Diurnal gulls and skuas, which depend mostly on visual cues during kleptoparasitic attacks, experience reduced predation success when low light conditions or dense vegetation impair prey visibility. Rhinoceros Auklets Cerorhinca monocerata lose prey to kleptoparasitic conspecifics and kleptoparasitic gulls. The return of adult auklets to their colony was observed and incidences of inter- and intra-specific kleptoparasitism were recorded in five study sites with high and low vegetation coverage under variable conditions of illumination. Whereas gulls (Black-tailed Larus crassirostris and Slaty-backed L. schistisagus) mainly attacked auklets in flight in the early evening and from distances exceeding five metres, auklets attacked later in the evening after auklet numbers on the ground had increased, and only when closer than two metres. Intra-specific kleptoparasitism occurred less frequently in sites with dense vegetation and where the visible range was short. These findings indicate that environmental factors facilitating kleptoparasitism among gulls (aerial pirates) and auklets (close-quarter terrestrial pirates) are different.

抄録全体を表示

Like most seabirds Streaked Shearwaters Calonectris leucomelas have sexually monomorphic plumage. Researchers have conveniently identified gender in the field by means of two types of calls, associated with dimorphism in body size. By molecular sexing analysis using the chromo-helicase-DNA-binding (CHD) genes, we determined the gender of Streaked Shearwaters in relation to call types and body size. We recorded the type of calls, measured body dimensions and collected non-invasive samples (buccal cells or feathers) of Streaked Shearwaters at two breeding islands. As obvious amplification to identify gender by polymerase chain reaction (PCR) could not be obtained at high rates using a known universal primer pair, we developed two new primer pairs to identify gender in this species; this enabled us to identify the gender of all of the samples. Without exception all males gave high-pitched calls, whereas all females gave low-pitched calls. Molecular evidence also confirmed morphometric differences between males and females. We, therefore, conclude that Streaked Shearwaters exhibit sexual dimorphism in body size and call type. Males are significantly larger than females, and males give high calls whereas females give low calls.

抄録全体を表示

Glucocorticoids mediate various essential biological functions by binding to and activating their specific receptors. In vertebrates, interactions between glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) play an important role in the feedback pathways of glucocorticoid regulation. In free-living birds, a number of studies have demonstrated seasonal regulation of the adrenocortical response to stress, but little is known about their downstream receptors, GR and MR. In this study, we successfully cloned the full-length open reading frames (ORFs) of the GR (eGR) and the MR (eMR) cDNAs from a passerine species, the Eurasian Tree Sparrow Passer montanus. The ORFs eGR contains 2,322 base pairs encoding 773 amino acids, and the eMR contains 2,952 base pairs encoding 983 amino acids. The eGR and eMR are highly conserved in their gene and amino acid sequences and in their secondary and 3D structures when compared with other species of birds and vertebrates.

抄録全体を表示

To examine the population trends of grassland and shrub birds in Hokkaido, we conducted line transect censuses in 2002 and 2003, in area where avifaunal studies had been performed in the 1970s and 1980s. To document the decline in the Yellow-breasted Bunting Emberiza aureola, birdwatching data were also analysed. The Yellow-breasted Bunting population has decreased drastically both in density and in distribution over the intervening thirty years. The decline in occupied breeding sites and in the population is continuing. Densities of Eurasian Skylark Alauda arvensis and Lanceolated Grasshopper Warbler Locustella lanceolata have also declined, although their range contractions are not yet severe. The ranges of Brown Shrike Lanius cristatus and Chestnut-eared Bunting E. fucata appear to have contracted. In contrast, data analysis revealed that the breeding range of Yellow Wagtail Motacilla flava has expanded in northern Hokkaido, but it is possible that the range had expanded in the past but had been overlooked. The present study suggests that the ranges of Bull-headed Shrike L. bucephalus and Gray's Grasshopper Warbler L. fasciolata had expanded, although some previous studies do not support this trend. In this study we were not able to clarify the reason why the population trends of these species have changed. Further research is necessary focussing on: breeding habitat analysis, breeding biology in relation to population trends, population trends in wintering and migration areas and clarification of migration routes. The population decline in the Yellow-breasted Bunting is both dramatic and very severe. This migratory species in particular requires immediate international conservation measures to avoid national and regional extinction.

抄録全体を表示

Introduced mammals may have deleterious effects on avifauna. We investigated whether such species may be affecting the breeding success of the critically endangered Amsterdam Albatrosses Diomedea amsterdamensis on its remote breeding island. Twelve camera-traps deployed near albatross nests during the chick brooding period in 2011 captured 25,000 pictures. Two of them showed Black Rats Rattus rattus, but without revealing evidence of any direct interaction between the two species. Breeding success in 2011 was similar to that in previous years (60%). Our survey suggests that introduced mammals may not currently represent a primary direct threat to this population, but they might amplify the risks of chick mortality in case of disease outbreaks.

抄録全体を表示

The Red-billed Leiothrix Leiothrix lutea has been introduced to, and become established in Japan, the Hawaiian Islands and certain areas of Europe. Unlike in its native range, introduced Red-billed Leiothrix populations have not been observed to be hosts of avian brood parasites. We found a parasite egg with three host eggs in a Red-billed Leiothrix nest on 14 July 2010 on Mt Tsukuba, central Japan. Despite its marked difference from the host eggs, the parasite egg was accepted and incubated by the l Red-billed Leiothrix parent until the nest was depredated before hatching. The morphology of the parasite egg suggested that it belonged to Oriental Cuckoo Cuculus optatus.

抄録全体を表示