The origin of birds has been a fundamental and challenging subject in ornithology since the discovery of Archaeopteryx. Although the phylogenetic relationship between birds and crocodiles has been recognized since the beginning of discussion, researchers were unable to reached a consensus as to which was the ancestor of modern birds. Pterosauria, Crocodilia, Thecodont, Ornithischia, and Theropoda have all been put forward as the ancestors of birds. Recent paleontological studies have clarified that birds are derived from a clade of Maniraptora in the clade Coelurosauria among the Theropod dinosaurs. Fossil evidence has demonstrated that birds share several features with Coelurosauria dinosaurs, such as bipedal locomotion, fork-shaped furcula, air sacs, and laterally flexing wrists. Embryological and molecular biological evidence correspond with this view. Today, birds are phylogenetically defined as avian dinosaurs, and other dinosaurs are defined as non-avian dinosaurs. This implies that dinosaurs did not become extinct at the end of the Cretaceous period, 66 million years ago. Feathered dinosaurs represent one of the most remarkable topics of recent paleontology. Various dinosaurs with contour feathers have been found among the Coelurosauria, while simple filament-like protofeathers have been detected in an even wider range of taxa, including the Ornithischia. Furthermore, flightless Ornithomimus edmontonicus has been shown to have possessed pennaceous wings. These findings imply that non-avian dinosaurs evolved feathers and wings for reasons unrelated to flight, perhaps for display. While toothless beaks, the pygostyle, shortened tails, and keeled sternums are considered to have evolved for flight, bipedalism, air sacs, and furcula are considered to be cases of exaptation. The fields of ornithology and paleontology may contribute to each other based on the close relationships between birds and dinosaurs. Collaboration between these two fields is essential for their future development.

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Archosaurs (e.g., crocodilians, pterosaurs, and dinosaurs including birds) are the most diverse and successful clade of terrestrial vertebrates. An understanding of the nesting methods and behaviors of both extinct (e.g., non-avian dinosaurs) and extant archosaurs (i.e., crocodilians and birds) is crucial for the advancement of our understanding of the evolution and diversification of this clade. The nesting methods and behavior of extinct taxa cannot be directly observed from the fossil record, thus aspects of nesting (i.e., nest type, incubation behavior, and incubation period) may only be inferred and reconstructed based on certain features of fossil eggs, nests, and embryos (e.g., clutch size, egg mass, eggshell porosity, and embryonic osteology). Nests and nesting behaviors were likely to have been diverse among non-avian dinosaurs, and the evolution of these features in archosaurs is discussed.

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Since the 1990s, the avian fossil record has been greatly advanced with the oldest record found from the Upper Jurassic and a pan-global distribution discovered in the Cretaceous. Birds possess highly modified skeletal characteristics such as the pygostyle, keeled sternum, forelimbs developed as wings, and toothless jaws, all of which are considered to have evolved in relation to flight. Recent discoveries have also revealed that Mesozoic birds had made various ecological developments including sexual dimorphism and differential growth rates. Although the reasons for the limited diversification of flightless birds in the Mesozoic and for the survival of the Neornithes through the K-Pg mass extinction event are still not well understood, they may be attributed to environmental and physiological limitations. In this paper, I suggest that the development of flight capability, endothermy, and efficient digestive systems may have been involved in the diversification and wide geographical distribution of birds. Although physiological characteristics are rarely preserved in the fossil record, new fossil discoveries and advancements in research on soft tissue reconstruction might reveal more details of the ecology of extinct birds in the near future.

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Hesperornithiformes were toothed, foot-propelled diving birds and among the most widely distributed groups of birds in the Cretaceous (Late Albian to Maastrichtian) in the Northern Hemisphere. The first species of this group, Hesperornis regalis was discovered from the Niobrara Formation (Upper Santonian) in Kansas in 1871. H. regalis had extremely reduced forelimbs, powerful hind limbs, and a non-keeled sternum. Taking into consideration the osteological features mentions above, this huge diving bird was obviously a flightless foot-propelled diver. Currently, Cretaceous Hesperornithiformes are recognized as the oldest diving birds in the avian evolutionary history. Thirty-one species and at least fifteen genera have been named so far. Most of the known hesperornithiform remains have been recovered from the marine deposits of the Western Interior Seaway in North America, especially from Kansas and South Dakota in USA and Manitoba and Saskatchewan in Canada. In Europe, some hesperornithiform remains have been found from the Cretaceous deposits of the Turgai Strait (Russia and Kazakhstan), but Hesperornithiformes are extremely rare in Asia where they are only known from three remains from Mongolia and Japan. Current phylogenetic analyses of Mesozoic birds suggest that these diving birds are one of the closest relatives of the Neornithes (modern birds). In this article, we review the current knowledge of the origin of the Neornithes, the phylogeny of Mesozoic birds, and hesperornithiform osteology and paleoecology. We also discuss future prospects for research into these oldest diving birds.

