Variation in plumage color in the family Cuculidae has become an interesting subject for model systems in the study of avian color evolution. It is notable that in certain parasitic species, such as the Common Cuckoo Cuculus canorus and Lesser Cuckoo C. poliocephalus, it is only the females that exhibit color polymorphism, with either gray or rufous morphs. However, a general lack of systematic quantitative data on color morphs means that the underlying mechanism of color morph variation remains unclear. Our studies of wild-captured male and female cuckoos (both of the above species) have shown that their plumage morphs vary not only between the sexes, but also within sexes. In addition, the extent of color variation differs between the two species. Great variations are observed in the plumage morphs of female Lesser Cuckoos from gray to rufous with various kinds of intermediate forms, whereas only the gray females are observed in common cuckoos. Our results show that the range of plumage morphs in cuckoos is much greater than previously thought. Therefore, future studies should first explore the proximate mechanism of plumage maturation, such as the pattern of individual development and the effect of genetic/environmental factors, in order to better understand the adaptive significance of color variation in cuckoos.
Egg colors and patterns have long been of interest for ornithologists and evolutionary biologists, with several hypotheses proposed to explain them. These include: Wallace's hypothesis, the structure hypothesis, the brood parasitism hypothesis and the post-mating sexual selection signal hypothesis. However, none of these are sufficient to elucidate the evolutionary mechanism involved. In this study, egg polymorphism and phylogenetic relationships within the avian family Paradoxornithidae were investigated. When compared with phylogenetic information, we found that egg color matched two size-related clades within the Paradoxornithidae. The larger parrotbills all lay patterned eggs with pale background colors, whereas the smaller parrotbills lay plain pale blue eggs. To our knowledge, this is the first study to detect such a relationship between egg color and pattern and phylogeny in parrotbills, suggesting that they are under strong phylogenetic constraints and can be treated as an important indicator of phylogenetic relationship.
The evolution of egg polymorphism based on strong egg discrimination by hosts of brood parasites may be a specific adaptation against avian brood parasitism. However, different cuckoo-host systems with egg polymorphism may differ in many other aspects during coevolution. We studied the interaction between the Common Cuckoo Cuculus canorus and its host, the Daurian Redstart Phoenicurus auroreus, and detected that cuckoos use an intermediate degree of egg monomorphism to parasitize contrasting dimorphic eggs laid by redstarts. However, redstarts only possess an intermediate ability of egg recognition of dissimilar egg phenotypes with a high degree of recognition error and long latency to rejection. We discuss possible explanations for these observations and suggest that the intermediate degree of egg mimicry in the cuckoo and egg recognition in the redstart may constitute an early stage of disruptive coevolution in egg phenotypes between cuckoos and hosts. Alternatively, intermediate polymorphism may be maintained as a result of an evolutionary equilibrium between hosts and parasites.
Polymorphism provides a classic example of adaptive evolution. A great advantage of studying polymorphism is that the phenotype can serve as a genetic marker; therefore, researchers can take full advantage of this to test a hypothesis based on Darwin's principle of adaptive evolution. Evolutionary theories of polymorphism have been established and suggest that polymorphism is likely maintained through negative frequency-dependent selection. Such selection is mediated by the viewer's perception or recognition of the focal trait as expressed by appearance, such as the colour and pattern of eggs. The viewer's response to that trait selects against the majority of the population, and thus favours the rare type. Such evolutionary dynamics can also be applied to avian brood parasitism, in which parasites exploit the parental care of their hosts. In this review, I describe recent findings in brood parasitic systems, in which polymorphism plays an important role in the coevolutionary arms races, at the egg, chick, and adult stages. Finally, I emphasize the need to synthesize traditional ultimate approaches with proximate approaches, incorporating genomics and psychology, in order to draw a fuller picture of the coevolutionary arms race between avian brood parasites and their hosts.
The Korean peninsula is geographically important for the migration of geese. Several thousand geese visit South Korea every winter, but currently it is unclear which habitats are preferred by the geese. Understanding patterns of habitat usage is important for establishing conservation strategies, as some habitats may be disappearing more rapidly than others making it critical to know whether or not a disappearing habitat is crucial to certain birds. In this study, we investigated the habitat use of the wintering populations of Bean Goose Anser fabalis and Greater White-fronted Goose A. albifrons. We found that the wintering populations of these two geese species in South Korea have stabilized after sudden increases during the mid and late 2000s. Both species formed larger wintering populations at coastal lakes, on reclaimed lands, and at estuaries than on freshwater habitats, which may be related to the availability and/or diversity of food items. Considering that environmental changes resulting from development and climate change are reducing the inshore areas and estuaries, the role of artificial wetlands, such as reclaimed areas that are used as rice fields, is important for conservation of geese that overwinter in Korea.
