Black-tailed Gull Larus Crassirostris Research Articles

Comparing spatial differences in behavioral pattern transition of Black-tailed gull during post breeding season in the Korean peninsula

Parents adjust their foraging effort according to the chick and their own body condition and dual foraging strategy is one of the foraging tactics parents replenish their own reserves while feeding their chicks. During the post-breeding season, seabirds disperse to recover their own body condition and prepare for the next breeding season. Recently, we discovered Black-tailed gulls (Larus crassirostris) breeding around the Korean Peninsula occasionally foraging long trips during the late fledging, however, our understanding of the behavioral patterns of Black-tailed gulls during the late fledging and post-breeding, as well as its inter-colonial differences, remains considerably limited. Here, we employed 92 GPS trackers to adult Black-tailed gulls (Larus crassirostris) from six breeding colonies around the Korean peninsula (Yellow Sea—three colonies, South Sea—one colony, and East Sea—two colonies). To determine the foraging investment during the fledging, we suggested the flight efficiency in each trip as the ratio of maximum foraging distance (i.e., straight line distance) to total foraging distance (i.e., sum of all consecutive distance for each trip). Overall, the mean flight efficiency of the long foraging trips were lower than 57% (40.76 ± 13.07%) whereas that of the short foraging trips were over 74% (80.87 ± 4.03%). This may suggest that Black-tailed gulls may visited more than one foraging site during the long foraging trip while they flew directly between the foraging site and breeding colony during the short foraging trip to invest more in their juvenile. Moreover, longer maximum foraging distance with higher flight efficiency observed in the East Sea may indicate a balance between the costs (such as energy expended during foraging or food competition near breeding sites) and the benefits (quantity and quality of food obtained). Our findings revealed the flight behavior of Black-tailed gulls during the late fledging and post breeding, across six breeding colonies, which have different competition pressures and proximity to foraging site.

Mercury monitoring in the coastal areas of the Republic of Korea using the black-tailed gull egg as an indicator

In the southeast and east coasts of the Republic of Korea, it is essential to monitor mercury accumulation in coastal organisms in view of the higher mercury distribution in sediments and human samples. However, mercury pollution monitoring in organisms, especially higher trophic-level organisms that can exhibit high mercury accumulation, is limited. Here, we examined the applicability of the eggs of the black-tailed gull (Larus crassirostris), which belongs to a high trophic level, for mercury monitoring in coastal areas. Breeding sites were selected in West, Southeast, and East Seas with different mercury concentrations in other matrices (sediment and biological samples of residents). The 5-year mean total mercury concentration in eggs collected during the breeding seasons from 2016 to 2020 was lower in Baengnyeongdo (705 ± 81 ng/g dry weight (dry), West Sea) than in Hongdo (1,207 ± 214 ng/g dry, Southeast Sea) and Ulleungdo (1,095 ± 95 ng/g dry, East Sea). The different patterns of mercury concentration in gull eggs among the breeding sites was consistent with those in the other matrices among the coastal areas. These results support the applicability of the black-tailed gull egg as an indicator for establishing a monitoring framework in the coastal areas of the Republic of Korea.

Status of Marine Debris Damage to Adult and Young Black-Tailed Gulls (Larus crassirostris) in Their Breeding Colonies in South Korea

Marine debris from fishing-related paraphernalia poses a threat to the survival of marine organisms, especially seabirds. Although the detrimental effects of marine debris on seabirds have been documented, studies on the extent of damage inflicted by marine debris on the seabird breeding population are scarce. Here, marine debris ingestion and entanglement damage to black-tailed gulls (Larus crassirostris) residing in South Korea were quantified. The five breeding colonies of black-tailed gulls were visited, and the frequency of ingestion and entanglement damage in adults and young were recorded. A total of 25 cases of marine debris damage were confirmed. As a result, damage by marine debris to gulls varied depending on breeding colonies. More adults suffered from entanglement damage than the young, and their most damaged parts were usually their legs. Fishing lines and hooks caused the most damage. We suggest that marine debris damage acquired in breeding colonies could affect breeding success.

