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Stopover sites are critical for refueling and resting by migrating birds. Clarifying the habitat requirements of migratory birds during stopover is important for understanding migration ecology and for conservation management. Habitat use by migratory birds at stopover sites, however, has been inadequately studied, and individual variation in habitat use among species is largely unexplored. We tracked the movement of migrating Whimbrels, Numenius phaeopus, using Global Positioning System–Global System for Mobile Communication tags at Chongming Dongtan, an important stopover site in the South Yellow Sea, China, in spring 2016 and in spring and autumn 2017. Multinomial logistic regression and multimodel inference were used to detect the effects of the individual bird, the diel factor (day vs. night), and tide height on the habitat use by Whimbrels during the stopover. The activity intensity of Whimbrels was lower during the night than during the day, while the maximum distance that tagged Whimbrels moved was similar between day and night. The saltmarsh and mudflat were intensively used by all of the individuals in all three seasons: > 50% and 20% of all records were obtained from the saltmarsh and mudflat, respectively. Habitat use significantly differed among individuals; the farmland and woodland were used by some individuals in spring 2016, while the restoration wetland near the intertidal area was used by some individuals in 2017. In general, the saltmarsh, farmland, and woodland were more frequently used in the daytime, while the mudflat was more frequently used at night. As tide height increased, the use of the mudflat decreased while the use of the saltmarsh increased. The results suggest that individual-based bio-tracking can provide detailed data on habitat use both during the day and at night. Differences in habitat use among individuals and periods highlight the importance of diverse habitats for bird conservation.

Sex ratio is a fundamental concept in evolutional biology, and theory predicts that parents should invest in sons and daughters according to the fitness returns they expect from them. The fitness returns may depend on the timing of breeding and on parental conditions leading to sex ratios that depend on breeding date and/or parental quality. Here, we investigate the offspring sex ratio in a small shorebird, the Kentish Plover Charadrius alexandrinus, in a large breeding population in Eastern China, and test whether the parents adjust their offspring’s sex in response to hatch date, brood age and their own body condition. Using 1264 chicks from 676 broods that were molecularly sexed, we show that hatchling sex ratio was not significantly different from unity. Hatchling sex ratios were not related to hatch date or to the body condition of parents. In addition, we sexed 138 eggs that were confiscated from illegal egg collectors and found that the mortality of female and male embryos was not significantly different. The latter result is important by suggesting that neither primary sex ratio (i.e., at conception) nor secondary sex ratio (i.e., at hatching) is biased. Taken together, the even offspring sex ratio in Chinese Kentish Plovers is consistent with recent analyses of six plover populations that found even sex ratios at hatching. Future works should investigate whether the even sex ratio persists into adulthood, or it may shift toward more males (or females) due to sex-biased mortalities of juveniles and/or adults.

Parents are expected to make fine-tuned decisions by weighing the benefits of providing care to increase offspring survival against that of deserting to pursue future mating opportunities. A higher incentive for the rarer sex in the population indicates an impact of mating opportunities on parental care decisions. However, in a dynamic breeding system, deserting the offspring and searching for a new mate would influence mating opportunities for both sexes. Sex-specific costs and benefits are expected to influence males’ and females’ parenting strategies in different ways. Here, we investigated Chinese penduline tits, Remiz consobrinus, which exhibit flexible parental care strategies: uniparental care by the male or female, biparental care, and biparental desertion occur in the same population. We show that male penduline tits change their parental behavior over the breeding season; they desert clutches produced early in the season but care for the late season clutches. The change in male parenting behavior is consistent with the seasonal decline in mating opportunities. In contrast, parenting by females did not change over the breeding season, nor was it associated with seasonal variation in mate availability. Taken together, mating opportunities have different associations with parental behavior of male and female Chinese penduline tits. We recommend an inclusion of mating opportunities for both sexes simultaneously in order to understand one of the fundamental decisions in parental care evolution—care or desert. Significance statement: Divorce is a common feature of both human and nonhuman animal societies. Theoretical studies suggest that one of the drivers of divorce is enhanced mating opportunity, i.e., parents with higher mating opportunities are more likely to abandon their family than those with low mating opportunities. Here, we investigate the dynamics of parental behavior and mating opportunities in a wild population of a small songbird, the Chinese penduline tit Remiz consobrinus. This species exhibits one of the most diverse avian breeding systems wherein both uniparental (male or female) and biparental rearing can be seen in a single population. We show that male penduline tits abandon their offspring in response to enhanced mating opportunities while the female parental behavior remains unaffected. This implies the relationship between mating opportunities and parental care is more complex than currently acknowledged and requires further investigation.

