Breeding population abundance such as colony size of seabirds is not generally considered to be particularly sensitive to the annual dynamics of the food conditions because of the long life-span and high adult survival rate. However, in seabird species in which adults decide to breed or not depending on the food conditions, population abundance can respond sensitively to the annual variation in the food conditions. Here, we examine the effects of the regional annual stock abundance of Japanese Sand Lance Ammodytes personatus, and their local temporal availability during the egg-laying period on the size of a Black-tailed Gull Larus crassirostris and Slaty-backed Gull L. schistisagus, breeding colony over 12 years on Rishiri Island, northern Japan. The total number of nests of both gull species increased significantly with the regional annual stock abundance, but not with the local temporal availability of the sand lance. The number of Black-tailed Gull nests without eggs was significantly higher in the year with lower local temporal availability indicating that more Black-tailed Gull parents gave up egg-laying after nest building. Colony size in these species can be a useful indicator reflecting local food conditions.

Large amounts of marine-derived nitrogen are carried ashore by seabirds in their feces (ornithogenic N). Various topological, meteorological; and environmental factors can affect microbial transformation of ornithogenic N altering the physical and biochemical conditions of the soils. Tsunami may be a factor affecting ornithgenic soil N dynamics leading to changes in soil conditions. We examined the effects of the tsunami triggered by the 11 March 2011 earthquake off the East Coast of Honshu. Japan, on ornithogenic soil N in the Black-tailed Gull Larus crassirostris breeding colony on Kabushima (Kabu Island) four months after the disaster. There were no differences in the total N content in soils between tsunami splashed (upper half of the island) and flooded areas (lower half), and the visual topographv was comparable to that reported before the tsunami. It seems that the tsunami may not have extensively removed accumulated omitliogenic N in the soils, nor did it induce deposition of organic matter derived from marine sediments. However, delta N-15 values of soil N were lower in the area flooded by the tsunami than in the splashed area, suggesting the possibility that the tsunami caused leaching of ornithogenic N from the soil. Soils flooded by the tsunami contained higher levels of marine salts than those from the splashed area. N isotopic differences between NH4- and NO3-N were smaller in the flooded soils than in the splashed area. This indicates that nitrification of ornithogenic soil N is suppressed in the flooded area because of the remarkable increase in the salt concentration of the soil.

Avian ecological functions can provide ecosystem service benefits to humans. Although the values of avian provisioning and cultural services are well understood, the values of supporting and regulating services are not. Through predation, transportation, and excretion, birds play various roles in terms of seed dispersal/pollination, controlling prey species populations, scavenging, and nutrient cycling. These behaviours provide benefits contributing to increased agricultural productivity, pest control, and habitat creation/maintenance for humans. Though attempts have been made recently to evaluate the economic significance of avian ecosystem services, such attempts remain scarce. In Japan, where people have traditionally enjoyed avian ecosystem services mainly in terms of their support of agricultural ecosystems, an understanding and evaluation of the value of avian ecosystem services is essential.

The assimilation efficiency and growth of Rhinoceros Auklet Cerorhinca monocerata chicks (30-35 age of days) fed with Japanese Sand Lance Ammodytes personatus and Antarctic Krill Euphausia superba were investigated. Chicks were fed 79.4 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn; <clig:><cotfcalt:><calgf:>3.1 gwet /d (mean <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn; <clig:><cotfcalt:><calgf:>SD) of sand lance, which included 497.2 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn; <clig:><cotfcalt:><calgf:>14.9 kJ energy, 4.3 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn; <clig:><cotfcalt:><calgf:>0.2 g lipid, and 12.3 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn; <clig:><cotfcalt:><calgf:>0.5 g protein. Chicks were fed 129.3 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn; <clig:><cotfcalt:><calgf:>2.7 gwet /d krill, which include 746.8 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn;<clig:><cotfcalt:><calgf:>15.5 kJ energy, 3.1 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn;<clig:><cotfcalt:><calgf:>0.1 g lipid, and 23.3 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn;<clig:><cotfcalt:><calgf:>0.5 g protein. The assimilation efficiency (corrected with nitrogen retention) of the sand lance-fed chicks (82.8 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn;<clig:><cotfcalt:><calgf:>0.5%) was significantly higher than the krill-fed chicks (76.6 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn;<clig:><cotfcalt:><calgf:>0.6%). During the experiment, daily mass increments of the sand lance-fed chicks were 11.0 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn;<clig:><cotfcalt:><calgf:>4.7 (g/d, n=12) and of the krill-fed chicks 9.7 <clig:0><cotfcalt:0><calgf:ProportionalWidthForm>&plusmn;<clig:><cotfcalt:><calgf:>2.7 (g/d, n=14). Sand lance-fed chicks gained body mass significantly faster than did krill-fed chicks after controlling for the significant age effect. Krill may be inadequate for chick growth of the auklets due to the poorer lipid content, compared with sand lance.