Changes in Flight Altitude of Black-Tailed Gulls According to Temporal and Environmental Differences.

In this study, GPS trackers were attached to black-tailed gulls (Larus crassirostris) breeding on five islands in Republic of Korea during April and May 2021, and their flight frequency, behavioral range, and flight altitude were compared during and after the breeding season. During the breeding season, the flight frequency was lowest on Dongman Island (28.7%), where mudflats were distributed nearby, and the range of activity was narrow. In contrast, it tended to be high on Gungsi Island (52%), where the breeding colony was far from land, resulting in a wider range of activity. Although the flight frequency on Dongman Island increased post-breeding season (42.7%), it decreased on other islands. The mean flight altitude during the breeding season was lowest on Dongman Island and highest on Napdaegi Island. In most breeding areas, the mean flight altitude during the post-breeding season was higher than that during the breeding season. However, the lead flight altitude was lower during the non-breeding season compared to that in the breeding season. The home range expanded after the breeding season, with no significant difference in lead time between the breeding and non-breeding seasons. Our findings reveal that black-tailed gulls exhibit varying home ranges and flight altitudes depending on season and geographical location. As generalists, gulls display flexible responses to environmental changes, indicating that flight behavior adapts to the evolving environment over time and across regions.

Integrated approach for the isotope trophic position of black-tailed gull (Larus crassirostris) eggs over a decade: Combining stable isotopes of amino acids and fatty acids composition

Recently, compound-specific isotope analysis (CSIA) using the amino acid nitrogen stable isotope ratio (δ15NAAs) has been widely used for accurate estimation of trophic position (TP). In addition, a quantitative fatty acid signature analysis (QFASA) offers insights into diet sources. In this study, we used these techniques to estimate the TP for seabirds that rely on diverse food sources across multiple ecosystems. This allows for the proper combination of factors used in TP calculation which are different for each ecosystem. The approach involved the application of a multi-mixing trophic discrimination factor (TDF) and mixing β which is a Δδ15N between trophic and source amino acid of primary producer. Since the black-tailed gulls (BTGs) are income-breeding seabirds, which rely on energy sources obtained around their breeding sites, they and their eggs could be useful bioindicators for environmental monitoring. However, the ecological properties of BTGs such as habitats, diets, and TP are not well known due to their large migration range for wintering or breeding and their feeding habits on both aquatic and terrestrial prey. In this study, the eggs were used for estimating TP and for predicting TP of mother birds to overcome difficulties such as capturing birds and collecting non-invasive tissue samples. Eggs, sampled over a decade from three Korean islands, showed spatial differences in diet origin. Considering both the food chain and physiology of BTG, the TP of eggs was estimated to be 3.3–4.0. Notably, the TP was significantly higher at site H (3.8 ± 0.1) than at site B (3.5 ± 0.2), which indicated a higher contribution of marine diet as confirmed by QFASA. Using a reproductive shift of δ15NAAs, the TP of the mother birds was predicted to be 3.6–4.3, positioning them as the top predator in the food web. The advanced integration of multiple approaches provides valuable insights into bird ecology.

Occurrence, dietary influence and risks of selected trace metals in different coastal predatory species

