The Class Aves is a traditional subject for studies of life-history evolution, yet the evolutionary mechanisms contributing to their diverse life-histories are still under discussion. Ricklefs (2000a) divided the history of research into life-history evolution into two periods; during the first period natural selection was established as the primary formative mechanism of life-history evolution, and during the second period (continuing until the present day) the idea that the evolutionary response to selection provided the basis for understanding variation in life-history traits among organisms was examined. In about 2000, several new perspectives were provided on life-history evolution: i.e. the evolution of life-history traits other than clutch size (e.g. developmental rate), the exploration of new selection pressures affecting life-history, and understanding the intrinsic mechanisms of the evolution of life-history. Thus more recent studies are useful in creating a foundation for the comprehensive explanation of evolutionary mechanisms of varied life-histories. In this review, I have listed and organized almost all of the environmental factors that are believed to have an evolutionary effect on avian life-history traits. Studies are separable into two types, those that detect the effects of environmental factor on individual or intra-population life-histories, and those that evaluate evolutionary change of life-history traits by means of inter-specific or inter-population comparisons. The latter approach is relatively scarce. Finally, I discuss future issues for studying avian life-history evolution and the effectiveness of studying these issues in Japan.

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The latitudinal gradient in clutch size, with birds in tropical areas having smaller clutches than those in temperate areas, was first described by ornithologists in the 1940s. Although many hypotheses to explain this gradient have been proposed they are based on life-history evolution in the temperate region where fewer than 25% of bird species occur. The latitudinal gradient in clutch size may be explained not only by geographical variation in food abundance and nest predation risk, but also by several other constraints, such as ambient temperature directly affecting egg viability, physiological tradeoffs (i.e., immune, metabolic, endocrine systems), and physiological regulatory networks that avoid hyperactivation and ensure autoimmune responses. To develop a more comprehensive understanding of the evolutionary mechanisms of plasticity of clutch size within individuals, and variation in clutch size among populations and species, I review works that: (1) clarify the effects of seasonal change and latitudinal gradient in ambient temperature on egg viability, (2) deal with relationships among life histories, selective factors, and physiological costs (e.g, immunological defense against parasites). Thus, I highlight the importance of understanding the effects of local environmental and physiological factors on clutch size variation.

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Birds show enormous variation in their social organization. Many empirical studies of variation in social behavior within-populations or between related species have revealed associations between ecological factors and such variation. Recently, a new notion that life history factors have played an important role in the evolution of social organization in birds has been put forward. The phylogenetic comparative method has been widely applied as a powerful tool for solving the relationships between variation in social behaviour, and ecological, life history and environmental factors. Here, I review studies that have investigated the link between life history traits and variation in avian social organization, particularly mating systems, extra-pair paternity, intraspecific brood parasitism, cooperative breeding systems, and family formation. A hierarchical view is useful for understanding the evolution of social organization and suggests that interspecific variation of social organization is due to a combination of life history predisposition and ecological facilitation.

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In many bird species, males commonly feed their mates during the breeding season. Feeding by males to females has been studied from the behavioral ecological perspective such as sexual role, sexual conflict, and the maintenance of the pair bonding. Previous studies have identified various functions of feeding by males to females that are related to individual fitness. These studies have helped us to understand the relationship between males and females in their breeding. In this review, I examine hypotheses explaining the function of feeding by males to females during the breeding period: before pair formation, from pair formation to egg-laying, and during the incubation period. I also discuss the evolution of this behavior. I introduce the following hypotheses in this review: (1) female choice before pair formation, (2a) female nutrition, (2b) copulation in exchange for food, (2c) mate appraisal, and (2d) pair bond from pair formation to egg laying, and (3a) female nutrition, (3b) mate appraisal, and (3c) pair bond, during the incubation period.

