The Check-list of Japanese Birds, 6th ed (OSJ 2000) retained a conservative tendency toward lumping, with regards species classification, and it has become conspicuously inconsistent with the international tendency towards splitting. This inconsistency has increasingly generated difficulties with integration in international activities or databases. In considering revisions for the forthcoming 7th edition, I reviewed the significance of recent advances in DNA barcoding, especially those focused on the distinctive features of birds in Japan and East Asia, and examined the international trends in species concepts and species delimitations. Then, I emphasized the importance of further research on the classification of Japanese avian species. DNA barcoding is a project to identify species based on nucleotide sequences from a short target DNA region (mitochondrial COI region in animals). DNA sequence data, with species name, locality, date, data of voucher specimens, and so on, are registered in the Barcode of Life database. About 40% of bird species worldwide and about 96% of Japanese breeding species have already been registered. Barcoding research in the New World suggest that inter-taxon divergences of 2-2.5% should be recognized as a standard measure of species rank, though some recognizable, closely related species are genetically closer than that limit as a result of recent speciation and/or hybridization. The measure of 2-2.5% divergence has also proven to be applicable to birds on the Korean Peninsula and in Scandinavia. Research in Russia and Mongolia has found that 8.3% of bird species have large intraspecific divergences of over 2%. I analyzed the COI sequences of 230 breeding species in Japan combined with those in other Eastern Palearctic regions, and found that 32 species (14%) include clades with more than 2% divergence within them, while 33 species showed less than 2% divergence from closely related species. As an explanation for the many exceptions among Japanese birds and the extent of peripatric speciation on Japanese islands, it is speculated that Japan experienced few population extinctions during the last ice age as a result of glaciers in the archipelago being poorly developed and essentially only montane. Species classification cannot be based simply on DNA barcode sequences, but barcode surveys are a powerful tool for finding those species in need of further biological investigation. Current species concepts divide broadly into two categories, those founded on integrity (or irreversibility) and those based on diagnosability (or monophyly). The two categories have, until recently, been considered contradictory, but new ideas have been put proposed that attempt to reconcile their differences. The General Metapopulation Lineage Concept and Comprehensive Biological Species Concept have enhanced our essential recognition of species. Nevertheless, when compiling a checklist it is necessary to adopt uniform guidelines when assigning species rank. The British Ornithologists' Union, for example, has proposed realistic guidelines for bird species classification. I want to emphasize the need for comprehensive biological research, including: morphology, ecology, behavioral science and physiology as well as molecular biology and taxonomy, in order to make taxonomic decisions. The Ornithological Society of Japan, which is the responsible organization for Japanese bird classification, should pursue valuable research in this direction to confirm its worth.

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Hybridization and genetic introgression have recently drawn increasing attention in evolutionary studies. Since speciation events are mainly regarded as bifurcating phenomena occurring when an ancient population has divided into two species, hybridization has been treated as exceptional. However, recent molecular approaches, especially multi-locus analyses, have revealed the important role of introgressive hybridization. This review introduces recent avian research related to hybridization and genetic introgression. Such events may be grouped into four categories of occurrence, when: 1) two lineages continue to diverge, 2) two separate lineages fuse to become one, in a process known as “de-speciation” or “species fusion”, 3) a new lineage is formed by hybridization of two parental lineages, called “hybrid speciation”, and 4) two lineages are maintained and genetic introgression occurs between those lineages. The importance of studying hybridization and genetic introgression so as to be able to address conservation issues such as genetic contamination by invasive species, is also discussed.

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Contributing factors for accelerating or decelerating speciation rates in birds were reviewed and discussed. Recent empirical studies do not support the hypothesis that differences in species richness among bird lineages are simply due to chance. High species diversity in some avian families and parvorders has been shown to be significantly associated with intrinsic biological factors including: large brain size, behavioral flexibility, feeding generalism, strong sexual selection and high mutation rates. Many ornithologists have considered gene flow to be a factor that strongly inhibits speciation, but some recent theoretical and empirical studies suggest that speciation-with-gene-flow might be an easier event than previously thought and that it has occurred in birds.