The global issue of ongoing trace metal emissions and legacy accumulation from diverse sources is posing threats to coastal wildlife. This study characterized the distribution of five metals in relation to dietary ecology (carbon and nitrogen stable isotopes: δ15N and δ13C) in representative predatory species (starfish, fish, and seabird) collected from the coast of Qingdao, northeastern China. Zinc (Zn) was the most abundant metal across species, followed by copper (Cu), chromium (Cr), cadmium (Cd), total and methylated mercury (THg and MeHg). Among the studied species, black-tailed gulls (Larus crassirostris) occupied the highest trophic position, followed by three predatory fish species, whereas the northern Pacific seastar (Asterias amurensis) had the lowest trophic position. The starfish exhibited high capacity to accumulate Cd, Cr and Cu. Conversely, black-tailed gulls exhibited high levels of Zn, while Hg was highest in predatory fishes. Across species, Cr, MeHg, THg and MeHg:THg showed significant positive correlations with δ13C, suggesting the influence of inshore food sources on their accumulation. Both MeHg and THg were significantly and positively correlated with δ15N, with MeHg demonstrating a greater slope, indicating their potential trophic magnification. We assessed health risks from the studied metals using established toxicity reference thresholds. Elevated risks of Hg were identified in three predatory fish species, while other metals and species remain within safe limits. These findings emphasize the significance of foraging patterns in influencing trace metal accumulation in coastal predators and highlight the importance of further monitoring.

Non-breeding movements of the Black-tailed Gull (Larus crassirostris)

With the continued development of tracking technology and increasing interest in animal movement, our understanding of migration behavior has become more comprehensive. However, there are still many species that have not been well studied, particularly sea birds. Here, we present the first year-round Global Positioning System (GPS) tracking data of the Black-tailed Gull (Larus crassirostris) at the population level. We used solar-powered GPS-Global System for Mobile communication (GSM) loggers to successfully track 30 individuals breeding at Xingrentuo Islet, Liaoning Province, China, for 1–3 years. Except for one individual who roamed in the far north of the Yellow Sea during non-breeding period, all others did a directed southward migration. Migration routes and wintering sites differed among migrating gulls and between years for the birds tracked for two or more years. Additionally, during wintering, the migrating gulls were more likely to travel over a large body of water and shift sites, and some trajectories were quite complex, which was probably closely related to what we observed in the field about their boat-chasing behavior. Compared to wintering movements, the post-breeding movements ranged over a smaller area. Specifically, almost all of them had a long post-breeding period near the breeding islet (≥120 days, <220 ​km from the breeding islet), and 80% of the gulls who were tracked more than one year had at least one faithful post-breeding site. Compared to the post-breeding period, only approximately half of the migrating gulls had a pre-breeding period that was shorter (3–20 days) and closer to the breeding islet (≤80 ​km). Migration distance varied among migrating gulls (range 209–2405 ​km) and the gulls moved least distance during post-breeding period. Furthermore, we found that the southward movement of the migrating gulls occurred when the temperature near the breeding islet dropped; specifically, the gulls directly migrated southward away from the post-breeding site. Our results suggest that the Black-tailed Gull has a long post-breeding period but a short pre-breeding period near the breeding islet and high diversity of their migrating patterns (in especial migration routes and wintering sites).

한려해상국립공원 홍도와 태안 난도의 괭이갈매기 번식현황

Seabirds take a long time to recover if their population decreases due to slow growth and small clutch size. This study was conducted to collect basic data of breeding status of Black-tailed gulls (Larus crassirostris) on Hongdo Island of Hallyeohaesang National Park and and Nando Island. These two breeding colonies are designated as natural monuments. We investigated egg volume, clutch size and nest density in May 2022. As results, clutch size was 1.89±0.57 in Hongdo Island and 1.91±0.48 in Nando Island. The egg volume was also similar between Hongdo Island (59.22±5.47) and Nando Island (59.63±3.96). The nest density was significantly higher in Hongdo Island (1.27±0.18/㎡) than in Nando Island(0.54±0.15/㎡). Breeding population was estimated as 56,729 pairs in Hongdo Island while 14,112 pairs in Nando Island based on the proportion of breeding areas. Long-term monitoring is required to know the trends of Black-tailed gulls to protect breeding colonies.

