The Barn Swallow Hirundo rustica is a model species for studying sexual selection. After its long tail was shown to be the target of female mate choice, its plumage characteristics, including the red throat patch and the size of white tail spots in addition to tail length, have attracted the attention of many researchers. Although there have been several reviews of sexual selection in this species, these reviews have focused mostly on general patterns of sexual selection within and among subspecies, rather than on the functional differences between plumage characteristics in sexual selection. Here, I review mechanisms of sexual selection for male plumage ornaments in Japanese Barn Swallows H. r. gutturalis. In the last decade, studies of sexual selection in Japanese Barn Swallows have focussed on tail length, the size of the white tail spots, and the size and coloration of red throat patches. Each ornamental trait appears to be involved in different sexual selection mechanisms: the size of the white tail spots is important for several mechanisms of intersexual selection, including the Darwin-Fisher mechanism and differential allocation, whereas throat coloration may be intra-sexually selected, at least in part. The size of the throat patch, in contrast, is the target of an intersexual selection mechanism, differential access, indicating a partially independent evolution of the two components of the red throat patch. Multiple mechanisms of sexual selection would explain the multiple ornaments and their geographical variation, and even the probability of speciation and extinction.
Decline of biodiversity, especially in tropical areas and rainforests, due to human activity is a serious global issue. Recovery programs, including reintroductions, are one means of active species protection and biodiversity preservation. The Sumatran Laughingthrush Garrulax bicolor (SL), a little known passerine endemic to Sumatra Island, is currently suffering from serious population decline due to the intensity of the illegal wildlife trade and habitat loss in the region. Most local subpopulations have been extirpated and those remaining have been reduced, thus, urgent need for conservation has arisen. In this study, we carried out the soft-release of rehabilitated SLs, originating from the wild and kept in captivity. We released four SL pairs (N=8 individuals) in total and, by using radio-telemetry (VHF; <2 g tail-mounted tags); we assessed their survival rate and movement patterns. During the post-release period only one bird was monitored for the full, predetermined criterion period of three weeks for survival rate and site fidelity assessment and one death was confirmed directly. Affinity to the release site, defined by a 2 km radius around the release aviary, was lower for females, which left the release site within the first week after release leaving their fates unknown, compared with males which remained at the release site for up to three times longer. Therefore, only the males' home range sizes were calculated. As a standardised measure, only the first six days following release were included and 6-day home ranges were estimated as follows: 35.18±8.5 ha (mean±SE) with range 17.25–50.95 ha (N=4 males). We did not find significant differences in the distances of males from the release aviary with increasing days following release. As far as we know, this is the first field study providing novel knowledge of the recovery ability of the Sumatran Laughingthrush and of its post-release behaviour, which are crucial for species protection management.
In many passerines, reproductively active females must forage for calcium-rich materials on a daily basis to meet exact calcium demands during egg production. Calcium availability often constrains reproductive output in birds, but is dependent on species-specific foraging traits and local calcium availability, and, thus, land use. Here, we examined whether calcium availability limits the reproductive output of Green-backed Tits Parus monticolus over a four-year period in mid-altitude subtropical forest of Taiwan. We compared soil nutrients and the availability of calcium-rich snails between mixed-oak forest and Japanese cedar Cryptomeria japonica plantation. We also provided supplementary calcium (in the form of snail shells and chicken eggshells) in the nest boxes of half of all pre-laying pairs breeding in both habitats. The reproductive output of birds across the two treatments and two habitats was recorded. Our results showed that the soil was very acidic in both habitats. Compared to the mixed-oak forest, the litter in the cedar plantation contained marginally significantly more calcium, while the soil had significantly higher pH and exchangeable Ca2+. The cedar plantation supported similar, or even higher, snail abundance than the mixed-oak forest. We found no abnormal eggs with defective shells in either habitat. We also found no significant difference in clutch size, egg mass, egg shape index, egg volume, clutch volume, or hatching success across the two calcium-treatment groups or the two habitats. Calcium availability had a weak effect on the reproductive output of birds in the two habitats, possibly because the study area supported a high abundance of snails. Our results, combined with our calculations of the calcium demand of birds, suggest that calcium is not a limiting micronutrient for egg production by Green-backed Tits in the montane forest of subtropical Taiwan at present.
