Gull Colonies Research Articles

Colonization of lichens on Surtsey 1970–2006

A list of lichen species from the volcanic island Surtsey is presented. A total of 87 species have been recorded since the first three species appeared in 1970. Notes on distribution and short description of the main lichen communities are given. Possible colonization routes to the island are discussed. Four of the species treated are new to iceland, Gyalidea fritzei and Psilolechia clavulifera and two species, one Lecanora and one Stereocaulon which probably are new to science. Two further species belonging to Lecanora, provisionally determined as L. albescens and L. semipallida, are probably new to iceland. The primary colonization resembles what has been recorded on other lava fields in iceland. Lichen species established very slowly on Surtsey with relatively few species found during the first two decades, in 1984 only 17 species had been recorded. That number almost doubled during the next six years, 31 species had been recorded on the island by 1990 and there has been a constant accumulation of species since then. The lichen colonization benefitted from the activity of gulls. Many species were probably dispersed by the trampling birds and colonized the naked lava rock around the breeding area. Later soil formation started in connection with the gull colony and the first colonizers were replaced by other species. The palagonite tuff has only recently been colonized by lichens and on the coastal rocks of the island only one lichenized species has been found so far.

The land-invertebrate fauna on Surtsey during 2002–2006

Formal studies on invertebrate colonizers and establishments on Surtsey started in 1965 and the island was visited regularly for longer and shorter periods till 1984. After a period of sporadic invertebrate studies, yearly visits to Surtsey started again in 2002. Here are presented the results from a five year study period, 2002–2006. Surtsey is characterized by three kinds of substrates, viz. lava, sand and palagonite rock. The invertebrate collecting is mainly based on pitfall trapping in permanent plots on sand and lava substrates, also informing on the impact of a gull breeding colony that started in the lava field in 1985. Netting and direct picking takes place on all three kinds of substrates of the island. Also, three traps were set up close to the hut and helicopter platform to test for signs of human impact. Hitherto, 354 species or taxa ranked as species have been found on Surtsey. Thereof 144 are regarded permanent settlers. in 2005 an invasion of flying insects by air mass was witnessed. Transport of invertebrates by birds was probably underestimated in the beginning, but the existence of a number of permanently settled species can hardly be explained differently. The gull breeding colony was an advantage to the invertebrate diversity on Surtsey. Higher species diversity is found within the colony than outside it and a clear distinction in species composition between plots outside and within the gull colony. Also, a great faunal diversity is within the colony while the fauna is rather homogenous on the sand substrate. Land-invertebrates have proved to play a very important role in the developing ecosystem on the island, also forming the basis for colonization of invertebrate feeding birds.

Formation of a bird community on a new island, Surtsey, Iceland

The present paper summarizes bird observations from Surtsey, iceland since the formation of the island in 1963 until 2008. Continuous observations were maintained in the early years of the island; in spring and autumn 1967–1971 and summers 1970–1973. Since then much of the bird observations are incidental by various scientists and bird watchers visiting the island for a limited period. Different aspects of the bird fauna are examined, the at-sea bird community, vagrants, migrant species, and winter birds, while emphasis is placed on the formation of the breeding bird community. With increasing numbers of breeding species and size of breeding populations as the years passed more structured census of the breeders was needed. Hence whole island censuses were organized in 1990 and 2003. Ringing has been carried out on five occasions. in total 91 bird species have been recorded on or offshore from the island. The first birds started breeding in 1970, Black Guillemot Cepphus grylle and Fulmar Fulmarus glacialis. A total of fourteen species have since bred on the island. Four species of large gulls breed (mostly in one colony); Great Black-backed Gull Larus marinus (bred first in 1974), Herring Gull Larus argentatus (1981), Lesser Black-backed Gull Larus fuscus (~1985), and Glaucous Gull Larus hyperboreus (1993). The colony, starting to form in 1984, has been particularly important for furthering the development of plant and invertebrate communities. Through the fertilizing agency complete vegetation cover is now found in the oldest part of the gull colony. This development has paved the way for terrestrial birds to start breeding; Snow Bunting Plectrophenax nivalis (1996), Greylag Goose Anser anser (~2001) and Meadow Pipit Anthus pratensis (~2003). other breeding species are kittiwake Rissa tridactyla (1975) and White Wagtail Motacilla alba (~2003), but Arctic Tern Sterna paradisaea (1975) has not bred since 1978. in 1990 the island had 316 breeding pairs of six species. in 2003 eleven species bred on the island with a total of about 850 breeding pairs. After 2003 two more species have started breeding, Common Puffin Fratercula arctica (2004) and Raven Corvus corax (2008). Surtsey island was entered on the UNESCo World Heritage list in 2008, not the least for the long history of research and monitoring of various aspects of the island’s natural history. As the breeding bird fauna develops a structured bird monitoring program becomes the more important. Recommendations on how this should be carried out are presented in the paper.

