Six cases of bigamous trios in the Black-winged Stilt Himantopus himantopus himantopus were studied during 1997-2006. One cause for the occurrence of bigamous trios is that postbreeding groups composed of a parent and a female offspring of the previous year, or that of a family and an unrelated female, have not dissolved by the next breeding season. Under conditions of a female-biased sex ratio in the non-breeding season, some females may chose bigamous trios as one of three mating options. In one trio, one female left the trio just before egg-laying, after they began to defend the nesting territory. Two bigamous trios made a joint nest, respectively. One bigamous trio made two simultaneous nests. One bigamous trio made a joint nest in one year and two simultaneous nests the following year. One bigamous trio made three nests successively.
The relationship between the song repertoire and breeding success of birds has been studied for several species. In some species, the different components of the songs have different functions and are suggested to have evolved under different intra- and intersexual selection pressures. The song of the Grey Thrush Turdus cardis consists of the whistle and trill parts. In this study, it was clarified that the repertoire sizes of the syllables in both parts did not correlate with each other, suggesting the possibility that both parts have evolved under different sexual selection pressures. The repertoire sizes also did not correlate with the age of the birds. The relationship between the repertoire size and the mating status of males was also examined. The whistle repertoire size was not related to the mating status, while the trill repertoire size in polygynous males was larger than that in monogamous males. This result suggests that the functions of the two parts of the song are not similar, a finding consistent with the results of previous studies indicating that the complexity of trills has evolved under intersexual selection pressure.
Generally, it has been considered that the Ural Owl Strix uralensis feeds mainly on small birds, amphibians and small mammals such as voles, and only rarely on insects. However, we found that the Ural Owl often preys upon the Japanese horned beetle Trypoxylus dichotomus septentrionalis, which has never before been reported as an insect prey species for the Ural Owl. We here demonstrate that Ural Owls at the present study site frequently prey upon Japanese horned beetles for a limited period during summer. Details of the predatory behavior of Ural Owls upon beetles are also given.
The difference of migration timing during the autumn migratory period of three leaf warblers of the genus Phylloscopus, breeding widely in Japan, was studied at two areas of Honshu Island, Japan; Nobeyama plateau in Nagano Prefecture, central Honshu and Mt. Rokko in Hyogo Prefecture, about 340 km west-southwest from Nobeyama plateau. The three species of leaf warbler were captured by mist-net from late July to early or late November over a five year period (2003-2007). The Eastern Pale-legged Leaf Warbler Phylloscopus borealoides and the Eastern Crowned Leaf Warbler P. coronatus were captured almost exclusively from late July to early September, whereas the Arctic Warbler P. borealis was captured from early September to late November. The trapping period of the former two warblers overlapped greatly, but the median period of the Eastern Pale-legged Leaf Warbler was earlier than that of the Eastern Crowned Leaf Warbler at Mt. Rokko. The slight overlap of fall migration timing between the Arctic Warbler and the other two warblers may be related to the latitude of breeding ranges of the respective warbler species.
The breeding season of the Great Tit Parus major is divided into two periods: the early and late seasons. In the early breeding population, the number of pairs varied from 45 to 152, with an average of 102±24 SD. In comparison, the late population was smaller than the early population every year and varied from 30 to 95, with an average of 54±18 SD pairs. Half of the early breeders were adult breeders from the previous year, and most of the remaining breeders were young belonging to winter flocks in previous years. The late breeding population consisted mainly of pairs that were producing their second brood that season, and repeat breeders whose first brood had failed. The proportion of adult male and adult female pairs was higher than other pairs. Most pairs were faithful, but divorce occurred every year. The population also included some pairs that did not breed and single males. The longevity was nine years in males and seven years in females.
