Larus Crassirostris Research Articles

Physical and Chemical Characteristics of Dokdo Soil

To understand the properties of soil in Dokdo, we collected soil samples from 12 locations on Seodo and 23 locations on Dongdo, in Dokdo of Gyeongsangbuk-do Province in 2007-2008 and analyzed the soil's physical and chemical characteristics. Sand comprises the largest component (49.37%) of Dokdo soil, followed by silt (40.70%) and clay (9.93%). The soil structure consists mostly of sand loam, followed by loam and silt loam. The pH level of soils from Dokdo varied dramatically among sampling sites and seasons, ranging from 3.36 to 8.02. The total ion content of Dokdo soil also varies greatly among survey places and periods, but in general the total ion content was high in summer when vegetation develops, and low in spring. The exchangeable cation contents of the soil showed low levels in samples where the soil pH was low, including habitats dominated by Agropyron tsukushiense var. transiens and Echinochloa crus-galli, whereas the exchangeable cation contents were high where the organic contents were high, as in habitats dominated by Liriope platyphylla and Artemisia japonica subsp. littoricola. Soil N contents varied greatly among survey sites and higher N contents were found in soil inhabited by Chenopodiaceous plants than in habitats inhabited by other plants. The substantial differences in phosphorus contents among sites were related to excrement of black-tailed gulls. To understand the basic physical and chemical features of the soil on Dokdo, it will be necessary to conduct seasonal and long-term research on soil pH, ion contents, organic contents, N and P, as well as obtaining precise data from samples collected at different depths.

Avifauna of Geumo Archipelago

A total of 3,248 individuals of 51 species were observed in the Geumo Archipelago (Geumodo, Ando, Yeondo) in Yeosu, Jeollanamdo in two rounds of study conducted from June to September 2008. The dominant species was Larus crassirostris with 1,145 individuals (35.25%) followed by Hirundo rustica with 385 individuals (11.85%), Paradoxornis webbianus with 356 individuals (10.96%), Hypsipetes amaurotis with 219 individuals (6.74%), and Hirundo daurica with 168 individuals (5.17%). Resident birds showed the highest migration of 54.90% followed by summer vagrant birds (31.37%), passage migratory birds (9.8%), winter vagrant birds (1.96%) and vagrant birds (1.96%). The Species biodiversity was 2.43 and the species richness was 6.18.

長崎県雲仙市千々石町におけるホイグリンカモメＬａｒｕｓ ｈｅｕｇｌｉｎｉ，ニシセグロカモメＬ．ｆｕｓｃｕｓ，アイスランドカモメＬ．ｇｌａｕｃｏｉｄｅｓの記録

Since 2002, we have observed gull flocks at Chijiwa Beach in Tachibana Bay, Nagasaki Prefecture, Japan. The gull flocks consist mainly of Black-tailed Gulls Larus crassirostris and Vega Gulls L. vegae. These gulls stay at the beach between October and March. The Vega Gull generally has pinkish legs, but within these flocks some gulls, which look like Vega Gulls, have yellowish legs. Between January 2005 and March 2007 we counted the adult gulls, excluding Black-tailed Gulls and Slaty-backed Gulls L. schistisagus, and calculated the ratio of gulls with yellowish legs in the flocks as being 12.4%. In addition, we attempted to identify these gulls with yellowish legs, using the following characters: body size comparison with Black-tailed Gulls, Vega Gulls or Slaty-backed Gulls; colour of the orbital ring and iris; the dark streaking pattern of head plumage; timing of the moult; mantle colour brightness (Kodak Gray Scale: GS); wing projection (Fig. 1: C); and wingtip pattern. In late January 2006 and 2007, and late February 2007, we selected three gulls and photographed them. Based on the respective combination of the characters listed above we identified one as L. heuglini heuglini, another as L. fuscus graellsii/intermedius, and the third as L. glaucoides kumlieni. Given that gulls with yellowish legs comprise 12.4% of the gulls at the beach, it seems probable that gulls related to the Vega Gull, such as L. heuglini and L. fuscus, more frequently migrate in the winter period than had hitherto been believed.