In Japan, geographic variation in bird song is known only on small peripheral islands with isolated populations, and has not been reported in any species on the main islands of Japan, probably due to the close proximity of the populations on the relatively small main islands. On Honshu, one of the four main islands of Japan, the Yellow Bunting Emberiza sulphurata breeds in restricted habitats (i.e. wet grasslands with forest edge, or wet grasslands with sparse forest). This may facilitate the isolation of its populations and may have led to geographic variation in its songs. We investigated the acoustic characteristics of the songs of Yellow Buntings from four populations in central Honshu and found differences among the populations. For example, males at Nagaoka sang short songs with highly frequency-modulated notes, whereas males at Fuji sang long songs with poorly modulated notes. This study demonstrated geographic variation in bird songs on a small scale in mainland Japan. As songs are formed through cultural learning, local songs can arise in loose isolation or for short periods.
Mutualistic interactions between plants and animals can play a critical role in invasion by alien plants. We investigated the expansion patterns of the loquat Eriobotrya japonica in urbanized areas of Tokyo, Japan, and the potential contribution of crows (Corvus spp.) to this process. The loquat produces large fleshy fruits, and preliminary observations suggest that the Jungle Crow C. macrorhynchos is the main vector for loquat seed dispersal in the area. We searched for loquat plants between the 29 stations of the Yamanote Line, a railroad that encircles central Tokyo. We identified the origin of each plant (invasive or planted), and recorded their growth and fruiting patterns. Then, we investigated the relationships between fruit/seed sizes of the plant and the gape sizes of two crow species occurring in the area, along with other possible seed-dispersers (four bird species), to assess their effectiveness as seed dispersers. We confirmed that a considerable number of loquat plants have invaded the area, and that some of them have grown sufficiently large to produce fruits. Both invading and planted loquats were concentrated in the northern parts of the Yamanote Line, and their densities in each section were correlated. Comparison of fruit/seed sizes with avian gape widths suggests that only the two crow species have gapes of sufficient size to be able to consume loquat fruit, and swallow the seeds; thus they are the most likely agents of loquat seed dispersal. We concluded that, although the loquat has a limited range of seed dispersers, crows play a critical role in the invasion and expansion of the species.
Seed dispersal effectiveness (SDE) is one of the best parameters for estimating the benefit that a plant obtains from a dispersal agent. SDE includes quantitative and qualitative components. Previous avian studies of SDE estimation have been conducted mainly in temperate shrub lands or in tropical forests; data are limited for temperate forests, especially, the quality of seed-deposition sites. In this study, we estimated the SDE of birds for Wild Cherry Cerasus jamasakura and Giant Dogwood Cornus controversa fruits in a temperate Japanese forest. These trees prefer sunny sites so we focused on the light conditions at seed-deposition sites and categorized three microhabitat types: forest-gap, forest-edge, and forest-interior. We observed avian seed removal at fruiting trees, conducted a bird census to estimate microhabitat selectivity and collected bird-dispersed seeds. We then counted seedling emergence. Finally, we constructed generalized linear mixed models that combined bird census and dispersed seed data to identify influential seed disperser(s) for each tree species. Frugivorous behavior was recorded for eight avian species for C. jamasakura and 12 for C. controversa. Of these birds, one for the former, and two for the latter preferentially selected forest-gap or forest-edge trees during each fruiting period. The density of dispersed seeds and seedlings was higher in the forest-gap or forest-edge. Additionally, the frequency with which Japanese White-eye Zosterops japonicus visited was a significant variable for seed density in each microhabitat. The results suggested that microhabitat selectivity may affect the density of dispersed seeds in each microhabitat. Furthermore, a bird with a high quantitative SDE may not necessarily also have a high qualitative SDE. Thus, it is important to estimate qualitative and quantitative SDE by focusing especially on the seed-deposition site for each bird in order to evaluate the actual SDE in temperate forests.
An immature Siberian Crane Grus leucogeranus straggled to Niigata, Japan, in late autumn 2016 and remained over winter in an area of rice fields. In this paper the bird's diet and foraging behavior during winter 2016/2017 are described. During daytime, the crane foraged alone, mostly on post-harvest rice fields where it fed almost exclusively on Water Chestnut Eleocharis kuroguwai tubers. Other foods, such as rice grains, earthworms, grasshoppers and fishes, though eaten, were negligible in the bird's diet. The density of water chestnut tubers in the foraging area was estimated to be 3.1±3.0/m2 and the biomass 2.0±2.1 g/m2. The crane's foraging behavior generally included removing any superficial covering material, digging into and removing the soil, exploring the food in the beak and then consuming it with or without rinsing it in groundwater. During foraging, the frequency of food intake varied from 4.8±2.0/10 min to 41.3±9.5/10 min. These results indicate the great significance of water chestnuts in the diet of the Siberian Crane in winter, although further study is necessary for generalization.