Investigation of the funga of Surtsey 2008

In August 2008 eighteen specimens of at least ten species of agarics (mushrooms) were collected on Surtsey. Entoloma sericeum was well established in grassland in the oldest part of the gull colony and at least seven ectomycorrhizal species, Hebeloma collariatum, H. marginatulum, H. mesophaeum, H. vaccinum var. vaccinum, Inocybe lacera var. lacera, Laccaria laccata and an unidentified Cortinarius species, were collected near their Salix hosts. one Psilocybe species, P. inquilinus, and one unidentified Entoloma species grew in Leymus dunes. Three collections identified to the genus Entoloma and three to the genus Hebeloma could represent two additional species. The findings in 2008 increase the total number of agarics from two to nine and of species of fungi on Surtsey from 26 to 33, counting only those which have been identified to species.

Temporal variations in the concentration and isotopic signature of ammonium- and nitrate–nitrogen in soils under a breeding colony of Black-tailed Gulls (Larus crassirostris) on Kabushima Island, northeastern Japan

Abstract Temporal variations in the concentration and N isotopic ratios of inorganic N (NH4– and NO3–N) as affected by the soil temperature regime together with the input of bird excreta were analyzed in a sedentary soil under a dense colony (1.6 nests/m2) of breeding Black-tailed Gulls (Larus crassirostris: a ground-nesting seabird). Surface soil samples were taken monthly from mid-March to late July 2005 from Kabushima Island, Hachinohe, northeastern Japan. The spatial concentration of inorganic N in the soils varied considerably on all sampling dates. There may be a statistically significant trend, showing increased NH4–N content from settlement up to early June when the input of fecal N attains its maximum, and then decreases towards the end of breeding activity (early August). Abundant NO3–N was observed in all soils, particularly in the later stage of breeding (up to 3800 mg-N/kg dry soil), refuting earlier claims that nitrification is unimportant in the soils. δ15N values of NH4 in the soils showed unusually high values up to +51‰, reflecting N isotope fractionation due to volatilization of NH3 during the mineralization. Mean δ15N values of the monthly collected totals of NH4 and NO3 were not significantly different at the 5% level based on ANOVA and significant differences were observed only among the three means of NO3–N collected in mid-March (settlement of colony: δ15N = −0.2 ± 3.5‰) and late July (later stages of breeding: δ15N = +22.1 ± 7.0‰, +23.3 ± 7.8‰) at the 1% and 5% levels by t-test, respectively. Such an observation of significantly increased δ15N values for NO3–N in soils from the fledgling stage indicates the integration of denitrification coupled with nitrification under a limited supply of fecal N.

Impact of egg harvesting on breeding success of black-headed gulls, Larus ridibundus

Gull colonies world-wide have been harvested for their eggs for centuries with minimal knowledge of the impacts on breeding. Although most Laridae can replace lost eggs, they have comparatively high energetic demands for egg production. In this paper we assess the impacts of a licensed egg harvest on the breeding success of black-headed gulls Larus ridibundus, which nest colonially in an EU Special Protection Area in Hampshire, southern England. We compared egg volume, hatching and chick survival from harvested and un-harvested nests in central and fringe positions within colonies of various sizes, including colonies with no harvesting activity. Eggs from various laying stages were collected from harvested and un-harvested colonies of similar pre-harvest intrinsic quality, for comparison of their volumes, yolk-to-albumen ratios and eggshell thickness. Egg volume and the yolk-to-albumen ratio depended on laying time and location, with the largest eggs laid during the peak period by birds breeding in central positions on large colonies. Eggs produced by these peak layers also had the largest yolk-to-albumen ratios. Harvested sites were characterised by reductions in egg volume, yolk-to-albumen ratio and eggshell thickness, which translated to poorer hatching success and chick survival. Harvested sites also had a higher proportion of abnormal eggs, particularly taking the forms of small yolkless eggs and unpigmented eggs. The reduced breeding success on harvested colonies is likely to be linked to depletion of the female's endogenous reserves which can also reduce future survival and breeding propensity.