Hydroxylated polychlorinated biphenyls (OH-PCBs) in the blood of mammals and birds from Japan: Lower chlorinated OH-PCBs and profiles

An analytical method was developed to measure tri- to octa-chlorinated OH-PCBs and pentachlorophenol (PCP) in the whole blood. Further, baseline data on the levels and profiles of these phenolic compounds in Japanese mammals (human, cat, dog, raccoon dog, and northern fur seal) and birds (black-tailed gull, common cormorant, and jungle crow) were obtained. Eighteen identifiable and fifty unknown peaks of OH-PCBs were detected and the major congeners identified were 4′OH-CB101/120, 4OH-CB107/4′OH-CB108, 4OH-CB146, 4OH-CB178, 4OH-CB187, 4′OH-CB172, 4OH-CB202, and 4′OH-CB199. Relatively higher concentrations of OH-PCBs were found in animal species than humans; OH-PCB levels in dog, raccoon dog, black-tailed gull, and common cormorant blood were one order of magnitude higher than in humans. Penta- to hepta-chlorinated OH-PCB congeners were predominant in human blood, but profiles of OH-PCBs in other animals widely varied by species. Elevated composition of tri- and tetra-chlorinated OH-PCBs in cat blood and octa-chlorinated OH-PCBs in dog and raccoon dog blood were observed. In cat blood, elevated PCP concentration was also found. When concentration ratios of OH-PCBs to PCBs were calculated in all the animal blood, the ratios in dog, raccoon dog, and cat were notably higher than in other species. These results indicate that animals other than humans, especially cat and canine species such as dog and raccoon dog, might be at risk from OH-PCBs.

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.

Habitat Selection by Black-tailed Gulls on Hongdo Island, Korea

Habitat selection in Black-tailed Gulls (Larus crassirostris) on Hongdo Island, Korea, was studied during the breeding period in 2002-2003. To compare topographical advantages and disadvantages on breeding, we examined two habitats on the island: rocky-cliffs (lower and edge) and grassy (upper and inside) for differences in breeding biology and feeding frequency. In rocky-cliff habitat, Black-tailed Gulls had higher clutch size, faster laying and hatching date, and higher hatching and fledging success. Topographically, rocky-cliff habitat had two advantages-it was closer to sea and difficult to access. Proximity to the sea allowed higher feeding frequency whereas difficult access restricted predators. Conversely, grassy habitat was farther from the sea and allowed easier access to predators, but a lot of grass covered nests to protect eggs and chicks. These disadvantages caused low feeding frequency and higher hatching failure. Egging by fisherman was also a disadvantage of grassy habitat because of easy access from landing places. Therefore, our results suggested that rocky-cliff habitat was more profitable habitat than grassy habitat and this profitability was related to topographical difference between habitats.

Avifauna of Mara Island, Korea

As results of this study, it was found that the total species observed in Mara-island was 126 species, including 43 species and 1,338 individuals at the 1st observance, 10 species and 5,080 individuals at the 2nd observance, 27 species and 472 individuals at the 3rd observance, 90 species and 913 individuals at the 4th observance, and 29 species and 268 individuals at the 5th observance respectively. In terms of migration types of birds, it was found that sedentary birds were 26 species, winter migratory birds were 14 species, summer migratory birds were 32 species, passage migrant birds were 40 species, vagrants were 14 species, and birds breeding in the main island of Jeju and Mara island were 58 species. In terms of dominance, it was found that Larus argentatus was at minimum 5,000 individuals (69.07%), Calonectris leucomelas was 1,000 individuals (13.81%), and each of Hirundo rustica and Emberiza pusilla was 120 individuals (1.66%) (Table 1). On the observed number basis, the number of species certified one individual a time was 45 species, the species certified 2 individuals a time was 20 species, 3~100 individuals a time was 53 species, and over 100 individuals a time was 7 species such as Calonectris leucomelas, Larus argentatus, Larus crassirostris, Hirundo rustica, Emberiza pusilla Pallas, Phylloscopus occipitalis, and Apus pacificus. The species newly recorded in Jeju island from this study were 7 species totally, and among them, 2 species such as Phylloscopus fuscatus, and Acrocephalus aedonin were found in 2006 and 5 species such as Sula leucogaster, Locustella ochotensis, Erithacus svecicus, Oenanthe pleschanka, and Phylloscopus proregulus were found in 2007.

