Nest form and nesting habitat are important for a bird's breeding success due to their influence on the risk of breeding failure. The Japanese Marsh Warbler Locustella pryeri, which breeds in wet grasslands under habitat management, builds three types of nests: deep-cup Type I, domed Type II without decoration, and domed Type III decorated with live grasses. Relationships among nest types, habitat management, and nesting microhabitat characteristics were examined in the Hotokenuma wetland in northern Japan. During the breeding seasons in 2007–2010, a total of 263 nesting attempts were monitored, and 16 Type I, 61 Type II, and 25 Type III nests were measured. Prescribed burning affected the determination of nest type, and warblers built Type III nests frequently after burning. The microhabitat around the nests differed among the three nest types. Type II nests were constructed in wet conditions with abundant dead understory vegetation. In contrast, Type III nests were built in dry conditions with abundant live understory vegetation. Type I nests showed characteristics intermediate between those of the two domed types and were also found in spots with abundant hard stems. Nest type, habitat management, and nesting microhabitat did not affect nest predation or breeding success. We conclude that nest type differs depending on the characteristics of the nesting habitat.
We analyzed existing records of the presence and breeding of three water bird species (Little Grebe Tachybaptus ruficollis; Common Moorhen Gallinula chloropus; and Spot-billed Duck Anas zonorhyncha) at 1,087 ponds in Osaka Prefecture to estimate the effects on them of various environmental, geographical, and social factors. A conditional autoregressive (CAR) model, incorporating spatial structure as a random effect, was applied in the analyses. Results show a significant positive effect of a broad shape of the water surface, which indicates the importance of threats by terrestrial enemies, on the probability of the presence of each species. Two human social factors affected the probability of breeding of two bird species: human population density negatively affected the breeding probability of T. ruficollis and A. zonorhyncha; and the retail store density, an index of development as a commercial area, positively affected the latter species. Spatial random effects reflecting unmeasured factors were large and comparable to other measured factors. Different patterns were exhibited among the three species, demonstrating that other important factors were overlooked and that these effects should be assessed by application of methods such as the CAR model.
Small woodpeckers have weak excavation capabilities presumed to be affected by tree characteristics. To determine the features of trees preferred by the Japanese Pygmy Woodpecker Dendrocopos kizuki, we compared 50 excavated trees (8 for nesting, 10 for roosting, and 32 old cavities) with 280 unused trees in a natural mixed forest in Hokkaido, Japan. The woodpeckers tended to excavate cavities in larger trees, and preferred decaying trees over living trees. Dominant tree species, such as birches Betula platyphylla and oaks Quercus crispula, tended to be avoided in favour of particular trees especially alders Alnus hirsuta. These results suggest that small woodpeckers select particular trees, with softer wood, in which to nest and roost on the basis of their weaker excavation ability.
Greater White-fronted Goose Anser albifrons has a holarctic breeding distribution and is polymorphic. Three subspecies winter in the Palaearctic region, one of which also winters in the Nearctic region: European White-fronted Goose A. a. albifrons breeds in the far north of Europe and Asia and winters in the south and west of Europe; Pacific White-fronted Goose A. a. frontalis breeds in east Siberia and Arctic Canada and winters in East Asia and United States; and Greenland White-fronted Goose A. a. flavirostris breeds in Greenland and winters in Ireland and western Scotland. The phylogenetic relationships among these three subspecies are unclear. We determined the mitochondrial DNA control region sequences of Pacific White-fronted Goose, using 66 shed feathers collected from wintering sites in Japan, and compared the sequences with those previously published for Greater White-fronted Goose subspecies. Phylogenetic trees and networks revealed that there are three clades within the species. The sequence divergence among the clades corresponds to divergence long before the last glacial maximum (15–25 thousand years ago), which suggests the existence of at least three ancient refugia for the species. However, all three subspecies consist of haplotypes from two of the three clades. This suggests that they originated from individuals that survived in two refugia during the last glacial period.
To assess the impact of urban sprawl on avian biodiversity, many studies worldwide have tackled the question of which birds are able to inhabit urban areas. Some studies have suggested that ecological characteristics of birds are important. Other studies, however, have suggested that interspecific competition can regulate urban avian communities. In order to examine whether interspecific competition is primarily responsible for community structure, we investigated the degree of co-occurrence of ecologically similar species in the urban avian community in the Kanto region of Japan. They should not coexist if interspecific competition is strong. On comparing the observed avian community with virtual communities, we did not obtain any evidence of interspecific competition regulating the urban community. The main mechanism behind formation of an urban avian community structure appears to be the ecological traits of the species.
The Bonin White-eye Apalopteron familiare is a threatened endemic species of the Bonin Islands. This white-eye exists on one inhabited island, Hahajima, and its two small satellite islands. Although species used to occur in both the Mukojima and Chichijima island groups, the subspecies there is now extinct. Local extinctions have been attributed to a combination of habitat loss resulting from cultivation and predation by feral cats and introduced rats. The same factors may also be threats to the existing population of white-eyes on Hahajima. Therefore, we estimated the current population size of the white-eye and, using a model simulation we assessed the impacts of: habitat loss, which affects carrying capacity; and predation pressure, which affects breeding success. Population size was estimated taking into consideration variations in population densities among habitat types. The population was estimated to be about 14,700 on Hahajima, and 480 and 420 each on the two satellite islands. A population viability analysis using empirical parameters obtained during field surveys showed almost no extinction risks for any of the three populations under present circumstances. The potential for extinction would drastically increase if the carrying capacity fell to less than 40% of its present status on the small satellite islands. The current findings also indicated that the extinction probability would rise sharply if breeding success dropped to 70% (10 points lower than the current breeding success), on the small islands. The frequency of predation and the population dynamics of the white-eyes must be monitored in order to detect any changes to the species' extinction risk on the islands.
We collected fresh Streaked Shearwater Calonectris leucomelas carcasses and describe sex differences in external measurements following sex identification using reproductive organs. Males had significantly deeper bills, longer bills, longer heads, longer tarsi, greater wingspans and greater wing areas than females, but overall wing and tail lengths and aspect ratios did not differ between sexes. Streaked Shearwaters showed a greater degree of sexual dimorphism in bill size than other Puffinus species. Comparing the wing loadings of male and female Streaked Shearwaters, the mass increase required for females to have the same wing loading as males is 0.036 kg. Females could feed to increase their body mass during a foraging trip to have similar wing loading to males.
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