The Black-footed Albatross Diomedea nigripes is an endangered seabird that is endemic to the North Pacific. The genetic structure of Black-footed Albatross populations on three of the Hawaiian Islands and on Izu-Torishima Island, Japan, has been studied previously, using the mitochondrial cytochrome b region. Hawaiian and Japanese breeding groups are genetically different, and the genetic diversity of the birds on Izu-Torishima is lower than that of birds in the Hawaiian Islands. We analyzed 50 Black-footed Albatrosses from the Bonin Islands, where a relatively stable population persisted throughout the twentieth century. Although albatrosses in the Bonin Islands do not differ significantly from those on Izu-Torishima in their cytochrome b region sequences, they do exhibit higher genetic diversity (as high as those from the Hawaiian colonies). A statistical parsimony network revealed two clades, one primarily in the western North Pacific colonies and the other primarily in eastern North Pacific colonies. The total network appears as a dumbbell-shaped phylogeny, suggesting recent population expansion in both populations, although the population breeding in the western North Pacific is only about 5% of the size of that in the eastern North Pacific. Our results suggest that Black-footed Albatrosses in the Bonin and the Hawaiian Islands differ genetically but are comparable natural biological units for conservation and management purposes.
It is necessary to correct plumage color fading when comparing the plumage coloration of birds captured at different times during the breeding season. We proposed two methods for correcting plumage color fading and compared them using the throat feathers of the Barn Swallow (Hirundo rustica gutturalis). One method uses the color shift of feathers on live birds during the same breeding season (the field method). The other method uses longitudinal color measurements of feathers placed on the open ground (the experimental method). This method has an advantage of not capturing the birds twice. The field and experimental methods estimated similar rates of fading of hue and brightness. Saturation was predicted to fade with time in the experimental method, which is unrealistic because there was no effect of time on saturation in live birds. Using the field method, we derived an equation for correcting plumage color fading in Barn Swallows. When assessing changes in plumage color, the field method should be used whenever possible since this method estimates plumage color fading in live birds.
The Common Kingfisher Alcedo atthis and the Greater Pied Kingfisher Ceryle lugubris breed sympatrically along the Chikuma River in central Japan. These kingfisher species differ in body size, with the latter being much larger than the former. To understand the potential mechanisms that might play a role in food-niche differentiation between these two species, we studied their foraging ecology in the breeding seasons of 2005 and 2006. Specifically, we compared the foraging habitat, foraging behavior, and food delivered to nestlings between the two kingfishers. We video-recorded the food delivered to nestlings during the day, and our results indicated that these species differed in their foraging ecology in several respects: (1) Common Kingfishers caught prey at sites where the water flow was calm, while Greater Pied Kingfishers hunted at sites where the water flowed rapidly; (2) Greater Pied Kingfishers dove from a higher position and caught fish in deeper water than Common Kingfishers; and (3) Common Kingfishers preferred smaller fish than Greater Pied Kingfishers. Overall, Common Kingfishers used a wider variety of foraging sites and food types than Greater Pied Kingfishers in the study area. As interspecific territorially and aggressive interactions between the two species were rarely observed, the food-niche differentiation between the two species was not likely the outcome of competitive exclusion. We conclude that the realized food-niches of the two kingfisher species reflect their respective body sizes.
We studied the morphological differences among breeding populations of the Arctic Warbler Phylloscopus borealis across the Far East and Alaska. We previously identified three strong monophyletic clades of the Arctic Warbler based on molecular phylogeny using mitochondrial DNA (cytochrome b): Clade A (Alaska, Anadyr, and Magadan), Clade B (Kamchatka, Sakhalin, and Hokkaido), and Clade C (Honshu, Shikoku, and Kyushu). To identify whether there are external morphological differences among these three mitochondrial clades, we used canonical discriminant analysis (CDA) and principal component analysis (PCA). CDA showed that the morphological differences among populations corresponded well with each mtDNA clade, with classification accuracies of 94.55%. In particular, populations of Clade C differed distinctly from Clades A and B in their longest natural wing and P10-PC lengths. The measurements of Clades A and B partly overlapped. In contrast, PCA enabled us to identify all individuals of each population correctly. Arrangement of populations in order of body size based on PC1 were Honshu>Kamchatka>Hokkaido/Sakhalin>Magadan/Alaska. We also found a latitudinal trend in body size and P10-PC lengths, which became smaller with increasing latitude. This trend in body size provides an example of reversed Bergmann's rule in birds. The latitudinal trend of P10-PC lengths may be related to migration distance. Our morphometric analyses suggest that the Japanese subspecies P. b. xanthodryas (Honshu and Kyushu) is readily identifiable based on measurements, whereas although the subspecies P. b. examinandus and P. b. borealis/kennicotti are also identifiable, some individuals of the latter two clades are similar in morphology.