Effect of interannual variations in sea-surface temperature on egg-laying parameters of black-tailed gulls (Larus crassirostris) at Teuri Island, Japan

Sea-surface temperature (SST) directly and indirectly affects the distribution and abundance of prey species for seabirds, so we expect variation in SST to be associated with variation in seabird life history traits. In black-tailed gulls (Larus crassirostris) at Teuri Island in northern Hokkaido, Japan, we investigated the diet of the gulls prior to egg laying in 2004 and 2005, and examined the influences of SST in March or April, when the gulls congregate in the colony, on egg-laying parameters using 13 years of data (1992–2004). The gulls fed on krill (Thysanoessa inermis) and fish prior to the egg laying. Mean first egg dates and clutch sizes were significantly and quadratically related to SST anomalies in March, but were not influenced by SST anomalies in April. There was no significant effect of SSTs in either March or April on egg volume. Sea-surface temperature anomalies in March of the years of early laying (−1 to 1°C) were higher than those in 2001 (−2.2°C), but lower than those in 1992 (+1.2°C) and 2004 (+1.1°C). Thysanoessa inermis congregates to spawn at the sea surface, when SSTs rise 3−4°C. Thus, a mismatch between food availability and the timing of egg production in the gulls could have occurred in these 3 years. This study suggests that SST fluctuations prior to laying are important in breeding success of black-tailed gulls.

Avifauna of Baengnyeongdo Island

Birds observed in Baekryeongdo from Oct. 18 to Oct. 20, 2007 were 4503 individuals in 11 orders, 28 families, and 59 species. The most dominant species was Anas poecilorhyncha (1721 individuals) representing 38.22%, followed by Anser fabalis (859 individuals) with 19.08%, Larus crassirostris (232 individuals) with 5.15%, Aegithalos caudatus caudatus (193 inviduals) with 4.29%, and Aythya fuligula (157 individuals) with 3.49%. The species diversity (H') was highest, 2.61, in D area where the species richness (Da) was lowest. Species richness (Da) was 4.54 in E area and 4.38 in A area while species diversity (H') was lowest, 1.77 in E area and 1.76 in A area. This study found 9 species that were legally protected.

Anti-Predator Responses of the Black-tailed Gull (Larus crassirostris) Flock to Mobbing and Mew Call Playbacks

We studied the functional roles of two types of calls, mew calls and mobbing calls, of the black-tailed gull (Larus crassirostris) by examining responses of mixed flocks of gulls to the playback calls. Playback experiments were conducted on four days between 11 May and 5 June 2007 at 16 sites in Sinjindo-ri and Dowhang-ri, Taean-gun, Chungnam province and Imjado, Sinan-gun, Jeonnam province, South Korea. We examined the anti-predator responses of the gulls to the playback trials. We found that gull flocks initially responded to mew call playbacks by mobbing in less than half of playback trials (6/14) while all trials involving playbacks of the mobbing call and control (group mobbing) call evoked mobbing. When trials in which no response was recorded were excluded, we found that the gulls' responses to mobbing and group mobbing call playbacks was more intense than their response to mew call playbacks, in that gulls mobbed longer, more gulls responded, and gulls took flight after a shorter time interval. However, the intensity of the gulls' response did not differ in mobbing call and group mobbing call playbacks. The results of this study suggest that the mixed-species flocks of gulls discriminate between the mew calls and the mobbing calls.

抱卵期におけるウミネコの血漿テストステロン濃度

In some avian species, male plasma testosterone levels are maximum during the courtship or copulation periods, but decline abruptly once incubation starts. However, testosterone levels of male Black-tailed Gulls Larus crassirostris during the course of breeding remain unknown. In 2006, blood samples of 23 incubating males were collected at Rishiri Island, Hokkaido, Japan and testosterone was measured by enzyme immunoassay kit. Plasma testosterone level (mean±S.E.: 0.737±0.282 ng/ml) was assumed to decline with elapsed days from the onset of incubation, as shown in other species.

Anti-Predator Responses of Black-Tailed Gull (Larus crassirostris) Flocks to Alarm Calls during the Post-Breeding Season

Black-tailed gulls (Larus crassirostris) produce alarm calls apparently related to their anti-predator behaviors, but the hypothesis that the calls are actually used as functionally referential alarm signals has not yet been tested. In this study, we performed a series of experiments using visual (a stuffed goshawk: Accipiter gentilis) and acoustic (alarm calls and a control vocalization) stimuli at 15 sites in Sinjindo-ri and Dowhang-ri, Taean-gun, Chungnam province to examine anti-predator responses of the gulls to alarm calls in playback trials. We found that the gulls` visual recognition of a perched hawk model in the absence of alarm vocalizations was weak or absent because the model was noticed in only two out of 16 trials. The gulls` responses to playbacks of the alarm call only and the alarm call with a visual stimulus differed from responses to the control vocalization in latency to approach, time mobbing, and the percentage of gulls responding, while the responses to alarm call only differed from alarm call with a visual stimulus in latency to first fly, latency to call, and time mobbing. The results of this study suggest that alarm calls of black-tailed gulls are used to elicit appropriate anti-predator behaviors that are intensified when a predator is detected visually.

