colonies on gravel-covered sea ice. Breeding on an offshore iceberg may be advantageous since it provides ultimate protection from predators. Furthermore, the proximity to the productive North East Water polynya may have been attractive to these gulls. As a consequence of this and previous observations, colony surveys should not solely focus on inland and coastal breeding habitats, but should be extended towards the ocean.