Gull Predation and Breeding Success of Common Eiders on Stratton Island, Maine

Common Eider (Somateria mollissima dresseri) breeding success and gull-eider interactions were studied at Stratton Island, Maine in 2004 and 2005. Eiders suffered little nest predation, and most egg losses to gulls were either facilitated by researcher intrusions or confined to newly initiated, unattended nests. Despite high nest success (>80%) in both study years, predation watches indicated that few, if any, ducklings survived to fledging as a result of extreme harassment and predation by Great Black-backed Gulls (Larus marinus). Gull attacks were opportunistic, involved one to 36 gulls, and often resulted in complete crèche destruction. Herring Gulls (L. argentatus) also took occasional young and eggs. Although Stratton Island is managed as a tern restoration site, and gull control measures to enhance tern productivity include nest destruction and shooting of tern predators, gulls continued to congregate around crèching areas and to prey on ducklings. We suggest that additional gull control measures, particularly at a nearby gull colony, may enhance duckling survival. We also recommend monitoring of other eider colonies in the region to better assess duckling survival and recruitment rates.

Compromise between seabird enjoyment and disturbance: the role of observed and observers

SUMMARYNatural areas are increasingly visited by people, and urban human visitors expect to watch wildlife as close as possible, but this may have associated disturbance costs. Here, effects of number of visitors and bird density on flight initiation distance (FID) as a proxy of disturbance vulnerability were evaluated in the large ground-nesting yellow-legged gull,Larus michahellis. Mean FID decreased with increasing number of visitors and with increasing gull densities, suggesting that (1) ground-nesting gulls habituate to massive human presence, while retaining their antipredatory mechanisms, and (2) dense groups of gulls were more reluctant to fly away. This density effect may be due to the increased risk of clutch predation by conspecifics at high densities and, if so, FID is a reliable metric of disturbance vulnerability in ground-nesting gulls. In conclusion, set-back distances are specific to local populations and it is unnecessary to ban or restrict human visits to ground-nesting gull colonies; redistributing visits, taking into account both the number of visitors and gull density, is preferable.

ORIGINAL ARTICLE: Turnover of plants on small islets of the eastern Aegean Sea within two decades

AbstractAim To estimate species turnover of plants on 32 small islands within a 20‐year period and to assess possible changes in community composition and properties, such as species richness and factors affecting it, nestedness, species co‐occurrence and overall community similarity. Additionally, to assess the possible effects of grazing, gull colonies and fire on turnover values.Location Thirty‐two islets in the eastern Aegean Sea (Greece).Methods Complete sampling of plants was performed in 1974 and in 1990–94 (mostly in 1994, which was used as the reference year). Species turnover rates were estimated using both per island and per species approaches. Multiple regression was used to evaluate factors affecting species richness. Chi‐square tests were applied to compare community composition among sampling periods. The effects of various factors on turnover rates and species richness were examined using one‐way anova and ancova. Mann–Whitney tests were applied in order to check for differences between frequencies of occurrence of extinct, immigrant and persisting species. Community nestedness was calculated using bitmatnest and the C‐score index for co‐occurrence was estimated using EcoSim7. Species similarities among islands in each of the 1974 and 1994 data sets were assessed using Jaccard’s index and the two similarity matrices were compared using a Mantel test.Results Of 391 species recorded on the islets, 334 were present in 1974, 301 in 1994 and 244 were common to both these periods. Species richness in the 1974 and 1994 data sets was significantly correlated with elevation and area, but not with distance from the nearest large island. Richness was positively affected by grazing, but not by fire or gull colonies. The slopes of species–area and species–elevation regressions were almost identical in 1974 and 1994. Mean relative turnover was 2.06 (species per islet) and 3.26 (islets per species). Turnover was not correlated with area, elevation or distance from the nearest large island. Nestedness and co‐occurrence levels were very similar. Tables of islet by islet floral similarity (Jaccard’s index) did not differ between the 1974 and 1994 data sets.Main conclusions The turnover rates found are among the highest recorded for plants; at the same time the islet communities exhibit notable stability in overall properties. Our results provide evidence for rapid shifts in species number that may nonetheless be considered as equilibrial dynamics, as these islets are able to respond rapidly to environmental change and disturbance. Human activities, notably the application of grazing, have a significant complicating effect on community dynamics, enhancing observed turnover rates.

