Many bird species with heterogeneous distribution are at risk of extinction. It is essential to identify and elucidate environmental factors explaining such distribution patterns to develop effective conservation strategies for those species. Yellow Bunting Emberiza sulphurata is an endangered migrant bird species exhibiting heterogeneous breeding distribution in Japan. Here we clarify the spatial distribution and the altitudinal range of the Yellow Bunting breeding range, and detect environmental factors (e.g., climate and topography) influencing their distribution pattern using an extensive dataset from the national breeding birds survey of Japan. The presence of Yellow Bunting during the breeding season (1997–2002) and six environmental factors (temperature, snow depth, elevation, tertiary layer, landslide area and forest edge density) were analyzed using maximum entropy models (MaxEnt). We found that Yellow Buntings were present in a higher proportion of survey grids in northern Honshu (the main island of Japan) than elsewhere in the country, and they mainly occurred in areas below 700 m above sea level. Moreover, the elevation of the occupied grids decreased with latitude. Temperature and snow depth were of greater importance (0.380 and 0.350, respectively) than other factors in explaining the breeding distribution of the Yellow Bunting. Our study highlighted the location of the core areas of the Yellow Bunting's breeding distribution, and demonstrated that lower temperature and deeper snow cover are the critical determinants of those areas. There may be abundant prey and fewer avian competitors, such as resident bird species, in colder regions, and more frequent snow avalanches and water from melting snow may establish the marshy and bushy habitat preferred by Yellow Buntings. These findings are essential for developing effective conservation strategies for the endangered Yellow Bunting. As past mass-trapping may have also influenced the heterogeneous distribution of the Yellow Bunting, this is an important avenue for future research from a different perspective.
An increasing number of reintroduction programs have been set up in recent years in an attempt to reintroduce once extinct species to their indigenous ranges and create self-sustaining populations. However, the released individuals often experience low mating success and fecundity. Appropriate rearing in captivity is considered essential for the successful post-release reproduction of captive-reared individuals. Low post-release mating success and fecundity are also issues in reintroduced Crested Ibis Nipponia nippon populations on Sado Island. These phenomena may be caused by the effects of hand-rearing in captivity, yet temporary hand-rearing is necessary when captive breeding, because rescuing embryos from mortality is essential due to the abnormal behavior of parent birds in captivity. Therefore, the establishment of rearing methods that temporarily protect embryos or chicks while limiting the negative effects of hand-rearing on breeding after release is needed. To overcome these challenges, we tested how captive rearing methods impact post-release courtship behavior, mating success, and fecundity of the ibis. By combining detailed rearing history in captivity with long-term post-release monitoring, we demonstrate that the initiation of parental rearing before the chicks' eyes open is the critical factor leading to increased pseudocopulation frequency and mating success in captive-born male ibis. Based on these results, not hand-rearing the chicks beyond the day after hatching would reduce the impact of hand-rearing on reproduction after release. Rearing methods that take into account the nestling period should be implemented to enhance the efficiency and reduce the cost of avian reintroduction projects.
Little Tern Sternula albifrons sinensis was been categorized as Endangered Class II by the 2020 Ministry of the Environment's Red List in Japan. For an effective conservation program for the taxon, the unit of conservation needs to be understood. In this study, we investigated genetic and morphological diversity as a clue to clarify the units to be protected. Blood samples were collected from 47 individuals in four different breeding sites in Japan (Tokyo, Chiba, Fukuoka, Okinawa). The nucleotide sequences of the control region of mitochondrial DNA were used to analyze their genetic diversity and structure. Basic morphological features were also compared. Nucleic acid base substitution, deletion, or insertion were identified at 30 sites of the 1029-bp sequence alignment of the control region, leading to identification of 30 different haplotypes. Genetic diversity was high in the four breeding populations, and haplotype frequencies showed no indication that specific genotypes were present at extreme frequencies. This suggests that the population of Little Tern nesting in Japan has been maintained without recent bottleneck events. The haplotype network formed two major haplotype groups from the 30 haplotypes. Haplotypes of one group were abundant in the Tokyo, Chiba, and Fukuoka populations. In contrast, those of the other group were frequent in the Okinawa population. Pairwise haplotype analysis between populations also revealed that the genetic variations at Okinawa differ from those of the remaining three populations. Furthermore, the Okinawa population showed different morphological characteristics compared to the Tokyo/Chiba populations. These results collectively suggest that the population of Little Terns in Japan is divided into at least two different populations.
