Linkages between terrestrial and aquatic ecosystems offer important routes through which energy and marine-derived nutrients flow. These linkages serve to maintain ecosystem structure and function, and are essential aspects of the maintenance of the health of terrestrial ecosystems. The carcasses of anadromous salmonids are dispersed to terrestrial areas after spawning, and the nutrients in these carcasses are particularly important in the Northern Hemisphere. Terrestrial vertebrates, such as mammals and birds, mediate much of the nutrient transport through salmon carcasses and are therefore essential for maintaining the link between terrestrial and aquatic areas at the watershed scale. Urbanization has a strong impact on riparian communities, which interact with both terrestrial and aquatic ecosystems. However, few studies have been conducted on the effects of urbanization on these linkages with terrestrial vertebrate consumers that disperse energy over large areas. We investigated the effects of urbanization on scavenging avian communities and their total salmon carcass consumption in a salmon spawning river. We selected 17 study sites along 12 salmon spawning rivers in western Hokkaido, northern Japan. We recorded the number of scavenging birds of each species, and calculated the total salmon consumption by birds. We also calculated salmon carcass biomass, proportion of the urban area, channel width, and the distance from the coast. Based on these factors, we clarified the relationships between the abundance and species richness of scavenging birds, carcass consumption, and factors, using piecewise structural equation models. We found that both scavenging bird abundance and their total salmon consumption had unimodal responses to urbanization intensity. Our results suggest that urbanization has wide-scale effects on the strength of the linkages between ecosystems, including at the watershed scale. Suburban or peri-urban areas may also be important for maintaining local ecosystem functions.
Geographic variation in the clutch size of Varied Tit Sittiparus varius, a common nest-box breeder in East Asia, was reviewed and analyzed using a parametric bootstrap approach to investigate the relationship between clutch size and latitude, subspecific classification, and habitat size. We collected 49 data sets from study sites ranging from 26 degrees 46 '' N to 42 degrees 40 '' N and found an evident geographic variation in the local mean clutch size ranging from 3.7 to 7.6 eggs. Parametric bootstrap analyses showed a latitudinal increase in clutch size, with an average of 0.184 eggs per degree. Population isolation as a subspecies was identified as another influential factor in clutch size variation for one of the four subspecies examined, i.e., S. v. owstoni, which inhabits small islands far south of the Japanese main islands. However, the effect of habitat size (islands smaller than 100 km2) was not significant, although the clutch size on some small islands tended to be smaller than that of nearby larger habitats. Such a variation in clutch size of the Varied Tit indicates there is a conspicuous geographic variation in its life history. The clear latitudinal gradient of clutch size observed in the Varied Tit may help us to understand environmental influences better, as the factors that change independent of latitude may have a lower contribution to such a clutch size variation.
Japanese Weasel Mustela itatsi has been introduced to various regions of Japan in an attempt to control rodents, raising concerns about its negative impact on native fauna. However, there is little direct evidence of predation on birds in the Ryukyu Islands. Here, I report weasel predation on Ruddy Kingfisher Halcyon coromanda and Ryukyu Scops Owl Otus elegans on both Hateruma and Minami-Daito islands. This is the first photographic and videographer evidence of weasel predation on birds in this region, with clear species identification of prey, contributing to the advancement of weasel control on a scientific basis.
Caprimulgidae is an avian family with nocturnal habits and a wide global distribution; 15% of the species in this family face conservation concerns. Grey Nightjar Caprimulgus jotaka has declined dramatically in Japan in recent decades. We investigated the distribution of nightjar territories and nest sites in semi-natural grasslands at the foot of Mt. Fuji, an active volcano. Although these grasslands support high biodiversity including rare species, there is no ecological information on nightjars living in the grassland habitats. Territories were mainly located in and around the lava flow in vast grasslands with sparse woodland, and nests were found only along ridges created by lava flows and not in areas of volcanic fan deposit. Nest sites had larger gravel, more bare ground, and lower mid-height (1-1.5 m) vegetation cover than non-nesting sites. These results suggest that burned, volcanic, semi-natural grasslands provide suitable habitat for nightjars for both the establishment of territories and for nest sites. Semi-natural grasslands are often located on active volcanoes throughout Japan and are artificially maintained through various management practices. Thus, future research should investigate the effects of grassland management and geographical features on the distribution of nightjars in these semi-natural grasslands, to support their conservation.