We measured the nutritional composition and energetic values of 19 prey species of Great Cormorants Phalacrocorax carbo in Chubu, central Japan. Samples were collected during 2005–2012 from several breeding colonies, fish markets, rivers, and the sea near colonies. Lipid content and energetic value (dry mass based) varied widely, from 0.6% and 12.43 kJ/g for red swamp crayfish Procambarus clarkii to 38.2% and 27.79 kJ/g for white-spotted conger Conger myriaster.

Planktivorous alcid females feeding more on lower trophic prey, i.e. copepods, during the pre-breeding season, lay larger eggs. The Rhinoceros Auklet (Cerorhinca monocerata) is piscivorous, but feeds also on krill in the spring at Teuri Island, Hokkaido, Japan. To examine the factors affecting their egg volume, we measured body size, body condition and the nitrogen stable isotope ratio (&delta;¹⁵N, a proxy of trophic level TL) of blood and feathers of male and female parents incubating eggs in three years (2010, 2011 and 2012). In 2011 and 2012, we sampled eggs within one day of laying and measured &delta;¹⁵N and &delta;¹³C (carbon stable isotope ratio) of yolk, albumen and membrane and those of feathers and blood of the female parents. We also sampled stomach contents of adults using water off-loading technique during the laying and incubation period, and determined their prey composition. Female body condition and size as well as male body size positively affected the egg volume index. Birds fed on low (krill) and high (fish) trophic prey during the laying and incubation periods, while individual variation in the &delta;¹⁵N of blood cells that reflected TL during the pre-laying period did not affect the egg volume index. &delta;¹⁵N of breast feathers that reflected TL during the molting period also did not relate to egg volume index. &delta;¹⁵N and &delta;¹³C of feathers and blood of females did not correlate with those of egg yolk, albumen, or egg membrane.

Long-lived animals sometimes skip one or more breeding seasons; however, little is known about their movements and activities during such sabbatical' periods. Here we present novel data on year-round movements and activities of two male black-tailed gulls Larus crassirostris during a sabbatical year. We compare the data with those in a year when they bred and with those of two other breeding males. The year-round migration routes of two sabbatical males were consistent with those of the breeding males: they returned to the breeding area but did not visit the colony in the sabbatical year. They landed more frequently on water (a potential index of foraging effort) during the non-breeding autumn and winter prior to the sabbatical year than before breeding. Sabbatical gulls may forage more intensively to recover body condition immediately after breeding.

Environmental factors affecting the capture rate of the Japanese water shrew Chimarrogale platycephala were investigated in the Kamikoshi River, Aichi, central Japan, from June to December in 2011. The shrews were significantly more frequently captured at confluences and in narrow secondary tributaries not shown on the 1/25,000 scale topographical map published by the Geographical Survey Institute. They were also more frequently captured within three days after heavy rainfall (over 150 mm/day). Soil inflow into the tributaries caused by pavement construction projects did not affect capture rate.<br>

Few studies have been made so far of inter-colonial and annual variation in the diet of breeding Great Cormorants Phalacrocorax carbo. We investigated their diet during the chick rearing period by collecting regurgitates from five breeding colonies, in the Chubu area, central Japan, in 2009-2011. Those cormorants breeding in coastal colonies took mainly Flathead Mullet Mugil cephalus cephalus and Dotted Gizzard Shad Konosirus punctatus, while those breeding in inland colonies took a wide range of fishes in any given year. The frequency of introduced Red Swamp Crayfish Procambarus clarkii and native Oriental River Prawn Macrobrachium nipponense in the diet increased in years when frequencies of fishes decreased, at both inland and coastal colonies.