Marine litter pollution of breeding colony and habitat use patterns of Black-tailed gulls in South Korea

Marine litter can affect the survival of the breeding population in seabird colonies. In this study, five 5 m × 5 m quadrats were installed at a Black-tailed gull (Larus crassirostris) breeding colony on Nan Island to collect marine litter and regurgitated pellets, from which the types, sizes, and quantities of marine litter were identified. Global positioning system (GPS) devices were attached to five adult gulls to investigate their major foraging habitats during the breeding period. Eighty-two pieces of marine litter were found, of which 74.4 % were related to fishing; all pellets contained fishing-related marine litter. Over half of the foraging habitats included fishing areas (ports and fish farms). This study is the first to quantitatively demonstrate the exposure of breeding colonies of Black-tailed gulls, the most dominant Korean seabird, to marine litter pollution during the breeding period; the birds forage predominantly in fishing areas close to their breeding colonies during this period.

Spatial distribution and temporal trends of classical and emerging persistent organic pollutants (POPs) in black-tailed gull (Larus crassirostris) eggs from Korea

This study monitored the spatiotemporal trends of persistent organic pollutants (POPs) contamination along the Korean coasts using eggs of the black-tailed gull, a resident bird that occupies a high trophic position in the marine food web. Black-tailed gull eggs were collected from three breeding islands located in the western (Seoman-do), southern (Hong-do), and eastern (Dok-do) seas of Korea during 2015–2019, and egg contents were analyzed for classical and emerging POPs. Among the target analytes, levels of emerging POPs such as brominated flame retardants (BFRs) and perfluoroalkyl acids (PFAAs) were significantly higher in eggs from Seoman-do than other islands. Global positioning system tracking data show that seagulls from Seoman-do traveled frequently to two neighboring major cities (Incheon and Seoul), indicating that the accumulation of BFRs and PFAAs in bird eggs is directly affected by the pollution characteristics of urban areas. Overall, the ratios of PFAA and BFR to the total POPs in eggs from the islands increased over time, while the proportion of classical POPs decreased. A shift from classical POPs to BFRs and PFAAs in seagull eggs was identified. Interestingly, perfluorooctanoic acid (PFOA), which exhibits limited bioaccumulation, was detected at higher levels in eggs from Seoman-do, indicating widespread use of PFOA and maternal transfer to seabird eggs. Continuous monitoring of PFAAs in marine environments of Korea is needed. This study demonstrates that monitoring of seabird eggs is effective for detecting spatial and temporal trends of POPs in the marine environment, and provides insights into emerging POPs such as PFAAs.

Mapping the collision risk between two gull species and offshore wind turbines: Modelling and validation

Promoting the use of renewable energy and conserving biodiversity are conflicting issues that need addressing. While the development of offshore wind facilities/turbines is accelerating, many seabirds have been exposed to collisions with wind turbines. We must identify high collision areas and avoid the construction of wind turbines in these spaces to reduce these conflicts. One solution is to develop useful finer scale sensitivity maps. In this study, we created a fine-scale map of collision risk by spatial modelling using information from bird flights at sea and explored the relative importance of each geographic variable relevant to the risk. Between 2016 and 2019, we collected 3D-location data from 117 black-tailed gulls (Larus crassirostris) of three colonies in two areas and 21 slaty-backed gulls (L. schistisagus) of four colonies in one area of northern Hokkaido, Japan. The spatial models that explain the occurrence of M-zone flight, which is the flight within the heights of high collision risk (20–140 m height), were constructed at a 1 km mesh using a random forest algorithm, a machine-learning tool. The model satisfactory predicted the spatial distribution of M-zone flights using geographic variables and species (correlation coefficient: 0.57–0.94), although data had some degrees of variation between species, years, colonies, and areas. Our model can be applied to other regions, as long as we have general topological information and the locations of colonies and harbors. The distance to the breeding colony and the nearest harbors were important, and the collision risk was 6–7 times higher within 15 km from the colonies and 5 km from harbors. Black-tailed gulls used different sites for foraging and commuting between years, whereas slaty-backed gulls used relatively consistent sites. These variations between species and among years suggest that collecting bird data over multiple years is necessary and effective for creating a generally applicable sensitivity map.