The rapid global expansion of wind farms poses potential impacts to bird populations through collision mortality, movement barriers, and habitat displacement. Avoidance, the tendency of birds to maintain distance from wind turbines, plays a critical role in assessing the impacts of wind farms on avian species. In this study, we used marine surveillance radar to monitor avian responses to the Formosa 1 Offshore Wind Farm in the eastern Taiwan Strait. We assessed macro-avoidance by analyzing flight track directions and comparing bird density within and outside the wind farm area. Our findings suggested macro-avoidance rates ranging from 0.33 to 0.69 between March and May, and from 0.83 to 0.89 between July and January. The lower avoidance rates observed in spring could be partially attributed to the high proportion of egrets during this period, as these birds generally exhibited little macro-avoidance behavior in terrestrial observations. Discrepancies between the two methods used to assess avoidance were identified, with radar signal interference from wind turbines likely leading to an overestimation of avoidance rates in the track-density method. Low avoidance between March and May suggested a potentially higher collision risk during spring migration. Further investigation into finer-scale avoidance behaviors and collision rates is essential to understand the ecological impact of wind energy development.
Yellow-breasted Bunting Emberiza aureola was a once an abundant summer migrant in the Northern Palearctic, but its population collapsed during the 1990s. The aim of this study was to clarify the breeding distribution of Yellow-breasted Bunting before and during the population collapse periods in Hokkaido, and then, I examined the habitat characteristics including vegetation and elevation. Distributional data were collected through a questionnaire survey of birdwatchers and from published data. In total, 5,264 observation records were collected. These data were summarised into 240 distribution points on a 10-km square scale. The distribution points were widely spread in coastal areas and in the middle and lower reaches of rivers and were abundant in the Eastern and Northern areas but fewer in the Western and Southwestern areas of Hokkaido. Yellow-breasted Bunting was mainly distributed in wetland vegetation, which might be its most important habitat. Natural grassland or anthropogenic habitats such as pastureland or crops, including rice and weedy fields, were also of major importance. From the elevation survey, Yellow-breasted Bunting occurred mainly in the range of 0-99 m above sea level, with its main habitat defined as lowland. Although the current population status of Yellow-breasted Bunting is still severe, the distribution map and habitat investigation revealed by this study will provide some important evidence for considering future conservation measures.
Urban birds exhibit flexible behavior towards humans, such as deciding to fly or stay, depending on their distance from an approaching human. To date, no studies have examined the physiological activity of urban birds in response to an approaching human. Here, we report the autonomic responses of captive Large-billed Crow Corvus macrorhynchos to approaching humans in an experimental setting. Electrocardiograms of the crows, recorded while the experimenter approached the bird, were analyzed to determine the autonomic activity. We found a drastic reduction in heart rate and sympathetic nervous activity when the human reached a distance of <= 10 m.
Understanding the behavior and movements of fledglings after leaving the nest is crucial for assessing their survival rate and the long-term viability of populations. In this study, we tracked Black-tailed Gull fledglings from Kabushima Island (Kabushima), Japan, using biologging devices that recorded GPS locations and overall dynamic body acceleration. All fledglings that survived for up to nine months after leaving the island traveled over 800 km and did not return to the island before at least the following breeding season. Additionally, they were predominantly active during the daytime, in contrast to breeding adults, which have been reported to be active during both day and night. These differences may reflect the juveniles' limited flight or foraging capabilities, or the ecological demands on breeding adults.
Nest sites of both Chestnut-cheeked Starling Agropsar philippensis and White-cheeked Starling Spodiopsar cineraceus were compared in Morioka City, a core city in the Tohoku region of Japan. Surveys were conducted in June 2023 and from April to June 2024; these involved walking along all roads within 500 m square grids to locate nests of both species. Nests were classified based on their location, and the following variables were measured: nest height, structure height, entrance orientation, and entrance angle. Totals of 51 Chestnut-cheeked Starling and 47 Whitecheeked Starling nests were observed across 32 survey sessions. When comparing nest location categories based on land use, significant differences were observed in the nest site selection of Chestnut-cheeked Starling breeding in urban areas compared with those in agricultural areas and with White-cheeked Starling breeding in urban areas. The nests of Chestnut-cheeked Starling breeding in agricultural areas were significantly lower than of those breeding in urban areas or of White-cheeked Starling breeding in agricultural areas. Whereas some of the Chestnut-cheeked Starling nests had upward-facing entrances, those of the White-cheeked Starling had more downward-facing entrances. These findings suggest that, to avoid competition with White-cheeked Starling, Chestnut-cheeked Starling may alter its nesting locations in urban areas and and nesting heights in agricultural areas, and this might be disadvantageous for its breeding strategy.
Climate change restructures biological communities, particularly during winter. We investigated bird assemblages in the subalpine zone (2,100-2,520 m a.s.l.) on the eastern slopes of Mt. Norikura, central Japan, during the coldest period of the year, from January to February, over four winters from 2019 to 2024. Nine bird species were recorded over four winters. Of these, seven species were recorded in one or two years. Willow Tit Poecile montanus and Japanese Pygmy Woodpecker Dendrocopos kizuki were recorded in all four winters. The present study provides an early 21st century baseline for future comparisons.