Factors affecting egg predation in Black‐tailed Gulls

AbstractIn colonial seabirds, nesting density, egg‐laying date and nest microhabitat affect the probability of eggs being taken by avian predators. Jungle Crows (Corvus macrorhynchos) are dominant predators of eggs of Black‐tailed Gulls (Larus crassirostris). Factors affecting the probability of gulls allowing the crows to attack their nests or depredate their eggs and the probability of eggs being taken were studied by direct observation and egg census, respectively. The effect of vegetation heights, position in the colony, egg‐laying date and neighbour nests on the probability of eggs being taken were examined at multiple spatial scales. Gull nests were depredated more easily by larger groups of crows. Nests in peripheral areas (<4 m from the edge of the colony) were also depredated more easily by the crows walking on the ground. Although the nests where eggs were laid early in the season were depredated more frequently, such nests highly synchronised in egg laying within a <2‐m radius were less likely to be depredated than less‐synchronised nests. The nests in tall vegetation were less likely to be depredated though those having neighbour nests in tall vegetation were not. The number of neighbour nests did not affect the probability of eggs being taken. Antipredation effects of nesting microhabitats vary with spatial scales at which the crows search and attack the nests of gulls.

Sea and colonial-nesting birds of islands in the southern part of Amurskii Liman

The quantity of the nesting couples of sea birds on the islands of the southern part of Amurskii Liman was determined: common heron Ardea cinerea, slaty-backed gull Larus schistisagus, black-tailed gull L. crassirostris, and sooty guillemot Cepphus carbo.

Evaluation of environmental factors to predict breeding success of Black-tailed Gulls

This study demonstrated prediction of breeding success of Black-tailed Gulls in relation to the selected environmental factors through evaluation of relative importance in determining breeding success. The data were obtained from the 258 selected and 120 non-selected sites for breeding of the gulls during the breeding periods in 2002–2003. Breeding success at the selected sites, and environmental factors such as vegetation cover, vegetation height, rock cover, nest-wall, nearest distance between neighbors and slope, were measured at each sampling site. For predicting breeding success of Black-tailed Gulls, we used two different artificial neural networks in this study: self-organizing map (SOM) and multilayer perceptron (MLP). SOM was used to classify the sampling sites based on the environmental factors, whereas MLP was implemented to prediction of breeding success of the gulls at the non-selected sites based on environmental conditions. In our results, SOM discriminated clearly the sampling sites and presented differences in environmental factors between the selected and non-selected sites. Subsequently, the breeding success was accordingly predicted by MLP. Nest-wall was considered the most important environmental factor in determining survival status of the gulls. An increase in nest-wall and vegetation cover was required to support breeding of the specimens for managing the habitats for Black-tailed Gulls.

남해 연안의 홍도에서 집단 번식하는 괭이갈매기의 한배 알 수와 번식 성공률

We studied variation in clutch size, hatching, fledging and breeding success of the Black-tailed Gull (larus crassirostris) at Hongdo Island, which supported the largest breeding colony of the species, in South Korea in 1997 and 2000 to 2003. Cluck size was recorded in 1,388 nests and breeding success was estimated in 83 nests. Mean clutch size was 1.89 t 0.65. A total of 63.9% of the eggs hatched and 53.5% of the chicks survived until fledged. Breeding success was 34.2%. Causes of breeding failure were eggs missing (14.9%), rotten eggs (15.5%) and predation (2.4%) during the incubation period and chicks missing(35.8%), starvation (7.4%) and pecked chicks (3.2%) during the chick rearing period. In 2002, the main causes of breeding failure were eggs missing (17.2%) and rotten eggs (6.9%) during the incubation period and missing chicks (15.5%), starvation (3.5%) and pecked chicks (6.9%) during the chick rearing period. Most chick mortality occurred within three days after hatching.

