Nakanokami-shima was designated a national monument in 1972 because of its important for breeding seabirds, though the seabirds of the island were very poorly known. In this paper we present the information on the breeding species and their current status. Observations were made over a ten years period from 1975 to 1984.
Seven species of seabirds were found to breed on the island. All were summer visitors, except for the Brown Booby which may be a resident.
1. Bulwer's Petrel, Bulweria bulwerii. Bulwer's Petrel was not known to breed on the island until we captured and ringed 2 adults on 2 July, 1981, both of which had fully grown brood patches, and 2 more adults on 4 July, 1982, both of which were incubating. In 1982, 1983, and 1984 the petrels bred at the same locations shown in Fig. 1. The petrels bred gathering in small numbers and laid under rock, Sixty-six adults were ringed from 1981 to 1984 and it seems that the breeding population is fewer than 100 birds.
2. White-faced (or Streaked) Shearwater, Calonectris leucomelas. Many nest holes of the White-faced Shearwaters were widely distributed on gentle slopes in grassplateau in the centre of the island. Some birds incubated on bare ground under dwarf 'Gajumaru', Ficus retusa, and others incubated under large rocks. We could not estimate their population.
3. Brown Booby, Sula leucogaster. The main colonies, which were used by almost all the birds, were found annually at areas A, B, C, and D shown in Fig. 2. On Nakanokami-shima Brown Boobies nested on ridges and on steep cliffs. Few birds nested in the rocky zone near the shore. Before noon on 3 July, 1981, a Maritime Safety Agency Helicopter flew over the eastern part of the island, surprising the settled birds and causing them to take flight one after another. It was possible at that time to make a total count and 250 birds were counted. Since the breeding pairs were taking care of chicks at that day, some parents were probably absent offshore. Clearly the population was larger than 250. A chick ringed on 29 June, 1980, at the main colony was recaptured at the same place on 21 August, 1983. The bird was in adult plumage, but was not breeding. This recovery record indicates that non-breeding immatures are also included among those attending the main colonies. Table 1 shows the results of an intensive search for nests during the breeding season of 1984. Nests on inaccessible cliffs in areas A-D were of course omitted. The annual breeding population was estimated approximately as about 200 to 500 birds.
4. Red-footed Booby, Sula sula. This species was not known to breed in Japan before 1975, when we discovered a breeding pair on 27 August, 1975. The parent incubated one egg and its nest was builted on the canopy of dwarf 'Gajumaru' bush in area A in Fig. 2. On 24 June, 1976, 3 adults and 2 chicks were ringed at the same place, and on 30 June, 1977, one downy chick and parent were found again at the same place as in 1975. On 13 July, 1982, two fledglings and one adult were seen on the cliff in area E in Fig. 2.
5. Bridled Tern, Sterna anaethetus. This, species was not known to breed in Japan until we found its breeding at the island on June, 1980. The Bridled Tern settled rocky zone near the shore, placing their eggs in the shelter of rocks. The locations of colonies in 1983, and 1984 are shown in Fig. 3. This tern is apparently an inshore feeder, remaining usually close to the colony. The estimated numbers were 120 birds in area A, and 40 in area B on June 30, 1980, about 1000 in area A, and 100 in area B on 2 July, 1981, and about 650 in area, A, and 50 in area B on 2 July, 1982. Since 1981 the numbers have increased markedly. The birds in attendance at these areas were in adult plumage, however considerable numbers of non-breeding, presumably immature, birds may make up part of these totals.

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1.1981,'82,'83年に仲の神島で繁殖するセグロアジサシの個体数を主に写真撮影によって算出した。
2.各年の主副集団営巣地はFigs.1,2,3のように形成されていた。
3.各集団営巣地に日中留まっていた成鳥数はTable 1に示すとおりであった。
4.抱卵期から育雛前期の繁殖段階では,写真撮影時に営巣地に日中留まっていた成鳥は番の雌雄のどちらか1羽だけであると仮定し,さらに,日中留まっていた全成鳥数のうち非繁殖鳥の割合は僅少であると仮定すると,営巣地に日中留まっていた成鳥数は番数にほぼ等しい。
5.この仮定によれば,1981,'82,'83年における仲の神島のセグロアジサシの総繁殖番数は,それぞれ約6400番,4100番,3000番と推定された。
6.副集団営巣地(Table 1およびFig.1中の地区1-6と10-14)におけるこの3年の繁殖番数は約500-600番でほぼ一定していたが,主集団営巣地(地区7,8,9)における繁殖番数は,1981年には約6000番,1982年には約3500番,1983年には約2500番で年による変化が大ぎかった。
7.この年変動の要因は,同地域の全面積の約30%を占める中央部分の地表が1982年と1983年の繁殖初期に草類で被われていたために,本種の営巣には不適であったことと,新たな営巣地の拡大も営巣密度の増大も生じなかったことであろう。
8.1982年には,主集団営巣地について1番当りの雛(幼鳥)の生産率を推定した。8月9日に来襲した台風11号による被害を受ける前の8月初めでは,生産率は約0.60,8月下旬では約0.51であった。

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(1) 1982年8月9日,中型の強い台風11号が仲の神島をほぼ直撃する進路をとって北上した(Figs.1-4)。台風通過後9日目の8月18日に台風による被害調査を行ったところ,Table 1に示すように,繁殖中の4種の海鳥類の死体を発見した。
(2) セグロアジサシについては,台風来襲前後の繁殖状況調査,標識鳥の死体回収,主副集団営巣地の台風後の状況などから,台風来襲直前に棲息していた幼鳥の少なくとも10数%以上がこの台風で死亡したと推察される。
(3) 主に海岸線の岩石累積地帯で営巣しているマミジロアジサシとアナドリの繁殖は壊滅的な被害を受け,主に崖地や岩棚で営巣しているカツオドリとクロアジサシも相当な被害を受けたであろう。

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既報の如く,1974年バフ変ハシブトガラスが皇居内で発見され,1977,'78年,約1km離れた赤坂でなわばりを確立したが,繁殖は確認されず姿を消し,1981年,そして今回1986年に単独で再出現し,他の同類に排斥されるのがみられた。以上を同一のバフ変個体とみると,繁殖まで3～4年,繁殖行動2年間,以後は単独放浪したらしく,12年目まで生存が確認された。これが正常個体でも同様であるかは,今後の研究に待つ。

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