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The Short-tailed Albatross Phoebastria albatrus is a vulnerable seabird species that breeds in two island groups in the western part of the North Pacific Ocean. In the 2006/07 breeding season, the world population was estimated at around 2,360 individuals: 80% of them breeding on Torishima, and 20% on two islets of the Senkaku Islands. The species is tacitly regarded as a single management unit and international conservation efforts consider its population structure to be of low concern. However, our previous study showed that two populations of the Short-tailed Albatross existed about 1,000 years ago. During the late 19th and early 20th centuries the species was exterminated at most breeding colonies, with descendents of each population surviving only on Torishima and the Senkaku Islands. Recently, descendents of the two populations are breeding sympatrically on Torishima. However, it is not known whether they mix or not. Because the mitochondrial DNA haplotype frequencies clearly differ between the Torishima and Senkaku Island birds, each population meets different Management Unit (MU) criteria. These two MUs should be managed as different entities, since the emigration rate from the Senkaku Islands to Torishima may have been reinforced by extensive fowling in the late 19th and early 20th centuries. The sequence divergence between the two clades of the Short-tailed Albatross is greater than that recognized between other sister species of albatrosses. Furthermore, ecological and morphological differences between the Torishima and Senkaku Island albatrosses are indicated. A taxonomic re-examination of the Torishima and Senkaku Island albatross taxa is required through comparative studies of ecological and ethological traits.

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There have been very few studies of the effects of global climate change on migration and breeding of land birds in Asia (including Japan), compared with those in Europe and North America. In this study, we compared banding records of Barn Swallow Hirundo rustica collected in Japan in 1961-1971 (the 1960s) with those in 2000-2010 (the 2000s) to consider climatic effects on their migration and breeding. From the frequency distributions of the numbers of adults, juveniles, and nestling birds released per day, the timing of rapid increase in adults was about half a month earlier in 2000s than 1960s, but the period of rapid decrease of adults did not vary between these two periods. The distribution of juveniles 40 years ago was almost the same as at present. The timing of rapid increase in nestlings was about half a month earlier in the 2000s than in the 1960s. The ratio of juveniles to adults was slightly smaller in the 2000s than in the 1960s. These results indicate that both arrival and commencement of breeding in Barn Swallows were earlier in the 2000s than in the 1960s, but their departure did not vary between the two periods. Furthermore, their annual fecundity was higher in the 1960s than in the 2000s. Changes in arrival date and commencement of breeding, were expected based on other available information, although it was anticipated that there would be effects of different habitats and study seasons between the two periods. Banding records were considered to be invaluable in assessing departure date and annual fecundity, because of a lack of other information suitable for the analysis of long-term change.

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The influence of winter foraging pressure by Bewick's Swans Cygnus columbianus on rhizomes, on the aboveground biomass the following summer, of Zizania latifolia, was investigated at Sugao Marsh, Ibaraki Prefecture, central Japan, from 1998 to 2004. An experimental area was covered with netting to prevent Bewick's Swans from grubbing up Z. latifolia rhizomes during winter. The dry weight of aboveground stalks was measured from quadrats inside and outside the experimental area the following autumn. From the second year, after preventing swans from foraging, the aboveground biomass of Z. latifolia in the experimental area declined, and was lower than the above­ground biomass of Z. latifolia outside the experimental area. Thus, the foraging pressure of swans on Z. latifolia rhizomes in winter positively impacts Z. latifolia growth aboveground during the subsequent growing season.

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Twenty-six Japanese Night Heron Gorsachius goisagi nests were examined during the 2009-2010 breeding season in the West Mikawa area of Aichi Prefecture. All of the nests were found in live broad-leaved trees with an average height of 16.5 m and an average nest height of 10.6 m. Since the forest surrounding the nests was mostly composed of mixed broad-leaved and coniferous species, G. goisagi seems likely to choose selectively broad-leaved trees in which to nest. Moreover, more than 40% of the nesting trees were Prunus spp. Although the population density of Prunus spp. was not high in the study area, the spreading branches of Prunus spp. may provide favorable conditions for nesting. All of the nests were found either at the bottom of, or on the lower slopes of, valleys; none were found along ridgelines. It is suggested, therefore, that well-grown broadleaf trees situated within valleys are preferred for nesting.

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