In heterogeneous landscapes, birds may mistime their breeding attempts relative to local food abundance. How birds cope with this challenge has been little studied. In this study, we compared the provisioning behavior and nestling condition of the Green-backed Tit Parus monticolus nesting in a landscape mosaic comprised of native mixed-oak forests and exotic Japanese Cedar Cryptomeria japonica plantations. Parent birds in the larvae-poor plantations time their breeding as they do in the larvae-rich forests and have clutches of similar size. We found that parent birds were flexible in adjusting their criteria for prey choice on the basis of larval abundance. In early spring, in cedar plantations where larval abundance was low, male parents maintained constant nearby feeding trips to the early broods, just as they did in the mixed-oak forests, but reduced their dietary specialization on larvae, while female birds increased their provisioning frequency. Combining both parents' efforts, the early brood nestlings raised in the cedar plantations received food deliveries more frequently and with a higher proportion of non-larval prey than their counterparts did in the mixed-oak forests. In contrast, during late brood rearing, when larvae were abundant, both parents in the plantations foraged heavily on larvae at the expense of other prey, just as they did in the mixed-oak forests. We found that parent birds reared heavier nestlings as the contribution of large larvae to the diet increased. Moreover, the nestlings during early broods in the plantations had lower body weights than their counterparts in the mixed-oak forests. We suggest that the provisioning flexibility of Green-backed Tits helps them gather food for raising nestlings when their breeding attempts are less synchronized with the larval food supply in their habitat. As a result, they can breed successfully in the exotic cedar plantations.
Animals emit vocalizations related to internal or external states, such as hormone levels or predation risks. The Java Sparrow Lonchura oryzivora, a songbird, produces similar trill-structured calls in both aggressive and affiliative situations. A previous study found that trills produced in aggressive situations (AG trills) are faster, louder, and have a wider range of frequencies than trills produced in affiliative situations (AF trills). To assess whether Java Sparrows perceive these trills as different calls, we conducted a playback experiment using a habituation-dishabituation paradigm. In this paradigm, we first played a stimulus set for ten minutes (habituation stimulus), and after that we played either a test stimulus set or a control stimulus set. We analyzed behavioral changes in the study bird that took place between the last minute of the habituation stimulus and the next stimulus set (test or control). As trill stimuli, we used natural AG and AF trills (Experiment 1) and trills in which the trill rates and syllables types were modified (Experiment 2). The results showed that Java Sparrows distinguish between AG and AF trills (Experiment 1). However, when the trill acoustic structure was modified, they distinguished between the different syllable types, but not between different trill rates. As we used a natural behavior as an index, we could not measure the perceptual limit of trill discrimination in these birds. Instead, here, we asked whether the difference between AG and AF trills is meaningful or not, and which acoustic features were important for discrimination. To fully understand how birds perceive vocalizations in the context of communication, more experiments are required, both controlled experiments utilizing operant conditioning and electrophysiology, and multimodal experiments that reflect natural social relationships.
Egg pattern plays a critical role in avian brood parasitism where a brood parasite exploits a host's parental care by laying eggs in host nests relying on the host to rear the parasitic egg(s). It has been demonstrated that many hosts have evolved an ability to recognize and reject parasitic eggs, based on differences in egg patterns, as a defense against brood parasitism, while some parasites have evolved egg mimicry to counter the host defense. Egg pattern is a complex phenotype and its quantitative evaluation has been a focus of much research. In this paper, we propose a novel method for quantifying an egg pattern and assessing the degree of egg pattern mimicry—a measure of the similarity of a parasite egg to host eggs. Our approach is based on image analysis focused on local binary pattern (LBP) and its variant completed local binary pattern (CLBP) that captures the local structure of a pattern in an image. We compare the results obtained by LBP and CLBP with human-eye evaluation, a classical method widely used in previous studies. Both LBP and CLBP can successfully assess the similarity in egg pattern that is positively correlated with human-eye scores with a high accuracy rate. LBP tends to perform better than CLBP at small scales while CLBP performs better for a wide range of larger scales. Our method can be an effective alternative means of assessing the degree of egg pattern mimicry objectively, providing a useful tool for biologists studying avian brood parasitism. Many bird species have specific eggshell patterns (e.g. spots, blotches, lines) and it has been suggested that these patterns are an important functional trait, such as for camouflage against predators. We propose our method as a useful and objective tool for assessing egg patterns.
The Indian coast and its adjacent wetlands host large congregations of shorebirds, including winter and passage migrants of high conservation priority, along the Central Asian Flyway. Identifying crucial wintering and stopover sites and seasons is an important step toward conserving shorebirds and their habitats along the Indian coast. We assessed spatial and temporal patterns of shorebird composition from January 2015 to December 2016 at seven estuaries along Maharashtra's Sindhudurg district, which is located on India's west coast, a coastal zone of international importance for shorebirds. Three potential shorebird habitats –mangroves, mudflats, and sandy beaches – were selected at each of the estuaries chosen for the study. We established three vantage points, one each in the mangrove, mudflat, and sandy beach areas, to count birds during low tide. The total count method was followed to count birds, and occasional photograph-based counts were also made when flock size was big or the flocks kept changing. We recorded 31 species of migratory shorebirds, of which 68% wintered and 32% used the Sindhudurg coast as migratory stopover site. We found significantly high richness and abundance of shorebirds during winter and in the mudflats. nMDS was used to determine species composition of shorebird across habitats and months and revealed distinct patterns of composition in five unique phases: arrival, wintering, early departure, departure, and breeding. Our results revealed that the species composition of shorebirds is not homogenous across sites and months, and is largely driven by the habitat heterogeneity of estuaries, seasonality, and anthropogenic disturbances. These results provide baseline information on shorebirds along a stretch of India's west coast and highlight the importance of mudflats and non-protected coastal wetlands for shorebirds.