In most avian species, parents incubate their eggs until they hatch, paying an energetic cost in the process. Incubating individuals are expected to efficiently adjust their investment in incubation according to the thermal demands of their eggs and their partner's contribution to the process. In this study, the effects of ambient temperature, incubation stage, clutch size, and food provisioning by males on the incubation behavior of females, were investigated in the Bull-headed Shrike Lanius bucephalus. We video recorded behavior at 16 nests throughout the 15-day incubation period and established that only females incubate. During the early stage of incubation (5-7 days after completion of the clutch) female shrikes spent more time incubating, with longer periods on the nest (on-bout duration) and shorter periods off the nest (off-bout duration), than during the late stage (9-11 days after clutch completion). Females with larger clutches spent more time incubating than those with smaller clutches. Ambient temperature did not strongly affect female incubation behavior. Male provisioning was positively correlated with the length of time females spent incubating and their on-bout duration. Male provisioning plays an important role in the greater involvement of females in incubation, thereby ensuring normal embryonic development.
Songbirds provide an opportunity to explore the neural mechanism underlying the learning and production of complex sound sequences. Imaging the neural structure at single-cell resolution in large volume tissue helps to disclose the functions of neural circuits involved in the song system. Recent advancements in optical clearing techniques may contribute to successful imaging of large-volume samples of songbird brains. These new clearing methods were originally optimized for rodent nervous tissues and previously have not been tested on avian brains. Here we examined whether SeeDB and ClearT, two of the latest optical clearing methods, are suitable for songbird brains, in addition to rodent brains. These two methods were chosen because of the shortness of time required to complete them and because of their compatibility with common lipophilic dye labeling. We applied these methods to brain sections of Bengalese Finches Lonchura striata var. domestica and laboratory rats Rattus norvegicus, then quantified sample transparency as well as expansion rates. The analyses, using both methods, revealed that finch samples were less transparent than rat brain sections. In samples of both species, ClearT was found to enable higher transparency, but caused more expansion, than SeeDB. It is expected that these clearing methods will be of advantage when investigating the anatomical aspects of the neural basis of birdsong.
We investigated the feeding preferences of the White-cheeked Starling Spodiopsar cineraceus in Korean village groves during the breeding season by means of a fecal dietary analysis using a non-invasive molecular approach. A total of 529 fecal samples were collected from four different study sites, 113 of them (21.4% of all fecal samples) were identified as those of S. cineraceus. Analysis showed that the starling’s diet mostly consisted of animal matter (64.5%), but also contained vegetable matter (32.7%). Terrestrial prey, such as insects and spiders, constituted the largest proportion (65.2%) of species in the diet, although aquatic organisms (26.1%) were also important. Most of the seeds detected in feces were of mulberries, with detection rates rising to 68.1% by the end of May and remaining high until mid-June. Our results suggest that higher water levels in paddy fields due to irrigation could potentially act as an impediment to bird feeding, particularly for small birds such as S. cineraceus and induce a dietary shift to terrestrial organisms from aquatic organisms. In addition, we suggest that human agricultural activities may influence the feeding activities of small bird species such as S. cineraceus in an agricultural ecosystem.
Approximately one-third of all conservation translocations have failed to establish a self-sustaining population. Despite this historically low success rate, reintroduction is increasingly used in species recovery programmes in accordance with IUCN guidelines. Two commonly used methods of reintroduction involve ‘hard’ or ‘soft’ releases. A ‘hard’ release means immediate release from captivity into the wild, whereas ‘soft’ release involves individuals being kept for a period at a pre-release site and/or an extended period under care at the release site. In general, in recent reintroduction programmes, soft release is preferred over hard release because studies have shown that soft release can increase translocation success by encouraging animals to stay near the release point thereby utilizing supplementary food and delaying dispersal. The Crested Ibis Nipponia nippon used to be widespread in Japan, but became extinct in the wild during the early 1980s. In order to re-establish a wild population, a reintroduction programme has been implemented on Sado Island since 2003. Ten ibises were hard-released in 2008, and 20 were soft-released in 2009. In this paper, we quantify the differences in post-release movements by comparing the results of 2008 and 2009 releases, to determine whether release methods influence post-release behaviour. Linear mixed-effects modelling indicates that the post-release movements of birds varied depending on their gender, style of release, and season. In the reintroduction programme for the Crested Ibis on Sado Island, Japan, soft release appears to encourage birds to remain near the release site and to form a flock immediately after release.