This study describes the morphometric variation among Sand Martin Riparia riparia populations in Serbia and assesses the relationship between breeding habitat characteristics and morphometric traits. Univariate and multivariate morphometric analyses based on 11 morphometric characters were performed on 233 adult Sand Martins from five populations. The populations showed differences in five morphometric traits: claw length, bill length, bill width, sternum length, and body weight. The differences were most pronounced in populations breeding at high densities in habitats under least human impact compared with urban habitats. Individuals from the Deliblato Sands Special Nature Reserve differed from all other populations in having distinctive characteristics (lower body weight, longer claws and wider bills). The morphological traits we analyzed are related to nesting, foraging and predator avoidance. Thus observed morphological variation might reflect differences in habitat characteristics.
Loss of mature tropical forests to agricultural expansion often creates landscapes with forest fragments embedded within a matrix of human-modified habitats and land uses. Such habitat fragmentation may be detrimental to species with specialized habitat and foraging requirements and their ability to persist in such landscapes may depend on their adaptability to habitat modification. Great Hornbills Buceros bicornis, among the largest birds in Asian tropical rainforests, depend on large trees for nesting and a diverse array of patchily distributed fruiting trees. In the human-modified landscape of the Anamalai Hills, India, we compared the breeding biology and nesting behaviour of Great Hornbills in contiguous rainforest (N=3 nests) and in modified habitat consisting of coffee plantations and rainforest fragments (N=5 nests). The nesting cycle of seven of the eight nests monitored varied between 114 and 130 days. Nest provisioning behaviour was similar in contiguous forest and modified habitat in terms of visitation and food delivery rates, but visitation tended to be higher and food delivery rate lower during the nestling phase than during incubation. As expected, tree density and native food plant diversity were lower in modified habitat than in continuous forest. The diversity of food provisioned was lower in modified habitat with a 57.5% dietary overlap with contiguous forest. Hornbills in the modified habitat of coffee plantations used non-native tree species for nesting and foraging, indicating their adaptability to modified landscapes.
Climate change-mediated range shifts have been well illustrated for a range of avian species. Here, we report on a new distribution site of the Common Koel Eudynamys scolopaceus in Qinglong Manchu Autonomous County, Hebei Province, China. This site lies about 700 km beyond the previously traditional northern limit of the species' range. Based on publications and birding records of Cuckoos in China, we found that 8 of 17 species had extended their known distribution ranges northward or westward since 1976.
The migratory behavior of Grey Heron Ardea cinerea is poorly known. We tracked an adult Grey Heron with a GPS/GSM transmitter for two consecutive years (2014–2015) including two complete migrations between Dongting Lake, a wintering area, and the Jewish Autonomous Oblast, a breeding area, along with a post-breeding area in Jiamusi City. We found that the Grey Heron migrated without using stopover sites en route and traveled both by day and night. The home-range size and habitat type used varied between life stages (wintering, breeding, and post-breeding periods), but agricultural habitats were used more in winter. Our study revealed for the first time the detail of the year-round movements and habitat use of the Grey Heron.
We examined the diet of young Northern Goshawks Accipiter gentilis before and after fledging through the direct observation of prey items delivered by a single pair breeding in central Tokyo. Observations were conducted from 13 May to 14 August 2015. Three hundred prey items primarily belonging to five bird species and two genera of mammals were recorded both before and after fledging. The species contributing most to the total diet were White-cheeked Starling Spodiopsar cineraceus and Feral Pigeon Columba livia, with pigeons contributing most to total biomass followed by White-cheeked Starling. Prey item composition differed between the periods before and after fledging. After fledging, the contribution of White-cheeked Starling to the diet decreased, whereas that of pigeon increased.
An adult Large-billed Crow Corvus macrorhynchos proved capable of lifting weights of 1,100 g with its bill, equivalent to 1.5 times its body mass. It also attempted various other techniques, using its feet, flapping its wings, and using a fulcrum to flip the weight over. The effort used to lift weights varied greatly and was not always consistent with the weight increase; for example, the crow took more than 12 minutes and 23 attempts to lift 990 g but only took 27 seconds and seven attempts to lift 1,090 g. The crow's strategy seemed to change over a series of experiments, from using muscle power to energy saving techniques.