Birdstrikes are an important threat to aviation safety. A standardized, scientific process for assessing birdstrike risk could prevent accidents, thereby improving the flight safety and reducing economic losses. However, China currently lacks a unified birdstrike risk assessment system. Here, we propose and validate a new model for assessing birdstrike risk in order to fill that need. The model consists of two elements. First, empirical data are collected on the occurrence of birds at the airport and in a surrounding 8 km buffer. Second, each species is evaluated with a risk assessment matrix that takes into account the number of birds, weight, flight altitude, a tendency to cluster, and range of activity. These five factors allow each species to be divided into one of three risk levels: high danger (level 3), moderate danger (level 2) and low danger (level 1). We propose corresponding birdstrike prevention measures for each level. We apply this method to the civil aviation airport in Ordos, China. We found that 20 of the 118 species of birds in and around the airport were high danger birds (level 3). To validate this process, we compared these species with records of birdstrike accidents in a database maintained by the Civil Aviation Administration of China (CAAC) for 2007–2016. We found that 42% of the species we identified as high risk had been involved in at least one birdstrike accident, and that the remaining 58% belonged to families that appeared in the database. The high degree of overlap gives us high confidence in the practicality of our risk assessment model, which is based on the risk management concept of ISO 31000. Critically, this new model and method for predicting bird strike risk can be replicated at other airports around the world, even where no extensive records have been kept of past birdstrikes.

The Chinese Penduline Tit (Remiz consobrinus) is a small passerine that breeds in Northeast Asia. Despite its common appearance and its high encounter rate, the breeding biology of this species has remained largely unknown. In this paper, we describe for the first time the breeding biology and parental care system of the Chinese Penduline Tit in the coastal area of Northeast China. As a migratory species of birds, it arrives at the Liaohe Delta in late April, the males establish territories in early May, and breeding pairs build their nests from May to July. Most nest building occurs from mid-May to early June. The females produce small white eggs (egg mass, 1.0 ± 0.1 g) and a clutch size of 6.8 ± 0.6 eggs. The parental care system is complicated in Chinese Penduline Tits: uniparental care is dominant (80%) in this population, with a majority (71%) of female-only care and 9% male care for all brooding nests, together with 4% biparental care and 16% biparental desertion. Chicks hatch after 13.9 ± 1.0 days of incubation and fledge after 22.1 ± 1.0 days. The hatching success and nestling survival are 86.7 and 80.6%, respectively. Furthermore, breeding failure is 23.4%, which is commonly caused by predation and nests blown away by strong winds. Compared to other species of the Remiz genus, the Chinese Penduline Tit shows much similarity to the Eurasian Penduline Tit (Remiz pendulinus) but large differences compared to the White-crowned Penduline Tit (Remiz coronatus) with respect to breeding habitat, breeding density, nest site selection and parental care system. Moreover, the good nest attributes, relatively high nestling survival and low risk of nest failure may contribute to the prevalence of the uniparental care system in this Chinese Penduline Tit population.

Incubation is an energetically demanding phase of avian reproduction. Single-sex incubators are often faced with a direct conflict between incubation and foraging. We report an unusual incubation behavior of the Sichuan Partridge (Arborophila rufipectus), with long recesses of females and embryonic hypothermia, at Laojunshan National Nature Reserve, southwest China. The Sichuan Partridge is a globally endangered species that inhabits subtropical evergreen and deciduous broadleaf forests at 1100–2250 m a.s.l. Female Sichuan Partridges incubated eggs alone, and typically took one long incubation recess of 4.5 ± 1.2 h (mean ± SD) day−1. They left the nests at 7:36 a.m. (±50 min) and returned at 12:06 p.m. (±70 min). Nest attentiveness was 81.2 ± 5.2% of the entire incubation period. Females prolonged the recess duration and decreased nest attentiveness significantly in response to high disturbance risk and bad weather. Although eggs experienced ~4.2 h below 26 °C (the physiological zero temperature) for each recess, the total hatching rate was 88.4%, suggesting that embryonic hypothermia had minimal negative effect on the hatching rate. For Sichuan Partridge, the ability to withstand embryonic hypothermia may be an adaptation to cold montane environments.

