Reproductive behaviors of the male bird, such as aggressive and sexual behaviors, are considered to be the typical instinct behavior and have been studied anatomically, ethologically, and endocrinologically. Since the electrical stimulation of the hypothalamus and preoptic area can elicit stereotyped reproductive behaviors in several avian species, these brain regions are considered to be involved with the control of male reproductive behaviors. The occurrence of a variety of reproductive behaviors shows a seasonal variation in most species of wild male birds inhabiting the temperate zone. Behavioral studies combined with endocrinological methods showed that sex steroids released from the testis, particularly testosterone, are essential to produce male reproductive behaviors in several temperate birds including the Japanese quail. One of the targets of testosterone is the preoptic and hypothalamic neurons, because testosterone or its metabolites concentrating cells was shown in the medial preoptic area, nucleus paraventricularis, regio lateralis hypothalami, nucleus inferior hypothalami, and nucleus infundibuli in the Japanese quail as well as other avian species. In addition, androgen actions in the avian brain are often mediated by the enzymatic activity that catalyzes the conversion of androgen to estrogen. Both aromatase and estrogen receptors are present in several brain regions including the hypothalamus and preoptic area. Thus, the reproductive behaviors of male birds are rather well understood in ethological and endocrinological terms.
In contrast, little is known regarding the cellular and molecular regulations on the central nervous system of these behaviors. Neuropeptides are supposed to be implicated in the regulation of hormone dependent behavioral processes in birds. Recently, we have isolated three opioid peptides, i. e., Met-enkephalin, Leu-enkephalin, and Met-enkephalin-Arg-Phe, from adult males of the Japanese quail and zebra finch. On the basis of immunohistochemical studies, these enkephalins were located in the preoptic and hypothalamic areas as well as other brain regions. A series of our experiments indicated that their main physiological functions in these areas is an inhibition of neuronal activities. Thus, opioid peptides may regulate some reproductive behavior through the mechanism that provokes such an inhibition. On the other hand, new findings that neurosteroids accumulate in the brain through mechanisms at least partly independent of peripheral steroidogenic glands have been available in an avian species. We have recently demonstrated that the avian brain produces pregnenolone, the main precursor of steroid hormones, on the basis of biochemical studies. Furthermore, the immunohistochemical and Western immunoblotting analyses showed that a specific enzyme of the pregnenolone synthesis, cytochrome P450scc, is located in the preoptic and hypothalamic areas in addition to other brain regions. The distribution of this enzyme suggests that pregnenolone acts as an important neurosteroid to regulate the avian reproductive behavior.
This paper summarizes the advances made in our understanding of regulatory mechanisms of the avian reproductive behavior.

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Since 1958, Apalopteron familiare has been placed in the Meliphagidae and called the Bonin Islands Honeyeater or Ogasawara Honeyeater. Previously it had been treated as a bulbul, a babbler, a sylviid warbler and a white-eye. Here we present 12S rRNA sequence evidence that shows that Apalopteron is a member of the white-eye family Zosteropidae, closely-related to the Golden White-eye (Cleptornis marchei) of the southern Mariana Islands, which was also misidentified as a honeyeater until its true affinities were revealed by field observations and DNA-DNA hybridization. The ecology and behavior of Apalopteron and Zosterops are compared and reviewed. The English name Bonin Islands White-eye is proposed for Apalopteron familiare.

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External morphological measurements and the characteristics of cloacal protuberances were investigated to find a useful index of sexing the Japanese Accentor Prunella rubida. From 20 May to 15 June in 1989-1990 and 1992, morphological variations in eight characters were measured in known-sexed 58 males and 36 females inhabiting on the top of Mt. Norikura, Japan. The males were significantly heavier and had longer wings and tails than females, but these measurements could not be used as indexes for sexing because there was still considerable overlap. No sex-related difference in size was evident in the five skeletal elements monitored (tarsus, three bill dimensions and head length). The sharpness of the cloacal protuberance of each sex proved to be the most useful index to identify the sex of individuals. The males developed a nodular cloacal protuberance formed by the growth of the distal ends of sperm-filled ductus deferens, while the female's cloaca protruded from its original position to form a cylindrical protuberance. Because the cloacal protuberance of each sex developed only during the breeding season, its use as a characteristic for sex is confined to the breeding season. Male Japanese Accentors had a relatively large cloacal protuberance and testes compared with other passerines. It seems that these large reproductive organs are linked to the intense sperm competition predicted from this species' polyandrous or polygynandrous mating combination.

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Breeding of European Hobby Falco subbuteo was observed in Nagano City (L355, N36°8'8" E138°12'24") for the first time. The old nest of crow sp. on an iron pole in a golf training field was used. On June 25, 1994, female began to sit in the nest. On July 28, chicks were fed for the first time. On August 3, two chicks and one egg were confirmed. A chick was fledged on August 29 and another on August 30. This report forms the southernmost breeding record of European Hobby in Japan.

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A flock of Oriental White Storks appeared in Yonaguni Island, the westernmost Japan in November 1993. The flock size at the time was eleven. The communal roost that was formed in a lowland valley with paddy field seems to have been shifted to another paddy field area during a short period in March 1994, probably due to human disturbance at the former place. Another important habitat for storks was pasture where they foraged. The flock of eleven storks were never recorded after December, but it is highly probable that the eleven birds overwintered in the island, since roosting of a single bird apart from the communal roost with ten birds was suggested for a night in February. Large flocks at the communal roost were recorded last on 19 March and thereafter one or two storks were witnessed until the summer of the year.

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