First Report of Habitat Ranges in Black-tailed Gulls (Larus crassirostris) breeding on Hongdo Island, Hallyeohaesang National Park

바닷새의 서식 범위 파악은 개체군 변동을 이해하고 종 보호를 위해 중요하다. 본 연구는 한려해상국립공원 홍도에서 번식하는 괭이갈매기의 연중 서식 범위 파악을 위해 수행되었다. 홍도 괭이갈매기 번식지에서 2018년 괭이갈매기 4개체와 2019년 2개체에 조류위치추적기를 부착하여 위치정보를 수집하였다. 괭이갈매기는 홍도로부터 부산, 거제, 통영, 여수 등 100km 내외의 서식 범위를 이용하였다. 괭이갈매기의 서식 범위는 번식기에 비번식기보다 더 넓었다. 1년 이상 위치를 추적한 성조의 경우 번식기인 5월부터 8월까지는 홍도와 부산, 거제, 통영, 여수 등에 서식했다. 이후에는 남하하여 일본으로 이동한 후 이듬해 2월까지 머물렀다가 3월이 되자 홍도로 다시 되돌아왔다. 본 연구는 한려 해상국립공원 홍도에서 번식하는 괭이갈매기의 서식 범위를 밝힌 첫 논문이다.

Levels and profiles of perfluorinated alkyl acids in liver tissues of birds with different habitat types and trophic levels from an urbanized coastal region of South Korea

Contamination status and characteristics of perfluorinated alkyl acids (PFAAs) including perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonic acids (PFSAs) was examined using liver tissue of birds - black-tailed gulls (Larus crassirostris), domestic pigeons (Columba livia var. domestica), pacific loons (Gavia pacifica), herons (Ardea cinerea), and egrets (Egretta garzetta and Ardea alba) - with different trophic levels, habitat types and migratory behaviors from an industrialized coastal region of South Korea. A wide range of PFAAs (1.09 ng/g to 1060 ng/g; median = 52.6 ng/g) were detected in bird livers from the Korean coasts with high detection frequency. Accumulation features of PFAAs in birds indicated that primarily trophic position and secondly habitat type influence the levels and composition of PFAAs, e.g., relatively high PFAA levels and high composition of odd-numbered long carbon chain PFCAs (perfluoroundecanoic acid (PFUnDA) and perfluorotridecanoic acid (PFTriDA)) and PFOS in higher trophic and marine birds. The prevalence of long carbon chain (≥14) PFCAs likely implies a wide use of fluorotelomer-based substances in Korea. Interspecies comparison in the accumulation profile of persistent organic pollutants (including polychlorinated biphenyls (PCBs), organochlorine pesticides, polybrominated diphenylethers (PBDEs), and PFAAs) reveals relatively high load of PFAAs in inland (pigeons) and estuarine (egrets/herons) species compared to marine bird species, indicating wide use of PFAAs in the terrestrial environment.

Temporal and spatial trends of chlorinated paraffins and organophosphate flame retardants in black-tailed gull (Larus crassirostris) eggs

In this study, eggs of black-tailed gull (Larus crassirostris), a top trophic level predator of marine ecosystem were, for the first time, monitored to assess the temporal and spatial trends of emerging pollutants in South Korea. Two Island regions, namely, Baekryeong-do (Site A) and Hong-do (Site B) were investigated from 2012 to 2018, and the total levels of short chain chlorinated paraffins (SCCPs), medium chain CPs (MCCPs), and organophosphate flame retardants (OPFRs) for both Site A and B were 1180–2931 and 694–2023 ng/g lipid weight (lw), 1287–4898 and 1034–3075 ng/g lw, and 203–499 and 233–409 ng/g lw, respectively. The time-trends of the concentration of pollutants showed an increasing tendency from 2012 to 2018, with the levels predicted to be doubled within three years, following the results of regression analysis. A shift in temporal-trends from shorter to longer chain CPs was noted, suggesting the effect of industrial-related contamination. Especially, significantly high levels of CPs and OPFRs were found in the site adjacent to China, which is reasonable as China is the largest producer and consumer of FRs and plasticizers worldwide. This study is valuable to understand the temporal increment of emerging pollutants as the alternatives of phased-out FRs and plasticizers, while raising the need for continuous environmental management.