Background Speciation with gene flow is an alternative to the nascence of new taxa in strict allopatric separation. Indeed, many taxa have parapatric distributions at present. It is often unclear if these are secondary contacts, e.g. caused by past glaciation cycles or the manifestation of speciation with gene flow, which hampers our understanding of how different forces drive diversification. Here we studied genetic, phenotypic and ecological aspects of divergence in a pair of incipient shorebird species, the Kentish (Charadrius alexandrinus) and the White-faced Plovers (C. dealbatus), shorebirds with parapatric breeding ranges along the Chinese coast. We assessed divergence based on molecular markers with different modes of inheritance and quantified phenotypic and ecological divergence in aspects of morphometric, dietary and climatic niches. Results Our integrative analyses revealed small to moderate levels of genetic and phenotypic distinctiveness with symmetric gene flow across the contact area at the Chinese coast. The two species diverged approximately half a million years ago in dynamic isolation with secondary contact occurring due to cycling sea level changes between the Eastern and Southern China Sea in the mid-late Pleistocene. We found evidence of character displacement and ecological niche differentiation between the two species, invoking the role of selection in facilitating divergence despite gene flow. Conclusion These findings imply that ecology can indeed counter gene flow through divergent selection and thus contributes to incipient speciation in these plovers. Furthermore, our study highlights the importance of using integrative datasets to reveal the evolutionary history and assist the inference of mechanisms of speciation. Electronic supplementary material The online version of this article (10.1186/s12862-019-1449-5) contains supplementary material, which is available to authorized users.

Flight loss in birds is as characteristic of the class Aves as flight itself. Although morphological and physiological differences are recognized in flight-degenerate bird species, their contributions to recurrent flight degeneration events across modern birds and underlying genetic mechanisms remain unclear. Here, in an analysis of 295 million nucleotides from 48 bird genomes, we identify two convergent sites causing amino acid changes in ATGLSer321Gly and ACOT7Ala197Val in flight-degenerate birds, which to our knowledge have not previously been implicated in loss of flight. Functional assays suggest that Ser321Gly reduces lipid hydrolytic ability of ATGL, and Ala197Val enhances acyl-CoA hydrolytic activity of ACOT7. Modeling simulations suggest a switch of main energy sources from lipids to carbohydrates in flight-degenerate birds. Our results thus suggest that physiological convergence plays an important role in flight degeneration, and anatomical convergence often invoked may not., Flight loss has occurred numerous times in bird evolution. Here, the authors examine convergent sites in the exonic and intronic sequences of 48 bird genomes, finding amino-acid changes in two genes, ATGL and ACOT7, with potential implications for a change in metabolism rather than anatomy.

Sex allocation theory predicts that parents should adjust their investment between female and male offspring when the fitness return of producing them differs. Genome-wide heterozygosity is related to many aspects of individual fitness, and an individual’s heterozygosity is usually determined by the genetic characteristics of its parents. When heterozygosity affects fitness differently for female and male offspring, parents may be expected to manipulate offspring sex ratio based on their own genetic characteristics. We examined whether parental genetic characteristics affected primary offspring sex ratios in a small passerine bird, the black-throated tit (Aegithalos concinnus). We found that offspring heterozygosity was significantly related to the heterozygosity of parents and the relatedness between parents. Importantly, genetic heterozygosity had a significantly negative effect on the survival of male but not female black-throated tits, implying higher variance in fitness in males than in females regarding the genetic heterozygosity inherited from parents. This sex-specific effect of heterozygosity on fitness provides black-throated tit parents with a potential reason to adjust offspring sex ratio in relation to their own genetic characteristics. However, although we found a seasonal decline of offspring sex ratio (proportion of males), offspring sex ratio was associated with neither the relatedness between parents nor the heterozygosity of parents. The results suggest that at least based on current data, there is a lack of evidence that black-throated tit parents manipulate offspring sex ratio with respect to their own genetic characteristics. The correlation between genome-wide heterozygosity and individual fitness has been extensively studied, but its potential role in mediating parental manipulation of offspring sex ratio has received attention only recently. If heterozygosity affects fitness differently for the two sexes of offspring, parents are likely to adjust their investment between female and male offspring based on their own genetic characteristics. This is because their own genetic characteristics determine their offspring’s heterozygosity and therefore fitness returns to parents. Existing studies have provided support to this hypothesized manipulation of offspring ratio, but studies in the area remain scarce. Our study shows that parents of a bird species do not manipulate offspring sex ratio with respect to their own genetic characteristics, even when there is a sex-specific heterozygosity-fitness correlation.