A mapping technique was used to census House Sparrows Passer domesticus in different urban environments, defined by housing density, housing age and proportion of ‘green’ area, in a small town in NE England. The study was conducted during the breeding season, with the aim of identifying the parameters that influence breeding density. Maximum House Sparrow density occurred in areas with high housing density, including the town centre, but a decline in numbers over the last 10 years was apparent in suburban areas with intermediate housing density. An area with low housing density was abandoned by House Sparrows in 1980, and a new housing estate completed in 2002 has not been colonized.
The Black-naped Tern Sterna sumatrana and Roseate Tern S. dougallii are inshore breeders on the Ryukyu Islands, Japan. Monitoring surveys are an important tool in conservation measures for these species, yet it is essential that disturbance to breeding caused by entering into tern colonies is minimized. Based on our long-term studies of the breeding ecology of these two species, we suggest methods of counting of the nest number and estimating the egg laying period based on estimated age of chicks derived from observations made outside the colony. The minimum number of nests can be assessed by counting the number of adults sitting on nests, and the number of chicks out brooding by parents, or fledglings. The hatching date can be estimated by observation on characteristics of their figure and behaviors. The egg laying date can be back-calculated based on the incubation period, which averages 24 days for the Black-naped Tern and 23 days for the Roseate Tern. Furthermore, it is possible to compare the timing of the start of the egg laying and that period between colonies. It is desirable that more than one researcher divide the breeding sites and conduct the above survey on each breeding sites at the same time.
In 1993, a new breeding ground for the Short-tailed Albatross Diomedia albatrus was established at Hatsunezaki, on Torishima, Izu Islands, using decoys and sounds. In 1995, the first pair to succeed in nesting and laying an egg there was recorded. Since 2004, the number of breeding pairs increased gradually and a new breeding ground was established. The total number of estimated pairs present at the new breeding ground was strongly correlated with the actual number of pairs that subsequently bred there.
In 2005, we surveyed the birds inhabiting the Tokyo University Forest in Chichibu, in western Saitama Prefecture, Japan. Special attention was given to the Bush Warbler Cettia diphone, which appeared at the study site after 22nd March. We captured seven male Bush Warblers and banded them with individually unique combinations of color rings. Six males of them maintained the same home ranges (territory) throughout the study period, and no other males were observed. The population density of the males was 19.2 individuals per km2. Although we were unable to locate an active nest to study the breeding and rearing process, juveniles were captured in August. The tarsus length of juveniles reached the size of adults earlier than the natural wing length. Thus, in the juveniles, sexual size dimorphism was evident in the tarsus length to the same extent as seen in adults. We found nests of the Japanese White-eye Zosterops japonicus, Long-tailed Tit Aegithalos caudatus, Short-tailed Bush Warbler Urosphena squameiceps, Blue-and-white Flycatcher Cyanoptila cyanomelana and Red-billed Leiothrix Leiothrix lutea. The clutch of the Short-tailed Bush Warbler was believed to have been parasitized by the Oriental Cuckoo Cuculus saturatus. We confirmed that 40 species of birds occurred in the study area during the study period.
A Little Bunting Emberiza pusilla was captured and banded at Funatsu, Kihoku-cho, Kitamuro-gun, Mie Prefecture (34° 07′ N, 136° 13′ E) on 31 October, 2007. Judging from the condition of the tail feathers, this individual was in first winter plumage. This is the first authenticated record of this species in Mie Prefecture.
An Oriental Plover Charadrius veredus was observed at the Hachijo-jima Airport, Hachijo-machi (33°07′ N, 139° 47′ E) on Hachijo-jima, Tokyo from 2nd to 3rd May, 2006. In comparison with the Pacific Golden Plovers Pluvialis fulva that were presented nearby, this individual was slightly smaller, its legs were longer, and its bill was comparatively thinner and longer. The upperparts, including the head and the wing coverts, were pale brown. The supercilium was white and reached the forehead. The underparts were white and the breast was pale buff. This species has been recorded only in Ibaraki and Chiba Prefecture in the Kanto area and has never previously been recorded in Tokyo, including the Izu and Bonin Islands.