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.
During our surveys on Nakanokami-shima from 1975 to 1984, seven species of sea birds were recorded breeding. Among them, the Sooty Tern Sterna fuscata was probably the most abundant. Fig. 1 shows the locations of colonies of the species in 1981, 1982, and 1983. The photographs were taken from selected high points situated west and east of the main colony. Based on these photographs, the number of the birds which stayed on the colony in the daytime was counted; while the birds on subcolonies were counted through binocular. The results of counting are shown in Table 1. Attendant birds on early stage of breeding season were adult plumaged. Most of these birds remaining during the daytime seemed to be occupying nest sites, and it seemed that one bird of each pair stayed on the nest site while other bird was absent offshore. If the number of non-breeding birds, including immatures, was negligible, then the number of birds staying on the colonies in the daytime should be equivalent to the number of breeding pairs. On the above presumption, the breeding population of the main colony were c. 6000 pairs in 1981, c. 3500 pairs in 1982, and c. 2500 pairs in 1983. This remarkable annual variation is due to the fact that the centre of the main 1981 colony was covered with tall dead herbage in early 1982; and with well grown grass in 1983 (Fig. 2). The changes in the vegetation resulted in fewer pairs settling in the area. On the other hand, neither the apparent increasing of breeding density as a whole nor the expansion of colony did occure in 1982, and in 1983. In 1982, the number of fledgling in the main colony on 22 August was c. 1800; approximately 0.51 chicks per pair. However on 9 August, 1982, a strong storm (Typhoon-8211) had passed the island and 300 dead chicks were found in the main colony on 18 August. Therefore, the production of chicks per pair just before the accident was probably at least 0.60. The estimations of total breeding population in 1981, 1982, and 1983 were 6400 pairs, 4100 pairs, and 3000 pairs respectively.
Strong storms regularly pass the southern Ryukyu Islands from early summer to late autumn, however their influence on breeding colonies of sea birds in the region has not been studied. A mediumsized but strong storm, Typhoon-8211, passed Nakanokami-shima on 9 August, 1982 (Figs. 1, 2, 3, and 4). On the survey of 18 August, many dead and injured Sooty Tern chichs were found (Table 1). More than ten percent of all Sooty Tern chicks died. Apparently, the Bridled Tern and the Bulwer's Petrel bred in rocky shore would be inflicted destructively since high waves must rage on their colonies frequently, and also the Brown Booby and the Brown Noddy bred on the ledges of cliff seemed to be damaged so much by a strong rainstorm.
A schizochroismic Corvus macrorhynchos was found in 1974 (among group of young birds), spent territorial life during 1977 and 1978, paired with a normal bird, but breeding was not successful and the bird finally disappeared. It suddenly occurred again solitary in 1981 and 1986 (Jan. 4), and was chased by other crows. This may suggest a case of individual life history of this species, but may also be a special case owing to its abnormal plumage colour.