First survey of Audouin’s Gull, Larus audouinii (Payraudeau, 1826), colonies at Kleidhes Islands, Cyprus

Breeding numbers of Audouin's Gulls were assessed during spring 2007 at Kasteletta and Zinaritou Islands, Kleidhes Islands, Cyprus. The colony on Kasteletta was small, holding six nests, and was abandoned early most probably because of the presence of a much larger Yellow-legged Gull colony on the same island. The colony on Zinaritou had 43 nests and a high breeding success, with nearly one fledgling per pair and 37% of chicks surviving (as a percentage of eggs laid). Low levels of interspecific competition with Yellow-legged Gulls, habitat suitability, protection from human disturbance and nearby trawling fishing activity probably contributed to the success of this colony.

Distribution of breeding sites and food constrains size and density of yellow-legged gull colonies

In this study, we aimed to identify the factors determining the size and density of yellow-legged gull colonies (Larus michahellis) on rocky islands. We considered both island geography and topography, as well as food resources availability, as potential constraining factors. Our censuses conducted on 43 islands and islets along 80 km of the French Mediterranean coastline contained the largest French yellow-legged gull populations (20 914 breeding pairs). Multiple linear regression models determined that colonization history and island area primarily determine colony size population density was also associated to colonization history, island characteristics, anthropogenic food resource availability, and human activities (R 2 = 63.7%). We conclude that breeding site selection by yellow-legged gulls seems to fulfill the known topographic requirements for the breeding sites of this species while minimizing the distance to its known foraging habitat in the area (landfills).

Microbiological survey for selected bacterial pathogens in European storm petrel (Hydrobates pelagicus, Linnaeus 1758) from Grosa Island (Murcia, Southeastern Spain)

The current work shows the first step in the knowledge on the health status of European storm petrel (Hydrobates pelagicus) colony inhabiting Grosa Island (Murcia, SE Spain). We performed a screening about the bacterial pathogens carried by them (among the infectious agents checked, bacteria of the orders Mollicutes and Chlamydiales, and the genera Salmonella are of main interest) and compare these results with similar works performed in Larus species because most of the breeding colonies of storm petrel share habitats with gull colonies, and these could become pathogen reservoirs to petrels. Our results show the European storm petrels sampled have absence of pathogens of main interest and low levels of opportunistic pathogens. No Mycoplasma species were isolated, and no Chlamydophila psittaci were demonstrated by lipopolysaccharide antigen immunodetection. The commensal bacteria were isolated in higher frequencies than the previous [Staphylococcus epidermidis (5/15), Staphylococcus hominis (2/15) and Staphylococcus aureus (1/15)]. The rate of isolation of Gram-negative was lower than in the previous Gram-positive bacteria [Pasteurella sp. (1/15) and Pseudomonas aeruginosa (1/15)], and no Enterobacteriaceae were isolated. The absence of pathogen carriers on European storm petrel is the main conclusion of this survey; it is an evidence that the bacterial infectious pathogens described in gulls may not be an important selective force on their survival.

