Most North American bird species that are less successful in small forests than in large forests, are forest-interior specialists that winter in the tropics. These species have declined in small forests because of high rates of nest predation and brood parasitism near the forest edge. To determine whether migratory forest-interior specialists are also important components of bird communities in Japan, we surveyed bird populations on plots at the edge and in the interior of deciduous forests in Hokkaido and Kyoto. Surveys were conducted during the breeding season in forest fragments using the point count method. We calculated edge indices for the most abundant species in Hokkaido and Kyoto (38 and 18 species, respectively). Among the nine species that were more abundant in interior than in edge plots in Hokkaido were the following tropical migrants: Turdus cardis, Phylloscopus coronatus, and Cuculus saturatus. In Kyoto, the abundance of particular species of tropical migrants was too low to permit statistical analysis. We therefore analyzed the rare species as a group and this group was more abundant in the forest interior than on the forest edge. Three resident species, Garrulus glandrius, Picus awokera, and Bambusicola thoracica, were also more abundant in the forest interior. The most frequent potential nest predator, Corvus macrorhynchos, was more abundant at the edge than in the interior in Hokkaido, but showed the reverse pattern in Kyoto. The abundance of the most frequent brood parasite in Hokkaido, Cuculus saturatus, had a weak positive relation with the abundance of its host species, but was not significantly related to the distance from the forest edge. Therefore, the major negative edge effects in Japan may be due to nest predation by corvids. The impact of negative edge effects, as well as the effect of forest structure, on forest-interior birds in Japan should be the focus of future research.
We investigated a convenient method for estimating the absolute density of breeding populations of a threatened subtropical passerine, Apalopteron familiare, which is endemic to the Ogasawara (Bonin) Islands. In order to estimate the number of breeding males or pairs, the method takes advantage of the brief dawn chorus period of the species. The number of vocalising males detected, using the method, was very stable during each census period. The detectability of resident males was nearly 90% of the total number of resident males known to be occupying the study area, based on territory mapping of marked birds. Only about 10% of resident, paired males did not sing, thus the method registered almost all males singing in the study site. As few unpaired, singing males were present, the number of males estimated by the method was approximately the same as that of paired males.
We measured the flight speed of Short-tailed Shearwaters (Puffinus tenuirostris) in Tsugaru Strait, northern Japan, using ship-loading radar. When sea conditions were calm, estimated flight speed and direction were unaffected by wind. The average flying speed was 14.3±1.63 (SD) m/s (n=7), with a range of 12-16m/s. Based on the above results, we calculated the theoretical values of Vmp (minimum power speed) and Vmr (maximum range speed), presented by Pennycuick (1975, 1987). The results were Vmp=9.74m/s, and Vmr=16.18m/s. Flight speeds estimated using radar were near the Vmr, suggesting that the Short-tailed Shearwaters observed in Tsugaru Strait during late April were on migration to northern sea areas.
Breeding of the Eastern Marsh Harrier (Circus spilonotus spilonotus Kaup 1847) was confirmed in the area along the Ishikari River in the Ishikari District, Hokkaido, Japan. Among the eight nests discovered during the 1988 breeding season, eggs were observed in three nests, and chick (s) were confirmed in three other nests. The remaining two nests had no eggs or chicks. One might have been examined before eggs were laid, and the other might have been abandoned. In addition, two other sites were considered to be probable breeding sites, though the nests could not be found. Breeding processes were not pursued because the confirmation of breeding was the main purpose of this investigation. It was noteworthy that two nests had been built of bamboo grasses on the ground amongst dwarf bamboo. The other six nests were built of reeds in reed marshes as is generally known.
The impact of oil pollution on seabirds has been widely reported in the ornithological literature. We reviewed the world-wide mortality of seabirds resulting from oil spills occurring from the 1960s to the present. Oil spills were classified as either 1) accidental, or 2) chronic. Among accidental oil spills from ships, oil terminals or pipelines, oil spills from ships were the commonest, with 43 events. Following the increasing use of supertankers for oil delivery, the spill volume from recent accidental spills sometimes outweighs the total annual spill volumes recorded during the 1970s. The spill volume of an event is only weakly correlated with the degree of impact on seabirds, as has previously been reported, because depending on the time of the year and the location, even a small amount of oil can have a great impact on seabirds, as was the case along the Norwegian coast in 1979. A few studies have estimated the total numbers of seabirds dying by taking into account the proportion of carcasses that sink, and the persistence rate of carcasses along coasts. Many studies have claimed that determining the impact of oil spills on seabird populations is fraught with difficulties, unless information on pre-spill status is available for targeted populations. Sources of chronic oil pollution include the discharge or dumping of oil polluted water or waste oils from ships, oil tanks or pipelines. Although chronic oil pollution has the potential for having serious impacts on seabird populations, it receives far less public attention than conspicuous accidental oil pills. For example, 7, 735 seabird carcasses were retrieved after the tanker Esso Bernicia spilled near a North Sea oil terminal in 1978, but more than half of these birds had actually died as a result of oil contamination from a chronic spill, and not as a result of the tanker spill. Beached bird surveys, and analysis of oil chemical composition attached to carcasses and beaches have played an important role in recognising the occurrence of chronic oil spill events and determining the source of the oil and, in some cases, in assessing their impacts on seabirds. In order to evaluate the areas, or seabird populations that are vulnerable to oil pollution, basic information on the distribution and ecology of each seabird species is also required. Such information has been lacking, especially for the seabirds that inhabit the seas around Japan. To help seabird populations recover after oil spills, it is necessary to remove those factors preventing a particular population from recovering, such as bycatch at sea, predation at the breeding ground and/or by making improvements to the breeding habitat.
In January 1986, an oil spill occurred in the Japan Sea. The oil spread 400km along the coast from Shimane Prefecture to Fukui Prefecture. The spill affected a large population of migrating seabirds in Shimane and Tottori prefectures. Among the 1, 761 seabirds mostly counted dead in Shimane Prefecture during late January 1986, about 93.5% were Alcidae. The species most seriously affected was the Rhinoceros Auklet Cerorhinca monocerata, with 1, 326 (75.3%) recorded. The second most seriously affected were Synthliboramphus spp., with 320 (18.2%) victims. Twelve ringed Cerorhinca monocerata were affected, 11 of these had been ringed on Teuri Island, in the northern part of the Japan Sea, off Hokkaido, and one originated from Ashi Island in the Pacific Ocean off northern Honshu.