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Life history studies of the Japanese Rock Ptarmigan Lagopus muta japonica provide important information on this subspecies' adaptation to cold environments and the effects of global warming on it. In this study, we examined the breeding and wintering ecology, seasonal flock composition, and altitudinal movements of the Japanese Rock Ptarmigan on Mt Norikura. In relation to seasonal changes in the weather conditions of the alpine zone, the size and composition of ptarmigan flocks varied five times within a year reflecting stages of the life cycle: movement to the breeding area, commencement of incubation, the hatching period, the beginning of independence from parental care, and movement to the wintering. All birds left the alpine zone in winter, but gender segregation of wintering areas occurred. Males observed in a wintering area had bred in areas nearby. However, the area in which females wintered (as revealed by radio tracking), was steeper and at lower elevations than males. Realized sex ratios were skewed towards males throughout the year, but observed sex ratios varied in relation to changes in ptarmigan life history. Taken together, our findings revealed that in comparison with foreign populations and related species the Japanese Rock Ptarmigan exhibits complete separation of breeding and wintering areas but lacks summer movements to higher elevations as reported in other subspecies or related species of other countries. We suggest that these characteristics of the Japanese Rock Ptarmigan may be in response to heavy snow in winter and to the distribution of alpine vegetation in the alpine zone. Finally, we suggest that among alpine ptarmigans the subspecies of the Rock Ptarmigan in Japan is the most sensitive to global warming.

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The natural habitat of the Large-billed Crow Corvus macrorhynchos in Japan is considered to be forest. We investigated the occurrence of this species in montane areas of Japan to elucidate its habitat selection. In montane areas, crow numbers tended to be lower than in urban area such as in Tokyo. Crows were likely to occur in higher numbers in areas where human activity was greater; however, occurrence was not correlated with altitude. Notably, crow density was higher in evergreen broad leaved and coniferous forests than in deciduous forests. Nesting in evergreen forests is suspected to be adaptive because the crows may avoid nest predation there because of the reduced visibility.

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Black-tailed Gull territorial defense was compared between plots with tall (2-3 m high) and sparse vegetation. While the frequency of defense against neighboring breeders did not differ between these plots, defense against intruders was 8 times greater in plots with sparse vegetation than in those with tall vegetation. When we removed vegetation from a plot with tall vegetation we found that gulls sometimes landed in this newly opened area, whereas landings did not occur in areas with tall vegetation. Such behavior indicates that tall vegetation prohibits intruders from landing and thus reduces the frequency of territorial defense.

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A call playback survey of wintering Swinhoe's Rail Coturnicops exquisitus was conducted at 65 wet grasslands within the Kanto Region from late December to mid-February in three winters (2014-2017). We located 98 individuals at 18 survey sites where were divided into seven regional groups. Many sites included farmland with abandoned rice fields or riverbeds. The presence of farmland had a positive effect on the number of rails located. In this study, Swinhoe's Rails were observed in medium-height reed beds with reeds of less than approximately 2.0 m and with abundant understory, suggesting that the vegetation structure is important for wintering Swinhoe's Rails.

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From 1991 to 2001, seasonal change in the daily song activity of the Meadow Buntings was observed throughout the daytime on a total of 158 days, in Kanazawa City, Ishikawa Prefecture. After the period of being single in the spring, the song frequency of all individuals decreased during the pairing period and decreased again after the incubation period during the nestling period. Moreover, the song frequency of all birds increased during the period when they were single after the nestling period and during the nest building period after the pairing period. Compared with the period immediately before the molt, song frequency decreased by ≥ 90% in all four individuals during the molting period during early and mid August. The number of song bouts differed greatly throughout the year and even among days of the same breeding stage. The results suggest that the presence and behavior of females and the roles of males during each breeding stage may affect song frequency in this species.

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