Choice of mating partners may affect fitness. Both phenotypic and genetic traits have been shown to play roles in the mating processes of animals. We investigated the roles of phenotypic and genetic characteristics in the patterns of social mating in the Silver-throated Tit (Aegithalos glaucogularis), a sexually monochromatic species that exhibits sexual size dimorphism, rarely sings, does not occupy territories, and has a relative low level of extrapair paternity. To explore the role of phenotype traits, we tested for assortative mating based on the sizes of seven morphological traits. To explore the role of genetic traits, we tested for assortative mating with respect to genetic heterozygosity (the heterozygous mate hypothesis) and whether birds mated with genetically dissimilar individuals (the compatible mate hypothesis). We found significant correlations between paired individuals for bill length and body length, indicating possible assortative mating based on these two traits. In contrast, genetic heterozygosity was not correlated between paired individuals, and the mean relatedness of the mates was not significantly different from that of randomly mated individuals, which do not support the idea that Silver-throated Tits assortatively mate with heterozygous individuals or choose genetically dissimilar mates. Also, individual heterozygosity was not reflected in the measured morphological traits, as no correlation was detected. Neither the individual heterozygosity nor the relatedness between mates was correlated with reproductive performance measures, including clutch size, brood size, and number of fledglings. However, we found that clutch size increased with female body length, which could explain the benefit to males of mating with larger females. Taken together, while our current data failed to provide evidence for an effect of genetic characteristics on the social mating pattern of Silver-throated Tits, the results suggest that phenotypic traits are likely associated with their mating pattern.

The explanation for extra-pair paternity (EPP) variation continues to attract research interest in the area of avian breeding systems. Comparisons among closely related species are recommended to explore factors that affect EPP rate variations. We utilised microsatellite markers to investigate extra-pair paternity in two sympatric populations of congeneric Black-throated Tits, Aegithalos concinnus, and Silver-throated Tits, A. glaucogularis. The two species share a similar breeding period at our study site and have helpers during breeding at some nests. The results suggest that the two species had low levels of extra-pair paternity: 5.7 % of the offspring in the Black-throated Tits and 6.8 % of the offspring in the Silver-throated Tits. The proportion of broods with extra-pair paternity in the Silver-throated Tits (33.3 %) was higher overall than the Black-throated Tits (17.2 %). This difference is consistent with the prediction by their different male attendance of incubation, but failed to be explained by major ecological factors. On the one hand, we conducted the study at the same site during the same time, which therefore limited the potential effect of different environmental conditions and habitat on their EPP incidence. On the other hand, other factors such as the inter-nest distances failed to explain the observed pattern. Current results also could not rule out an effect of evolutionary history on the EPP patterns of these two related species. Our research on their cooperative breeding system found a low proportion of cooperative breeding nests with offspring sired by helpers (Black-throated Tit, 8.3 % and Silver-throated Tit, 25.0 %), indicating that a direct reproductive benefit is not a likely major reason for the existence of the helpers in these two species.

Knowledge of the historical responses of animal species to climate changes is critical for understanding their evolutionary history and conservation. During the late Quaternary period, Southeast Asia had a larger land area than today due to lower sea levels, and its terrestrial landscape was covered by extensive forests and savannah. To date, however, the general fluctuations in landscape distribution and their impacts on the demographics history of native species during the late Quaternary periods are still disputed. Specifically, the responses of animals on Hainan Island, which is located in the northernmost region of Southeast Asia, to historical climate changes, are poorly understood. Here, we performed a series of demographic analyses based on mitochondrial DNA genes to examine the response of the resident Hainan Peacock Pheasant (Polyplectron katsumatae) to climate change. Unlike the pattern of population collapse during the ice age and expansion during the warming period, we detected a historical expansion pattern in the demographic history of Hainan Peacock Pheasant through the late Quaternary period. It was concluded that the Hainan Peacock Pheasant survived through the late Quaternary periods, despite of its currently limited distribution and population size on Hainan Island. Anthropogenic influences must be considered in conservation planning due to their impacts on currently fragmented habitats and populations. phylogeography, Quaternary, Hainan Island, Polyplectron katsumatae, conservation