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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 (δ¹⁵N, 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 δ¹⁵N and δ¹³C (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 δ¹⁵N of blood cells that reflected TL during the pre-laying period did not affect the egg volume index. δ¹⁵N of breast feathers that reflected TL during the molting period also did not relate to egg volume index. δ¹⁵N and δ¹³C of feathers and blood of females did not correlate with those of egg yolk, albumen, or egg membrane.

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Morphological and histological studies to analyse the characteristics of the glandular stomach and the gizzard of Large-billed Crows Corvus macrorhynchos and Carrion Crows C. corone were performed using light and electron microscopes, revealing several interspecific differences. The total area of the glandular stomach of C. macrorhynchos was larger than that of C. corone. Although there was no significant difference in the thickness of the glandular stomach wall between the two species, the glandular stomach gland layer in C. macrorhynchos was thicker than that of C. corone, whereas the muscle layer in C. corone was thicker than that of C. macrorhynchos. In addition C. corone had a thicker gizzard wall than that of C. macrorhynchos, and the muscle layer of the C. corone gizzard was proportionately much thicker than that of C. macrorhynchos. It has been reported that although both species are omnivores, C. macrorhynchos is slightly more carnivorous, whereas C. corone tends towards herbivory. Our results suggest that the interspecific differences in stomach histology and morphology might be the result of these dietary differences between C. macrorhynchos and C. corone.

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We investigated the reproductive success of Mountain Hawk-Eagles Nisaetus nipalensis between 1990 and 2008 in Yamagata Prefecture, northern Japan. The existence of a correlation between fluctuations in Japanese Beech Fagus crenata seed production and nesting success was verified using observations of breeding attempts. A generalized linear mixed model (GLMM) was used to examine the relationship between nesting outcome and environmental factors (forest type, complexity of forest edges, nesting outcome in the previous year, and snowfall). To verify whether environmental factors affecting nesting outcome are influenced by variation in beech seed production levels, we analyzed the relationship between nesting outcome and environmental factors in the following three cases: (1) when beech seed production levels were high, (2) when beech seed production levels were low, and (3) when the beech seed production levels were not classified. Our results indicate that nesting success was significantly higher following a year when the level of beech seed production was high. However, the factor that was most strongly related to nesting outcome was nesting outcome in the previous year. In our study area, predominated by natural forest, when the beech seed production level in the previous year was low, GLMM analysis indicated that natural forest areas had a negative effect on nesting outcome, and artificial forest areas had a positive effect. The factors that affected nesting outcome differed depending on seed production levels in the previous year, and this suggested that the habitat used for hunting and/or the main prey species changed according to beech seed production levels.

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Previously only a winter visitor, the Daurian Redstart Phoenicurus auroreus was confirmed breeding in Fujimi-cho Nagano, in June 2010. A long-term investigation in the region confirmed that breeding continued in Fujimi-cho for four years, and by 2013 four pairs were established in Chino-shi and Shiojiri-shi. The Daurian Redstart is now considered to be breeding annually around Yatsugatake, and the breeding area is expected to expand in future. All of the nests were located within residential buildings at resorts or holiday cottage complexes.

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The wintering distribution of Rooks Corvus frugilegus has expanded considerably in Japan since the early 1990s, but their migration routes and breeding sites have not been described. We satellite-tracked the migration of 20 Rooks from the wintering area of the Hachiro-gata polder, northern Honshu, Japan northwestwards in spring. The Rooks departed Oshima, Tsugaru, and the Shakotan Peninsula in northern Japan, and arrived in the Sanjiang Plain in northeastern China, and the area east of Blagoveshchensk in southern Russia, which are suspected of being their breeding areas.

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Prey brought to an Oriental Honey Buzzard Pernis ptilorhynchus nest were recorded throughout the breeding season by means of a CCD camera system. Parents brought few food items during the courtship and incubation periods, but once the eggs had hatched prey consisted mainly of frogs and wasps, with the male bringing mainly hornets Vespa spp. and the female mainly yellow jackets Vespula spp.

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