The Relationship between Vegetation Cover and Hatching Success, and Chicks' Survival in Black-Tailed Gulls on Hongdo Island

During the breeding seasons in 2002 and 2003, the influences of vegetation cover on breeding processes of Black-tailed Gulls (Laurs crassirostris) were studied on Hongdo Island. We checked dutch sizes, calculated hatching success and survival rates on day 15 and a vegetation cover, There was significant positive relationship between vegetation cover and hatching success, and survival on day 15. In order to analyze the relationship, sample nests were categorized as 'exposed' and 'covered' nests, and the breeding processes at each nest were compared. Hatching success and survival on day 15 in covered nests were significantly higher than ones in exposed nests. However, in clutch size, there was no significant difference. The rate of the hatching and survival failure was different amongst the categorized nests. The primary cause of hatching failure in covered and exposed nests was 'disappeared', and the primary causes of survival failure on day 15 were 'disappeared' and 'killed by adults'. The failure in exposed nests was significantly larger than that of covered nests. In the breeding of Black-tailed Gulls on Hongdo Island, vegetation cover influenced the survival of eggs and chicks as the cover provided shelter against predators and extreme weather.

Multivariate analysis and self-organizing mapping applied to analysis of nest-site selection in Black-tailed Gulls

The factors affecting nest-site selection and breeding success of Black-tailed Gulls ( Larus crassirostris) were studied in Hongdo Island in Korea during the breeding seasons in 2002 and 2003. Two analyzing methods, Principal Component Analysis (PCA) and Self-Organizing Map (SOM) – an unsupervised learning method in artificial neural networks, were applied to multivariable datasets characterizing nest-sites of the gulls. Both methods provided insights on the major trends in nest-site selection by Black-tailed Gulls. PCA showed that the variables regarding the “wall” effect such as rock cover and nest-wall (positively), and the nearest distance between neighbors (negatively) were related to breeding success of Black-tailed Gulls. SOM confirmed ordination of the sample sites by PCA and efficiently classified nest-sites according to environmental condition for breeding. Grouping based on the “wall” effect on PCA was more finely revealed in subdivision on SOM regarding the variables of slope and the nearest distance between neighbors. The use of techniques in ecological informatics such as SOM would be an efficient tool in analyzing data for breeding behavior of birds.

Body distribution of trace elements in black‐tailed gulls from Rishiri Island, Japan: Age‐dependent accumulation and transfer to feathers and eggs

Body distribution and maternal transfer of 18 trace elements (V, Cr, Mn, Co, Cu, Zn, Se, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Hg, Tl, and Pb) to eggs were examined in black-tailed gulls (Larus crassirostris), which were culled in Rishiri Island, Hokkaido Prefecture, Japan. Manganese, Cu, Rb, Mo, and Cd showed the highest levels in liver and kidney, Ag, Sb, and Hg in feather, and V, Sr, and Pb in bone. Maternal transfer rates of trace elements ranged from 0.8% (Cd) to as much as 65% (Tl) of maternal body burden. Large amounts of Sr, Ba, and Tl were transferred to the eggs, though maternal transfer rates of V, Cd, Hg, and Pb were substantially low. It also was observed that Rb, Sr, Cd, Cs, and Ba hardly were excreted into feathers. Concentrations of Co in liver, Ba in liver and kidney, and Mo in liver increased significantly with age, whereas Se in bone and kidney, Hg in kidney, and Cr in feather decreased with age in the known-aged black-tailed gulls (2-20 years old). It also was suggested that feathers might be useful to estimate contamination status of trace elements in birds, especially for Hg on a population basis, although the utility is limited on an individual basis for the black-tailed gulls. To our knowledge, this is the first report on the maternal transfer rate of multielements and also on the usefulness of feathers to estimate contamination status of Hg in birds on a population basis.

Incubation capacity limits maximum clutch size in black‐tailed gulls Larus crassirostris

Factors determining clutch size of birds have long been the central issue in studies in life histories. It is assumed that the configuration of brood patches could limit the maximum clutch size. To test this hypothesis we manipulated clutch sizes and measured egg temperature as well as reproductive consequences in black‐tailed gulls Larus crassirostris, which usually lay two egg clutches and have three brood patches. Mean egg temperature in 4‐egg clutches (32.6±1.0°C) was significantly lower than in 2‐egg (34.6±0.4°C) and 3‐egg clutches (34.1±0.4°C), because egg temperature of the coolest egg within a 4‐egg clutch was often substantially lower than the other three eggs. The proportion of eggs hatching from 4‐egg clutches (11.6%) was lower than those of 2‐egg (49.1%) and 3‐egg clutches (52.0%). Four‐egg clutches had longer incubation periods (29.6±1.3 day) than 2‐egg (28.1±1.7 day) and 3‐egg clutches (28.0 ±1.3 day). The results indicate that incubation capacity, which may be determined by the configuration of brood patches, limits the maximum clutch size in black tailed gulls, but not the actual clutch size typically laid.