Although knowledge of breeding biology is fundamental for investigating the variation and evolution of avian reproductive strategies, research on Asian Aegithalos tits remains limited. The breeding biology of sympatric populations of Black-throated Bushtits (Aegithalos concinnus) and Silver-throated Bushtits (A. glaucogularis) was studied in the Dongzhai National Nature Reserve in central China from 2007 to 2010. Both species produced one brood annually. Clutch sizes, brood sizes and nesting success were not different between species. Parents of both species participated in all breeding activities, except for the male Silver-throated Bushtits, which were not involved in incubation. Cooperative breeding behaviours were observed in the studied populations of both species. Most helpers were found at the provisioning stage, during which time 1–2 helpers were present at 20% of Black-throated Bushtit nests (n = 50) and 30% of Silver-throated Bushtit nests (n = 40). All marked and confirmed helpers of both species were males. Compared with other Aegithalos species and populations, differences in either the occurrence of helpers or the proportion of nests with helpers indicate that the breeding strategies may vary with species and populations, and therefore, more efforts focusing on their basic biology and ecology are required.

Dispersal, defined as a linear spreading movement of individuals away from others of the population is a fundamental characteristic of organisms in nature. Dispersal is a central concept in ecological, behavioral and evolutionary studies, driven by different forces such as avoidance of inbreeding depression, density-dependent competition and the need to change breeding locations. By effective dispersal, organisms can enlarge their geographic range and adjust the dynamic, sex ratio and genetic compositions of a population. Birds are one of the groups that are studied intensively by human beings. Due to their diurnal habits, diverse life history strategies and complex movement, birds are also ideal models for the study of dispersal behaviors. Certain topics of avian dispersal including sex-biased, asymmetric dispersal caused by differences in body conditions, dispersal processes, habitat selection and long distance dispersal are discussed here. Bird-ringing or marking, radio-telemetry and genetic markers are useful tools widely applied in dispersal studies. There are three major challenges regarding theoretical study and methodology research of dispersal: (1) improvement in research methodology is needed, (2) more in-depth theoretical research is necessary, and (3) application of theoretical research into the conservation efforts for threatened birds and the management of their habitats should be carried out immediately.

The Tibetan Eared-pheasant Crossoptilon harmani is a rare species native to China. A captive population has been established in the Beijing Zoo since 1999. In order to determine the kinship of the offsprings in 2001, randomly amplified polymorphic DNA (RAPD) was used to examine the parenthood of seven Tibetan Eared-pheasants in the Beijing Zoo. To amplify the genomic DNA of each individual, 53 arbitrary primers were selected. The results of amplifications showed that 14 primers had clear and distinct RAPD patterns. Totally, 226 amplified fragments were generated by RAPD in this study. Cluster analysis of the seven Tibetan Eared-pheasants indicated that all the four young birds had the same father (No.5 male). This study provides a practical method to determine the relationship of offsprings whose parents are unknown in birds.

Home range and habitat use of male Reeves’s pheasant (Syrmaticus reevesii) were studied during winter of 2001∼2002 and 2002∼2003 in the Dongzhai National Nature Reserve, Henan Province. Results from five individuals of Reeves’s pheasant with over 30 relocations, indicated that the average size of home range was 10.03 ± 1.17 hm2 by Minimum Convex Polygon method, 8.60 ± 0.35 hm2 by 90% Harmonic Mean Transformation method, and 9.50 ± 1.90 hm2 by 95% Fixed Kernel method. It was observed that the winter range is smaller than that in the breeding season. The mean core area of the home range was found to be 1.88 ± 0.37 hm2. Although the habitat composition of the core area varied greatly for individuals, a large part of the habitats used were composed of confier and broadleaf mixed forests, masson pine forests, fir forests, and shrubs. Habitat use within the study area was non-random, while habitats within home ranges were randomly used. Habitat use was dictated by tree diameter at breast height, shrub height and coverage at 2.0 m. The proximity between forests and shrubs were also found to be important in providing refuge for the birds during winter. Recommendations for conservation management include protecting the existing habitats in Dongzhai National Nature Reserve, increasing suitable habitat for Reeves’s Pheasant through artificial plantations (e.g. firs), and restoring some parts of the large shrub area into forests.

Cross-species microsatellite amplification is an effective way of obtaining microsatellite loci for closely related taxa in bird species. The Reeves's pheasant, Syrmaticus reevesii, is a vulnerable species endemic to China. To improve population genetics and parentage analysis studies in this species, we obtained nine polymorphic microsatellite markers, in addition to the nine markers previously isolated, from the cross-species amplification of 52 markers. The number of alleles per locus varied between two and 12 with expected heterozygosity ranging from 0.298 to 0.714 (n = 107). The success rates of simulated paternity tests using CERVUS software improved at different confidence levels after adding these markers to the previous ones.