Impact of Raccoons on Breeding Success in Large Colonies of Great Black-backed Gulls and Herring Gulls

For most ground-nesting seabirds, offshore islands usually serve as refuges from mammalian predators, however, introduced predators pose a substantial threat to many species. In New England, thousands of Herring Gulls (Larus argentatus) and Great Black-backed Gulls (L. marinus) breed on hundreds of coastal islands. The Isles of Shoals (New Hampshire/Maine) archipelago has some of the largest colonies of both gull species in New England. In 2004, we noted unusually large numbers of failed nests on Appledore Island, Maine and hypothesized that Raccoons (Procyon lotor) were the cause. Therefore, we quantified egg and chick mortality and documented the presence of Raccoons. We trapped Raccoons on Appledore and Smuttynose islands and conducted nest surveys on these and two other islands in the Isles of Shoals. Surveys of marked nests on Appledore Island revealed high levels of egg and chick mortality in early June 2004; by late June 58% of nests were empty. We also found that on Appledore and Smuttynose, where Raccoons were observed, the odds that a nest would be empty were 17 times greater than on Lunging or Duck Islands where no Raccoons were observed. During 2004, eleven Raccoons were trapped off of Appledore and Smuttynose Islands. A survey of nests in 2005 showed that gull breeding success increased significantly on Appledore and Smuttynose islands, whereas there was no significant change in the relatively high ratio of chicks to nests from 2004 to 2005 on Lunging Island where Raccoons were not observed. Thus, we concluded that the presence of a few Raccoons on Appledore and Smuttynose islands was sufficient to cause substantial breeding failure in large colonies of larids.

Diet variability of Mediterranean insular populations of Rattus rattus studied by stable isotope analysis

The black rat Rattus rattus is a successful colonizer that threatens native species on numerous islands. Stable isotopes of carbon and nitrogen were used to quantify the rat diet on islands off the southern French coast. Samples of rat hair and faeces and their potential food were collected on each island. The nitrogen isotopic values of invertebrates and vegetation on Riou (near Marseille) differed from the other two islands (Hyères archipelago). This was attributed to a large colony of gulls on Riou, of which rats take great advantage. A part of the observed variability was due to methodological skews: two kinds of hair gave different results and there was an effect of the season and year of sampling but inter-island differences were noticeable. In certain cases, the food source value from plants and invertebrates could supply the total food needs of rats as there was no evidence of consumption of eggs, chicks or birds.

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

AbstractYellow‐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.

Expansion of the Mediterranean Gull Larus melanocephalus in Poland

Since 1981, when the first breeding pair of Mediterranean Gull Larus melanocephalus was recorded in Poland, the population of this gull has increased considerably. Its population size was stable until 1997, not exceeding ten pairs annually; thereafter, an increasing number of sightings were made, and during the last 5 years between 26 and 39 breeding pairs have been recorded in Poland. To date, breeding sites have been established in a total of 45 sites (maximum of 19 sites in a given year), with 27% of these (43% of all broods) found on islands located in the middle course of the Vistula River. Breeding sites have also included artificial reservoirs, such as dam reservoirs (20% of sites, 19% of broods), gravel pits (9% of sites, 13% of broods) and fishponds (24% of places, 8% of broods). Mediterranean Gulls were found to nest only within the colonies of other Laridae. Single pairs were recorded at 40% of the breeding sites, whereas a maximum of two to five pairs were recorded at 47% of the other sites. The great majority of breeding attempts were recorded in Black-headed Gull L. ridibundus colonies. In two cases, Mediterranean Gulls bred within mono-specific colonies of Common Gulls L. canus consisting of 60–150 pairs. The biggest concentrations of breeding sites were along the middle course of the Vistula river and in the southern part of Poland.

Modeling territory attendance and preening behavior in a seabird colony as functions of environmental conditions

In previous studies we developed a general compartmental methodology for modeling animal behavior and applied the methodology to marine birds and mammals. In this study we used the methodology to construct a system of two differential equations to model the dynamics of territory attendance and preening in a gull colony on Protection Island, Strait of Juan de Fuca, Washington. We found that colony occupancy was driven primarily by abiotic environmental conditions, including tide height, time of day, solar elevation, and wind speed over open water. For birds in the colony, preening behavior was driven to some extent by abiotic environmental conditions (including time of day, solar elevation, humidity, and wind speed on the colony), but apparently was driven primarily by local and/or biotic effects not included in the model. In terms of R 2 values, the model explained 65% and 37% of the variability in colony occupancy and preening data, respectively, as a function of these six abiotic environmental factors.