The population of Common Murre Uria aalge on Teuri Island, northern Hokkaido, Japan declined until nearly extirpated (15 birds with no fledglings) in 2005, despite restoration actions being conducted based on social attraction in a safer nesting site in a cave. Large-billed Crow Corvus macrorhynchos and Slaty-backed Gull Larus schistisagus, predated both eggs and chicks. Since 2011 culling of these avian predators has been conducted and the breeding activities of murres nesting in the cave were monitored with direct observation in 2011 and with video cameras in 2012-2016. The maximum number of birds in the cave increased at an annual rate of 24.4% from 2007 to 2016, raising the population to 38 birds in 2016. The number of fledglings per egg-laid (74%) was higher than that before 2010 (33%). Pairs laying earlier and occupying rock wall, which seemed to be more secure against avian predators, produced more fledglings per egg-laid. Culling of avian predators seemed to allow the increase in productivity. Population viability analysis with this increased productivity indicates that immigration from other colonies is likely, and predicts that in 50 years the population may reach 2,099 birds in the case of sustained adequate conditions of the quality and quantity of habitat including nest sites.
We present cases of Brown-throated Martin Riparia paludicola roosting and nesting in disused burrows of European Bee-eaters Merops apiaster, and participating in the latter's nest defense. In one case, Brown-throated Martin nested in the same burrow between two successive nesting episodes of European Bee-eater. Brown-throated Martin collectively mobbed a snake that was predating the European Bee-eater's chicks inside the "shared" burrow, suggesting possible benefits for beeeaters whose burrows are also used by Brown-throated Martin. The martins benefit by gaining nesting and sheltering sites in winter. However, negative implications of this mutualistic relationship, such as competition and parasite transmission, are still to be investigated.
In Japan, Crested Ibis Nipponia nippon is a special natural treasure and a specified national endangered species of Wild Fauna and Flora. This species became extinct in the wild in Japan in 1981. The current captive population, which was established in Japan in 1999, stems from a total of seven founders provided by China to facilitate captive breeding for release back into the wild. Since the reintroduction program was initiated in 2008, the captive population has played a critical role as the source of the released birds and hence the gene pool of the reintroduced population. In this study, several population genetic parameters and the genetic diversity of the captive population were estimated using pedigree data of individuals including all of the founders. The effective population size was estimated to be 11.2 in 2004 and 25.8 in 2021 with a gradual increase in recent years. The average degree of inbreeding was 2.2% in 2004 and 8.9% in 2018, after which it began to decline. The effective number of founders was 2.67 in 2004, rising to 4.96 in 2021, while that of non-founders was 22.8 in 2021. The value of founder genome equivalents was 4.08 in 2021, showing a consistent increase from 2.38 in 2004. The total loss of genetic diversity in 2021 was 0.123, and had decreased steadily from 0.210 in 2004. This was found to be attributed to the losses of 0.071 (58%), 0.029 (24%) and 0.020 (18%) due to the limited number of founders, the unequal genetic contributions of founders, and the population bottleneck and Mendelian sampling, respectively. In conclusion, while this study has revealed generally desirable trends of genetic diversity and population genetic parameters over about 20 years, it is suggested that further efforts should be made to increase genetic diversity beyond the current level.
Climate-driven changes in the abundance, distribution, and migration patterns of forage fish affect the diet composition of seabirds. Decadal climate changes, known as regime shifts, have occurred several times in the Sea of Japan, influencing the food web and leading to shifts in the diet of diving seabird species. To examine whether a long-range surface-feeding species, Streaked Shearwater Calonectris leucomelas, switched diet in response to the 2013/2014 regime shift, we sampled 826 stomach contents from individuals at Awashima Island between 2008 and 2020. They fed mainly on Japanese Anchovy Engraulis japonicus and Bullet Mackerel Auxis rochei, with benthic fish as minor prey, both during the negative and positive phases of the Pacific Decadal Oscillation (PDO) before and after the 2013/2014 regime shift, thus showing no evidence of prey switching. Although fisheries landings of Japanese Anchovy and Bullet Mackerel showed decreasing trends after the 2013/2014 regime shift, with a rise in cold-water Japanese Sardine (Sardinops melanostictus) dominance, this change was not reflected in the shearwater diet. Streaked Shearwater, a highly mobile and adaptable seabird species with an extensive foraging range, maintained a relatively stable diet, even under unpredictable environmental conditions including climate shifts.
Mercury (Hg) contamination impacts the corticosterone stress response via the hypothalamic-pituitary-adrenal axis in some bird species. Any alteration of the normal function of the stress response can have adverse effects on physiological functions, health and survival. However, the effects of Hg on the stress response vary between bird species. In this study we investigated the relationship between Hg concentrations and corticosterone levels in the blood of Black-tailed Gull Larus crassirostris to understand the effect of Hg contamination on the species' corticosterone stress response. We found no effect of Hg on corticosterone levels in adult Black-tailed Gull. One possible reason for this may be related to the lack of correlation between Hg accumulation in the blood and Hg accumulation in the adrenal glands, the main organ that regulates corticosterone levels.