Monitoring Breeding Performance of the Black-tailed Gull&lt;i&gt;Larus crassirostris&lt;/i&gt; on Kabushima Island, Japan, from 2012 to 2020

We monitored the breeding performance of Black-tailed Gulls Larus crassirostris on Kabushima Island, which has been connected to Honshu Island by a manmade isthmus since the 1940’s, from 2012 to 2020. The mean number of eggs per nest on 13–20 May between 2014 and 2020 (2.01‒2.16 egg/nest), except for 2019, was higher than that in 2012, 2013, and 2019 (1.57‒1.80 egg/nest). However, the number of chicks on 5–15 July per number of eggs on 13–20 May in 2014 and 2020 (0.01‒0.17 chick/egg) was lower than that in 2012 and 2013 (0.23‒0.29 chick/egg).

Plastic debris ingestion by seabirds on the Korean Peninsula

Plastic ingestion studies in seabirds that analyse the frequency of occurrence and the characteristics of the plastics ingested by each species provide valuable information for marine environmental assessments by quantifying the impacts of marine debris on seabirds. We investigated the frequency of plastic ingestion from a sample of 387 individuals of 11 seabird species on the Korean Peninsula. We found evidence of plastic ingestion in red-breasted mergansers (Mergus serrator) (33.3%), Pacific loons (Gavia pacifica) (10.0%), Swinhoe's storm petrels (Hydrobates monorhis) (93.7%), black-tailed gulls (Larus crassirostris) (12.9%) and ancient murrelets (Synthliboramphus antiquus) (0.9%). In particular, it was observed that Swinhoe's storm petrels had the highest frequency of plastic ingestion, both in terms of the number of affected individuals, and the accumulated mass of plastic debris ingested. The majority of seabirds examined in our study had ingested microplastics, comprised predominantly of user plastics. This is the first report quantifying plastic ingestion in seabirds on the Korean Peninsula and in the broader area of the East Asian Seas.

Per- and polyfluoroalkyl substances and their alternatives in black-tailed gull (Larus crassirostris) eggs from South Korea islands during 2012–2018

The temporal and spatial trends of sixteen per- and polyfluoroalkyl substances (PFAS) and their three alternatives, chlorinated polyfluoroalkyl ether sulfonic acid (F-53B), hexafluoropropylene oxide dimer acid (GenX), and dodecafluoro-3H-4,8-dioxanonanoate (ADONA) in whole eggs of black-tailed gulls from two South Korean islands, Baengnyeongdo (BLD) and Hongdo (HD), were investigated during 2012–2018. A total of 16 analyzed compounds were detected at concentrations of 21.3–47.8 ng/g ww in BLD and 11.2–40.0 ng/g ww in HD. Meanwhile, the mean levels of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were detected at 6.92 ± 4.72 ng/g ww and 0.674 ± 0.993 ng/g ww, respectively. In particular, F-53B, a major alternative to PFOS was detected in each year of the study period with a level of up to 6.66 ng/g ww in all egg samples. Significant increasing temporal trends were observed for PFOS, perfluorononanoic acid (PFNA) and one alternative (F-53B) during the investigated period suggesting continuous use or accumulation of these in the Korean environment. Moreover, distinctive spatial distribution patterns such as a significantly higher F-53B level in HD and an increased PFAS (< C11) in BLD were also observed.