Seasonal Timing of Bald Eagle Attendance and Influence on Activity Budgets of Glaucous-winged Gulls in Barkley Sound, British Columbia

Abstract As raptor populations recover following the banning of organochlorine pesticide use, there may be consequences for prey populations. While Bald Eagles (Haliaeetus leucocephalus) actively prey on Glaucous-winged Gulls and their offspring (Larus glaucescens), their presence at colonies and roost sites may also influence reproductive success of gulls by impacting activity budgets. Here we investigate changes in Bald Eagle abundance in relation to gull breeding phenology over 6 years at Seabird Rocks (Vancouver Island, Canada) and compare activity budgets of gulls in relation to Bald Eagle abundance. Bald Eagle abundance varied seasonally, peaking during late incubation and hatching of gull eggs. As Bald Eagle presence increased, gulls showed a strong increase in time allocated to vigilance (54%) and frequency of flushing (up to 6 times/hr). These results indicate that Bald Eagle attendance patterns at gull colonies coincide with hatching of gull chicks and can influence time-activity budgets of gull...

Impact of wind turbines on birds in Zeebrugge (Belgium)

We studied the impact of a wind farm (line of 25 small to medium sized turbines) on birds at the eastern port breakwater in Zeebrugge, Belgium, with special attention to the nearby breeding colony of Common Tern Sterna hirundo, Sandwich Tern Sterna sandvicensis and Little Tern Sterna albifrons. With the data of found collision fatalities under the wind turbines, and the correction factors for available search area, search efficiency and scavenging, we calculated that during the breeding seasons in 2004 and 2005, about 168 resp. 161 terns collided with the wind turbines located on the eastern port breakwater close to the breeding colony, mainly Common Terns and Sandwich Terns. The mean number of terns killed in 2004 and 2005 was 6.7 per turbine per year for the whole wind farm, and 11.2 resp. 10.8 per turbine per year for the line of 14 turbines on the sea-directed breakwater close to the breeding colony. The mean number of collision fatalities when including other species (mainly gulls) in 2004 and 2005 was 20.9 resp. 19.1 per turbine per year for the whole wind farm and 34.3 resp. 27.6 per turbine per year for 14 turbines on the sea-directed breakwater. The collision probability for Common Terns crossing the line of wind turbines amounted 0.110–0.118% for flights at rotor height and 0.007–0.030% for all flights. For Sandwich Tern this probability was 0.046–0.088% for flights at rotor height and 0.005–0.006% for all flights. The breeding terns were almost not disturbed by the wind turbines, but the relative large number of tern fatalities was determined as a significant negative impact on the breeding colony at the eastern port breakwater (additional mortality of 3.0–4.4% for Common Tern, 1.8–6.7% for Little Tern and 0.6–0.7% for Sandwich Tern). We recommend that there should be precautionary avoidance of constructing wind turbines close to any important breeding colony of terns or gulls, nor should artificial breeding sites be constructed near wind turbines, especially not within the frequent foraging flight paths.

Nutrient transfer from sea to land: the case of gulls and cormorants in the Gulf of Maine

1. The structure of communities is influenced by the transport of resources across ecosystem boundaries. Seabirds are capable of introducing large amounts of marine-derived nutrients to land, thereby modifying resource availability to terrestrial species. 2. In this study we investigated the hypothesis that variation in nesting densities of great black-backed gulls Larus marinus and double-crested cormorants Phalacrocorax auritus would modify the effect of these species on soil nutrients and plant species composition on offshore islands in the Gulf of Maine, USA. 3. Our results showed a significant positive correlation between nest density and concentrations of ammonia and nitrate in soils, but no significant relationship between nest density and phosphate. Ammonia and phosphate concentrations were good predictors of plant species composition; there were more annual forbs than perennial grasses in the abandoned cormorant colony compared with the gull colonies. Extremely high concentrations of ammonia in the highest density colony (active cormorant) may have been the main factor inhibiting plant germination at this site. All of the plant species in gull and cormorant colonies showed enriched delta(15)N signatures, indicating substantial input of marine-derived nitrogen from seabirds. 4. Our study demonstrated that gulls and cormorants are effective vectors for the transport of marine nutrients to terrestrial ecosystems. However, transported nutrients occurred in particularly high concentrations in areas with nesting cormorants. Nesting densities and species-specific variation in resource transport should be considered when predicting the effects of seabirds and other biogenic vectors of allochthonous resources.