Daily food intake and changes in body mass of five, hand-reared sub-adult Great Cormorants Phalacrocorax carbo hanedae were measured in an outdoor cage over 117 days during winter and spring. During the period of the study, the five birds maintained almost constant body masses, despite variation in their daily food intake (they were fed ad lib). Daily food intake mass per unit body mass of individuals decreased significantly as the ambient air temperature increased, but daily body mass increment per unit body mass of individuals did not. These results indicate that the daily energy expenditure of cormorants decreases as ambient air temperature increases, probably because of the suppression of thermoregulation costs.

Terrestrial ecosystems near breeding/roosting colonies of piscivorous seabirds can receive a large amount of marine-derived N in the form of bird feces. It has been well demonstrated that N input from seabirds strongly affects plant communities in forests or coastal grasslands. The effects of nutrient input on plant communities in agricultural ecosystems near seabird colonies, however, have rarely been evaluated. This relationship was examined in rice-paddy fields irrigated by a pond system located near a colony of the Great Cormorant Phalacrocorax carbo in Aichi, central Japan. In the present study, spatial variations in N content (N %) and N stable isotope composition (δ15N) of soils and wild grass species together with the growth height of plants in paddy fields in early spring (fallow period) were examined. Soils had a higher N % and δ15N values in fields associated with an irrigation pond that had N input from cormorants. The δ15N values tended to be higher around the inlet of irrigation waters, relative to the outlet. These results indicate that cormorant-derived N was input into the paddy fields via the irrigation systems. Plants growing in soil with higher δ15N had higher δ15N in the above-ground part of the plants and had luxurious growth. A positive correlation in plant height and δ15N of NO3-N was observed in soil plough horizons. © 2012 Elsevier Ltd.

To understand the adaptive significance of colonial breeding, evaluating the costs and benefits that colonial breeding provides to individuals is necessary. To study some of these costs and benefits of colonial breeding, over 24,000 nest-hour observations of kleptoparasitism (stealing of food being fed to young), intraspecific attacks on and killing of chicks; and chick adoption were conducted in colonial breeding Black-tailed Gulls (Larus crassirostris) during two breeding seasons. Although kleptoparasitism was rarely observed (under 0.001 events/nest/observational hour), the occurrence of chick-attacks was 5-10 times higher (0.005-0.01 events/nest/observational hour) than that of kleptoparasitism, with over 10% of the attacks resulting in the death or disappearance of chicks. More than 60% of all attacks on chicks were by failed breeders and non-breeding adult floaters. The survival of attacked chicks reached 98-100% if they escaped into other nests and were accepted by "foster" adults, or if they were defended by non-parental,adults. Chick adoption and non-parental defense were more likely to be observed among breeding neighbors (52-60% of chick adoptions and almost all examples of non-parental defense) than among non-neighbors. An increased chick survival rate, resulting from nesting in close to proximity to conspecific neighbors, was considered as a factor promoting colonial breeding among the Laridae. Received 20 January 2012, accepted 5 August 2012.

Carbon and nitrogen stable-isotope ratios were measured in the egg yolks of four species of seabirds in Teuri Island and Rishiri Island, Japan. Delta N-15 of the yolks of Rhinoceros Auklets Cerorhinca monocerata (11.2-12.3 parts per thousand) and Black-tailed Gulls Larus crassirostris (11.3-12.5 parts per thousand) were lower than those of Slaty-backed Gulls Larus schistisagus (13.4-14.2%0) and Japanese Cormorants Phalacrocorax capillatus (14.0-16.2 parts per thousand); suggesting that the former two species foraged mainly on low trophic level small fishes and sometimes on krill, while the latter two species fed on higher trophic level prey and larger fishes.

Individual behaviors of animals do not evolve separately; they do so in association with other behaviors caused by single shared genetic or physiological constraints and/or favored by selection. Thus, measuring behavioral syndromes-suites of correlated behaviors across different contexts-leads to a better understanding of the adaptive significance of variations in behaviors. However, relatively few studies have examined behavioral syndromes in wild animal populations in changing environments. We investigated a potential behavioral syndrome across antipredator nest defense, territorial defense, chick provisioning, and mating behaviors of male Black-tailed Gulls Larus crassirostris in two successive years under different conspecific territorial intrusion risks and food conditions. Males that presented high levels of antipredator nest defense (aggressive antipredator defenders) against a crow decoy (crows are egg predators) defended their territories against conspecific intruders more frequently than did other males (nonaggressive antipredator defenders), independent of the risk of intrusion. Aggressive antipredator defenders also fed their chicks more frequently than nonaggressive males, but only in a year of low food availability. Taken together, this indicates that males show consistent aggressiveness regardless of breeding context (antipredator and territorial defense), but can regulate food provisioning according to food availability.