Penguins are competent hosts of Haemoproteus parasites: the first detection of gametocytes, with molecular characterization of Haemoproteus larae

BackgroundThe majority of penguins (Sphenisciformes) have evolved in areas with weak or absent transmission of haemosporidian parasites and are usually naïve to avian haemosporidian infections. Plasmodium parasites are transmitted by mosquitoes, and lethal avian malaria has been often reported in captive penguins in many countries. The related haemosporidian parasites belonging to Haemoproteus and Leucocytozoon have also been detected in penguins but less often than Plasmodium infections. The majority of Haemoproteus infection reports in penguins are based solely on PCR-based diagnostics. It remains unclear if haemoproteids can complete their life-cycle and produce infective stages (gametocytes) in penguins or whether these infections are abortive in penguins, and thus dead ends for transmission. In other words, it remains unknown if penguins are competent hosts for Haemoproteus parasites, which cause disease in non-adapted birds.MethodsTwo captive African penguins (Spheniscus demersus) and two Magellanic penguins (S. magellanicus) were found to be positive for Haemoproteus infection in two open-air aquariums in Japan, and the parasites were investigated using both PCR-based testing and microscopical examination of blood films. Samples from a black-tailed gull (Larus crassirostris) and previously tested gulls were used for comparison.ResultsThe lineage hSPMAG12 was detected, and gametocytes of Haemoproteus sp. were seen in the examined penguins and gull. Observed gametocytes were indistinguishable from those of Haemoproteus larae, which naturally parasitize birds of the genus Larus (Laridae). The detected sequence information and Bayesian phylogenetic analysis supported this conclusion. Additionally, morphologically similar gametocytes and closely related DNA sequences were also found in other gull species in Japan. Phylogenetic analysis based on partial cytb sequences placed the lineage hSPMAG12 of H. larae within the clade of avian haemoproteids which belong to the subgenus Parahaemoproteus, indicating that Culicoides biting midges likely transmit the parasites between penguins and gulls.ConclusionsThis study shows that some species of Haemoproteus parasites complete their development and produce gametocytes in penguins, which may be source of infection for biting midges transmitting haemoproteosis. To prevent haemosporidiosis in zoos, we call for control not only of mosquitoes, but also biting midges.

Parental Birds Incubating Larger Clutches Regulate Their Field Metabolic Rates in Response to Environmental Changes

Species are capable of flexible energy allocation in response to changes in food availability. The extent to which individuals are able to adjust their energy allocation is presumed to be dependent on individual quality. Individuals of lower quality (i.e. better physiological condition) may be at an energy ceiling, and lack the reserves available to be able to expend more energy when environmental conditions deteriorate. Using the doubly labeled water method, we measured the field metabolic rates of free-ranging Black-tailed Gulls Larus crassirostris incubating two- and three-egg clutches during two consecutive years. Lower sea surface temperatures in 2013, compared with those in 2012, provided indirect evidence of poorer food availability in 2013 than in 2012. Parent gulls incubating three-egg clutches were able to increase their energy expenditure, in response to the poor food conditions in 2013, whereas those incubating two-egg clutches were not. Within a gull population we found heterogeneity of the energy allocation process in response to changes in food availability.

Utilization of black-tailed gull (Larus crassirostris) eggs for monitoring of mercury levels in coastal areas of South Korea: Preliminary study

Studies on the monitoring of mercury accumulation using high trophic-level predators of the marine ecosystem have been scarce in South Korea. In this study, we compared the mercury concentrations of the eggs of the black-tailed gulls, a higher-order predator, breeding in two coastal areas. Breeding sites with varying mercury concentrations in land-origin freshwater fish and freshwater and marine sediments were selected in the southeastern (Hongdo Island) and western (Baengnyeongdo Island) seas. The 5-year mean total mercury concentration in eggs collected during the breeding seasons from 2012 to 2016 was higher in those collected from Hongdo than in those collected from Baengnyeongdo. This difference in mercury concentration in eggs was observed for each year. In addition, the total mercury concentration in eggs was consistently higher on Hongdo, which also had higher mercury pollution, than on Baengnyeongdo Island. These results support the suitability of black-tailed gull eggs for monitoring of mercury pollution.