Virulence, the amount of harm a parasite inflicts on its host, is integral to elucidating the evolution of obligate avian brood parasitism. However, we lack information regarding how relatedness is linked to changes in behavior and the degree of harm that brood parasites cause to their hosts (i.e., virulence). The kin competition hypothesis combines theory from offspring signaling and parasite virulence models and states that the begging intensity of co-infecting parasites is driven by their relatedness, with concomitant changes in the degree of virulence expressed by parasitic young. We tested this hypothesis using the Brown-headed Cowbird Molothrus ater, an obligate brood parasitic bird whose virulence at the nestling stage is mediated by vigorous begging displays that are used to outcompete host young during feeding bouts. We found support for both predictions of the kin competition hypothesis: first, the begging intensity of cowbirds was greater in a population where cowbirds typically competed against unrelated host nestmates, relative to a population where they often competed against kin. Second, the greater intensity of begging in cowbirds was positively associated with decreased growth in host offspring during the developmental period. Given the dearth of studies on virulence in avian brood parasites, our results notably extend our understanding of how relatedness is linked to parasite behavior and virulence, and they highlight how spatially-isolated host populations can harbor different levels of virulence that are driven by competitive interactions between co-infecting parasites.
Although the relative importance of land use and climate to large-scale bird distributions has received great attention, it is difficult to separate the effects of land use and climate, and there are few studies on bird abundance distributions on a large scale. Here, we examined the effects of land use and climate on the abundance of the nocturnal Jungle Nightjar Caprimulgus indicus in Hokkaido, northern Japan. We chose 125 sampling sites with low correlations (|r|<0.58) between land use and climate, and combined a playback method with a hierarchical model (N-mixture model). We thereby accounted for the possibility that we could not detect all individuals during the field survey. Results show that Jungle Nightjar abundance was greater at sites within a 4−km radius of moderate forest cover (~75%) and with high average temperatures during the breeding season. Moreover, the effects of land-use were greater than those of climate. Mapping predictions of Jungle Nightjar abundance indicated that suitable areas are distributed in southern and central Hokkaido and around the margins of montane zones. Factoring in the covariation of land use and climate, land use may be the most important driver of the distribution of the Jungle Nightjar in Hokkaido.
Parent Procellariiformes alternate between long-range foraging trips to feed in distant productive marine areas and short-range trips to feed in less productive areas around their breeding colony. Foraging trip duration, diet, energy expenditure, and chick growth of Streaked Shearwaters Calonectris leucomelas were compared between two colonies, one on Mikura Island located in the warm and less productive waters of the Kuroshio current, and the other on Sangan Island located in the cold and more productive waters of the Kuroshio/Oyashio transition zone. Parent shearwaters breeding on Mikura alternated between short (≤3 days) trips to Kuroshio waters in order to provision their chicks and long (>3 days) trips to the cold Oyashio region in order to accumulate energy reserves for themselves. Shearwaters breeding on Sangan mainly took short trips (≤2 days) to the nearby Kuroshio/Oyashio transition zone, but also took longer trips (>2 days) to the cold Oyashio region. Parent shearwaters breeding on Mikura, however, made more frequent long trips (24%) than those breeding on Sangan (9%). Parents at both colonies commonly brought Japanese Anchovy Engraulis japonica and Darkedged-wing Flyingfish Cypselurus hiraii for their young, while parents on Mikura also brought Pacific Saury Cololabis saira and stomach oil after long trips. Parents on Mikura delivered energy at a lower rate, resulting in lower chick growth rates and smaller fledging masses than on Sangan. Unlike other Procellariiformes seabirds, shearwater parents on Sangan accumulate their own body reserves even during the chick rearing period because of better foraging efficiency than on Mikura. This may indicate that chicks were satiated by the meals delivered to them allowing parents to utilize the remaining provisions for their own body reserves.
The Sand Martin Riparia riparia is a widely distributed species, but its natural history at high elevation is poorly understood. In this paper, we describe their nesting ecology and their cooperative breeding behavior at an altitude of 3,400 m on the northeast Tibetan plateau. After arriving on their breeding grounds in early May, pairs nested solitarily, excavating nests burrows themselves into vertical stream banks. Burrows averaged 113 cm long. The clutch, averaging 4.9 pure white eggs, was laid during late May and June. Incubation, shared by both parents, lasted 14.7 days, and the young fledged at an average of 23.3 days of age. They were single-brooded and had an overall nest success of 89.5%. Cooperative breeding was observed in two out of 19 nests; in each case a single male attendant assisted the parents. This special social system has not previously been described in this species. More feeding visits were made to the cooperative nests than to non-cooperative nests and the brood size at fledging was larger in cooperative nests. In comparison with lowland populations studied in North America, Tibetan Sand Martins began nesting later, dug longer nest tunnels, produced similar clutch sizes but larger eggs, had a longer nestling period, and achieved higher nest success, suggesting an adaptive pattern to compensate for the stressful conditions at high-elevation.