In some bird species, the survival of chicks hatching later in the season is lower than those hatched earlier due to increased risk of predation and a seasonal decline in feeding conditions. To reduce these risks, it might be advantageous for late-hatched chicks to grow faster and hence fledge at younger age. In this experimental study, the growth rates of early- and late-hatched Rhinoceros Auklet Cerorhinca monocerata chicks were compared under average and poor food supplies in captivity. Controlling for potentially confounding effects of chick mass at 10 days old, chick age and nest-chamber temperature, late-hatched chicks had higher wing growth rate than early-hatched chicks before attaining the minimum wing length required for fledgling under both average and poor food supplies. After attaining the minimum wing length, however, late-hatched chicks had a lower fledging mass, indicating a potential cost that could diminish the early advantage of fast wing growth.

Offshore wind-power generation is one of the fastest growing industries in many areas, especially Europe. Offshore wind farms (OWFs) can provide several economic benefits, but are potential threats to some marine organisms. Noises produced by exploration drilling and pile-driving during construction of OWFs can impede acoustic communication of fishes and marine mammals. Wind turbine bases with scour protection structures directly reduce the habitats of marine organisms and potentially affect their survival by altering oceanographic conditions and food availability. Collisions between turbines and flying birds have also been frequently observed at OWFs. Foraging seabirds and/or migratory terrestrial birds display avoidance responses to OWFs (e.g. detour flights around the turbines), and several researchers have modelled the additional energetic costs of such detour flights and potential impacts on the body condition of the birds. Further long-term studies are needed for various organisms at OWFs across a broad geographic distribution. Efforts to mitigate the impacts of OWFs on marine ecosystems should include the avoidance of OWF construction in areas harbouring important foraging areas and migratory routes, acoustic deterrence methods (e.g. bubble curtain) during construction, and turning off turbines during breeding and migrating seasons.

The physiological state of parent birds combined with the value of their clutch may affect the intensity of their nest defense. In colonially breeding birds, nest-defense intensity may also be affected by the behavior of neighbors. We investigated individual variation in the nest-defense intensity among colonial Black-tailed Gulls (Larus crassirostris Vieillot, 1818) over 2 years. Only 30%-40% of males attacked a decoy of an egg predator (Large-billed Crow (Corvus macrorhynchos Wagler, 1827)), and the other males and females rarely attacked. Males attacking the decoy had higher levels of plasma testosterone than males that did not attack. Each male&apos;s, but not female&apos;s, nest-defense intensity was consistent throughout the incubation period and also across years. The intensity was not related to egg-laying date, clutch size, or age of offspring. The intensity was likely to be higher when individuals had one or more neighbors, representing higher nest-defense intensity in the year where gulls had larger number of adjacent neighboring nests (5.23 nests), but this trend was not observed in the year where they had smaller number of the neighboring nests (3.73 nests). Thus, in addition to testosterone levels, behavior of neighbors also influences the nest-defense intensity.

Seabirds and large fishes are important top predators in marine ecosystems, but few studies have explored the potential for competition between these groups. This study investigates the relationship between an observed biennial change of pink salmon (Oncorhynchus gorbuscha) biomass in the central Bering Sea (23 times greater in odd-numbered than in even-numbered years) and the body condition and diet of the short-tailed shearwater (Puffinus tenuirostris) that spends the post-breeding season there. Samples were collected with research gill nets over seven summers. Both species feed on krill, small fishes and squid. Although the mean pink salmon catch per unit effort (in mass) over the study region was not related significantly with shearwater&apos;s stomach content mass or prey composition, the pink salmon biomass showed a negative and significant relationship with the shearwater&apos;s body mass and liver mass (proxies of energy reserve). We interpret these results as evidence that fishes can negatively affect mean prey intake of seabirds if they feed on a shared prey in the pelagic ecosystem.