Rural areas provide various habitats for birds, and some studies have revealed habitat associations in rural bird communities in Japan. Previous studies have primarily focused on waterbirds or the habitat values of abandoned farmland, thus little is known about the importance of cultivated land for rural bird communities. Therefore, in this study, I clarified the characteristics of the avifauna in a rural area of the Ishikari Plain in Shinshinotsu Village, Western Hokkaido, and examined habitat utilization of cultivated land by eight major grassland species; Bull-headed Shrike Lanius bucephalus, Eurasian Skylark Alauda arvensis, Black-browed Reed Warbler Acrocephalus bistrigiceps, Siberian Rubythroat Calliope calliope, Stejneger's Stonechat Saxicola stejnegeri, Chestnut-eared Bunting Emberiza fucata, Black-faced Bunting E. spodocephala, and Common Reed Bunting E. schoeniclus. I conducted bird surveys along three 2-km line-transect routes among rice fields with some wheat, non-wheat crop fields, and weedy areas from April to October from 2016 to 2018. I recorded a total of 51 species of three general types: grassland birds, residential birds, and water birds. Rice fields in this study areas were flooded during early to mid-May to mid to late August, however species-specific habitat utilization analyses revealed that a small number of Eurasian Skylark, Stejneger's Stonechat, and Chestnut-eared Bunting inhabited the rice fields during study periods other than the flooding season. A relatively large number of Eurasian Skylark was observed in wheat fields and non-wheat crop fields throughout the study period, and Stejneger's Stonechat and Chestnut-eared Bunting were temporarily observed in those habitats. The other five species only rarely observed in rice, wheat, or non-wheat crop fields, but all eight species were observed in weedy areas. The characteristics of the avifauna in this rural area of Western Hokkaido proved to be quite different from previous studies conducted in the Kanto Region of Honshu. For the conservation of biodiversity and birds in rural areas, it is necessary to investigate the avifaunal characteristics of various regions of Japan.
The Daurian Redstart Phoenicurus auroreus has expanded its breeding distribution in recent years and now breeds in Japan, previously only part of its wintering range. We analyzed the breeding habitat selection of the population at the nest and territory scale in the Kirigamine Highlands, Nagano, Central Japan. At the nesting scale, the birds chose buildings frequently occupied by humans, while at the territory scale, they avoided sites in larger built-up areas. Our findings demonstrate that the breeding habitat selection of Daurian Redstart is influenced by environmental factors at both nest and territory scales.
Avian dispersal patterns vary among populations and breeding conditions, although female passerine birds tend to disperse longer distances from natal sites than do males. Experimentally, we manipulated the breeding density of the Eurasian Tree Sparrow Passer montanus by establishing high and low nest-box density plots. We banded nestlings and recaptured them one year later. Females were more often found at non-natal sites than were males, and both males and females from high density plots dispersed shorter distances than those from low density plots.
Ural Owls Strix uralensis often use nest boxes, but there have been few reports of them using other man-made structures. We discovered a Ural Owl nest on a steel tower in a suburban area in Ibaraki Prefecture, central Japan, in May 2019. The nest had been built in a jointed part of the steel frame that supported the body of the tower, which was approximately 10 m-high. In this case, a neighboring shelterbelt seemed to provide the owls with leaf litter for the nest floor and hiding places for the parents and their fledglings.
Fundamental demographic data of insular populations of Otus owls are not available for most species. This study investigated the population size and the sex ratio of the Ryukyu Scops Owls Otus elegans on Hateruma Island. Capture-recapture data was obtained by intensive marking and route census surveys from July to September in 2021. Analysing the data using a site-occupancy model combined with a data-augmentation technique, the population size was estimated as 155.470 individuals (97.575 males and 57.895 females), with a significant male-biased sex ratio (0.631).
This study aimed to identify whether Siberian Crane Leucogeranus leucogeranus regularly fly after sunset, and what determines a cranes' decision to continue its migration in darkness. Based on observations in East Siberia (2012–2021), 4–69% of cranes passed over observation points during the night, regardless of the presence of positive environmental factors suitable for cranes, such as wetland-rich areas, and continued in the dark towards areas with inappropriate habitat for their landing. This suggests that their decision to continue migrating after nightfall is induced by internal factors and contributes insights into the phenomenon of nocturnal crane migrations.