Although the Northern Goshawk Accipiter gentilis is not designated a threatened species in Japan, it is thought that its population once experienced a decrease. To evaluate the current status of the goshawk, we sequenced the mitochondrial DNA control region and determined its variation among individuals. Considering that part of the Japanese population migrates or moves seasonally, we divided the samples into two categories (breeding and non-breeding season, based on sampling dates) and then calculated indices of genetic diversity and statistics for each category. Among 145 samples, we found ten haplotypes, of which two were dominant in both frequency and range. Haplotype diversity and nucleotide diversity were 0.63±0.04SD and 0.0018±0.0014SD, respectively. Comparing this diversity with those of other species, we concluded that the status of the Northern Goshawk in Japan is neither urgent nor secure. Significant genetic distance was not detected between the breeding and non-breeding groups, thus we could find no evidence of seasonal movement. The long-term effective female population size was estimated at 3,000 to 30,000 individuals. A recent population decline was not detected from the mismatch distribution. Therefore, the past population decline of the goshawk may not have been very serious. Future studies should consider the genetic structure of goshawks that inhabit other areas near Japan.
The full song of the Grey Thrush Turdus cardis consists of a ‘whistle part’ and a ‘trill part’ though a song bout usually consists of full songs and whistle-only songs (previous study). To clarify the importance of trills, two field experiments were conducted, a playback experiment with thirteen males and a female removal experiment with three males. The males continued singing the same number of songs before, during, and after playback. However, the males changed their song structure. They decreased the number of whistle-only songs and increased the number of trill-only songs during playback. Trill-only songs were thought to be delivered with aggression toward other males. Observations suggested that full songs were also delivered with aggression in the direction of other males. In the removal experiment, all three males increased song production dramatically when their mates were removed. The proportion of full songs was higher than before and after removal in all three males. Males were observed uttering trill-only songs while approaching their caged mates just before release. The current field experiments demonstrate that songs including trills have important roles in both intra-sexual aggression and pair formation.
The Japanese Murrelet Synthliboramphus wumizusume breeds in the Japanese islands. Murrelets have been observed around their breeding islands only during the breeding season. Their distribution and ecology during the non-breeding season are not known because the birds are not seen outside the breeding season. I confirmed the presence of several juveniles and adults in the western Seto Inland Sea. There are no previous records of Japanese Murrelets in this area, as the habitat was thought to be unsuitable. The current study provided the first observations of groups of juveniles and the first observation of adults outside the breeding season. The western part of the Seto Inland Sea was therefore confirmed as the habitat of non-breeding Japanese Murrelets. The observations provide information on the ecology and foraging habitat of the Japanese Murrelet during the non-breeding season. This should be valuable when considering ways of conserving the species.
Birds are potential dispersal agents of land snails by internal passage through the alimentary canals, such as plant seeds. Thus, we investigated whether snails are found in bird feces and checked damage to them in the oceanic Bonin Islands. Thirty individuals of five land snail species were found in 79 feces samples of Japanese White-eyes (Zosterops japonicus) and Brown-eared Bulbuls (Hypsipetes amaurotis). Two aquatic snail species were also detected in feces of Blue Rockthrushes (Monticola solitarius). Most of the shells remained unbroken, while the bodies were partly melted. When conditions were adequate, snails might be dispersed alive through bird guts.
The transition patterns of syllables (syntactical complexity) in songs of the Black-browed Reed Warbler (Acrocephalus bistrigiceps) were more complex than previously measured in the domestic bird, the Bengalese Finch (Lonchura striata var. domestica). Syntactical complexity was correlated with song duration (song length), which implies that these song characteristics have a similar function, probably in sexual selection. Syntactical complexity was not correlated with repertoire size (the number of syllable types), which is another presumable sexually selected trait but may not be important in this species, as previously suggested. Future studies on birdsongs should focus on not only repertoire size but also syntactical complexity.