Testosterone affects male sexual-, aggressive-, and parental-behaviors in bird species. To understand the breadth of the proximate contribution of testosterone to breeding behaviors in male Black-tailed Gulls Larus crassirostris, sexual behaviors, aggressive behaviors against egg-predators and conspecifics, and chick-provisioning behavior of five testosterone-implanted males (T-males) were observed and compared with those of three control males (placebo-implanted; C-males). T-males showed significantly higher levels of courtship and copulation behaviors than C-males. The levels of aggressiveness against egg-predators and against conspecifics, and the rate of feeding of chicks did not differ between T- and C-males. These results suggest that sexual and mating behaviors in male Black-tailed Gulls may be affected by testosterone, while aggressive- and feeding-behaviors are affected by certain ecological factors, such as individual age, or a necessity for high levels of feeding by males, rather than by testosterone.

Mother birds can enhance growth and/or survival of chicks by supplying energetic and hormonal resources to the egg yolk (i.e. maternal effect). In several bird species, mothers supply higher level of testosterone to the eggs laid later within the clutch and enhance the growth of the chick to compensate for the disadvantage of the later hatching. As same as this within-clutch mechanism, mothers breeding later in the season can be expected to supply higher level of testosterone to the clutch. However, among-clutch seasonal variation in yolk testosterone levels has been rarely described. Here, we investigated among-clutch seasonal variation in the yolk testosterone level in Black-tailed Gulls Larus crassirostris, as well as within-clutch variation. Mean yolk testosterone level of eggs laid later within the clutch ("b-eggs") was significantly higher than that of eggs laid earlier ("a-eggs"). The yolk testosterone levels of both a- and b-eggs of later breeders were significantly higher than those of earlier ones, while this trend was not observed in mean egg mass. Our results indicate that mothers establishing the clutch later in the season would invest more maternal testosterone into the clutch.

Seabird populations, important components of the marine ecosystem, are decreasing due to human activity impacting the oceans. In order to conserve seabirds, it is essential to conduct monitoring studies of seabirds and to understand how factors affect the dynamics of their populations and their breeding success. Here we introduce methods of seabird monitoring on beaches and oceans, including beached bird surveys and ferry censuses, and explain their fundamental significance for monitoring studies. In beached bird surveys, researchers record the carcasses of seabirds found while walking along a certain length of beach. Citizens interested in seabird conservation can easily conduct such surveys and contribute to continuous monitoring studies. During censuses from ferries, researchers count the seabirds resting on the sea surface or flying from the vessel and record their behavior. Research vessels, trading ships and ferries can all be used for such censuses. Censuses from ferries are feasible for amateur birdwatchers with binoculars. Seabird researchers aim to identify &ldquo;Marine Important Bird Areas (Marine IBA)&rdquo;, areas and habitat seabirds use frequently. Ferry censuses can provide important information to detect Marine IBA. Beached bird surveys conducted by amateur birdwatchers play an important role in providing information on the occurrence of oil spills and bycatch in Marine IBA. Beached bird surveys and ferry censuses conducted by amateur birdwatchers are expected to be extended and carried out at many sites continuously.

Often in colonial seabirds, all colony members are believed to defend against nest predators and experience equal nest predation risk. However, the variation of defense behavior among members and its reproductive consequences are largely unknown. We investigated (1) individual variation in the nest defense of breeding Black-tailed Gulls Larus crassirostris against a natural egg predator, the Jungle Crow Corvus macrorhynchos and (2) how this behavioral variation affects an individual&apos;s own nest predation risk and that of their neighbors. Results were compared between 2 years where crow attack levels were manipulated to average 5 and 22 times normal rates ("low" and "high" predation risk years, respectively) by the placement of varying numbers of artificial nests containing unguarded eggs at the perimeter of the gull colony. In both years, 23-38% of parents, mostly males, showed "aggressive" defense behavior (strikes or chases) against crows and decoys. Other "non-aggressive" gulls showed no defense. In the year of low predation risk, intrusion rates by crows (landing within 0.5 m of an individual gull&apos;s nest) were similar for aggressive and non-aggressive gulls. In the year of high predation risk, however, the rates of intrusion for aggressive gulls (4%) and for non-aggressive gulls with an aggressive neighbor (37%) were significantly lower than for non-aggressive gulls without an aggressive neighbor (76%). These results indicate that aggressive individuals reduce nest predation risk for themselves and conspecific neighbors in a colonially breeding species.

