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.

抄録全体を表示

小笠原諸島の固有種,メグロApalopteron familiareは,1958年以降ミツスイ科に分顔されているが,これまでにヒヨドリ科,メジロ科,チメドリ科などにも分類されており,分類学上の位置が不安定な鳥である.われわれはミトコンドリア12SリボソームRNAをコードするDNAの塩基配列に基づく分子生物学的手法により,メグロがメジロ科の1種であることを示す証拠を得た.また,メジロ科の中では,マリアナ諸島南部に生息するオウゴンメジロCleptornis marcheiに近縁であることを明らかにした.オウゴンメジロもかつてはミツスイ類とされていたが,最近,DNA-DNAハイブリダイゼーション法や生態•行動研究などによってメジロ類であることが判明した鳥である.メグロは,相互羽づくろいや接触就眠を行なう,巣づくりから育雛まで雌雄で行なう,求愛給餌を行なわない,などの生態,行動面でもメジロ類に似ている.また小笠原諸島には元来メジロ類は分布しないことになっているが,メグロがメジロ類の1種になることで分布のこの奇妙な空白も埋まることになる.

抄録全体を表示

1.カヤクグリの性判定の有効な指標を見いだすため,複数部位の外部形態測定値と総排泄腔突起の形態を調べた。
2.1989-1990年と1992年の5月20日から6月15日の期間,乗鞍岳山頂部において,すでに性のわかっている雄58個体と雌36個体について8部位の形態を測定した。
3.雄は雌に比べ体重は重く,翼長と尾長は長かったが,いずれもデータの分布にかなりの重複があるため,性判定の指標にはならなかった。5箇所の骨格部位(〓蹠,嘴峰の3部位および全頭長)には雌雄間に有意な差は認められなかった。
4.雌雄の総排泄腔突起の形態の違いが最も有効な性判定の指標であることがわかった。雄は繁殖期に輸精管の末端の肥大によるこぶ状の総排泄腔突起を形成し,雌は円柱状の突起を形成した。
5.雌雄の総排泄腔突起は繁殖期のみ発達していたので,総排泄腔突起による性判定は繁殖期に限定される。
6.カヤクグリの雄は,スズメ目の他種に比べ相対的に大きな総排泄腔突起と精巣をもっていた。雄の大きな生殖器官は,本種の一妻多夫あるいは多夫多妻の配偶関係から予想される強い精子競争に起因すると考えた。

抄録全体を表示

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.

抄録全体を表示

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.

抄録全体を表示