Since parent birds are hypothesized to adjust the level of their nest defense against predators so as to enhance the survival of their offspring, parental nest defense is expected to increase in intensity in relation to increasing clutch size. Empirical studies of bird species, in which clutch sizes have been manipulated artificially, however, have produced results contradicting such expectations, partly, it is thought, because of various errors in experimental design, such as a lack of nesting habitat control, or providing too short a time for parents to assess the value of the manipulated clutch. Hence, further evidence needed to be gathered to clarify whether the basic hypothesis is adequately supported. We manipulated the clutch size of Black-tailed Gulls Larus crassirostris and observed the responses of male parents to a crow decoy in controlled nesting habitats. The intensity of defense was not affected by the clutch size. Opportunities for future reproduction, or constant individual levels of aggressiveness of seem to best explain the observed intensity of nest defense in these long-lived Black-tailed Gulls, rather than the value of the current clutch.

For sustainable use of marine resources, ecosystem based management is essential. However, collecting and integrating all the information needed is difficult. Thus it is important to use effective indicators of marine ecosystem change. Seabirds are believed to be useful biological indicators of marine ecosystem changes and marine pollution. In this paper, we review: 1) the responses of seabird to climate driven marine ecosystem changes, 2) the usefulness of seabirds as indicators of marine pollution and its potential effect on seabirds, 3) the status and conservation of albatrosses, focusing on the reduction of long-line by-catch. We review the seabird monitoring program globally and propose a seabird monitoring and network in Japan.

Although it is considered that adoption of unrelated chicks is not adaptive, several studies of ground-nesting colonial seabirds have reported adoption of unrelated chicks. These studies revealed experimentally that adoption occurs more frequently for chicks younger than around five days old whereas older chicks tend to be rejected. In experiments, individual unrelated chicks were added to host nests while at the same time individual host's chicks were removed so as to maintain the total number of chicks in each nest. However, it is unlikely that the total number of chicks is maintained after unrelated chicks are added under natural condition. In the present study of the Black-tailed Gull Larus crassirostris, we added an unrelated chick to increase the total number chicks in a nest and investigated the occurrence of adoption in relation to chick' age. We found that, even if the total number of chicks increased, adoption occurred more frequently for younger chicks (less than 4&ndash;6 days old) than for older chicks, suggesting that (1) parents do not use the total number of chicks in their nest to recognize and discriminate additional unrelated chicks, and (2) the cost of adoption must not be very high even when it results in an increase in the total number of chicks.

We investigated telomere length of Black-tailed Gull Larus crassirostris (chick and adult) in Rishiri Island, Hokkaido and Kabushima, Aomori in relation to their age. DNAs were extracted from their bloods and detected telomere length. Telomere lengths were significantly decreased with gulls' age. But coefficient value was too small because of large variability of telomere length in both chick and adult. We suggest that it is difficult for Black-tailed Gull to estimate their age by using telomere length.

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&plusmn;S.E.: 0.737&plusmn;0.282 ng/ml) was assumed to decline with elapsed days from the onset of incubation, as shown in other species.

In 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 (&lt; 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 &lt; 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.

It has been common to estimate the number of nests and size of breeding populations of colonial seabirds based on two-dimensional (2D) areas. For seabirds breeding in areas with undulating topography, however, any nest distribution area based on the 2D area will be an underestimate, resulting in an underestimate of nest numbers. We investigated the nest density of Streaked Shearwaters according to the vegetation type on Sangan Island, Iwate, and estimated the total number of nests and breeding population in a three-dimensional (3D) area which reflected altitude, using geographical information system (GIS) and compared data with values obtained from a simple 2D area. The vegetation area obtained by the 3D method was 1.3 times that of the 2D area. Based on the conditions of the geographical feature, vegetation, and geology of Sangan Island, the total number of nests estimated by the 3D method was 1.2 times that of the 2D method. The population size parameters of Streaked Shearwaters breeding on Sangan Island obtained by the 3D method were estimated as 101,000 nests, 41,000 fledglings (=fledging nests), and 109,000 breeders during the hatching period. On another island off the same Sanriku coast, storm petrels have decreased in number, caused by the nesting activities of Streaked Shearwaters. It seems apparent that the large population of shearwaters on Sangan Island is excluding storm-petrels, including the endangered Swinhoe's Storm-petrel, from breeding.