Red-crowned Crane Grus Japonensis Research Articles

Integrated Assessment of Survival, Movement, and Reproduction in Migratory Birds: A Study on Evaluating Reinforcement Success.

Conservation managers increasingly employ reinforcement techniques to bolster declining populations by reintroducing non-wild individuals born in captivity into natural habitats, but success rates remain modest. In this study, the success is evaluated of reinforcement efforts using satellite tracking and field observation data collected between 2010 and 2021. It focuses on 13 non-wild individuals, as follows: seven red-crowned cranes Grus japonensis, two white-naped cranes Antigone vipio, and four demoiselle cranes Anthropoides virgo, as well as five wild individuals including two red-crowned cranes and three white-naped cranes. The assessment criteria included survival, movement, and reproduction, utilizing a comprehensive scoring method. The scoring process indicates that more timely field observation records and the movement pattern scoring combining models and trajectories can improve the accuracy of estimation. From the results, although wild individuals generally achieve higher scores across these metrics, statistical differences were not significant possibly due to limited sample size. Notably, non-wild individuals frequently displayed residence, nomadic, or abnormal migration. In addition, field observations underscored the benefits of pairing non-wild individuals with their wild counterparts to enhance migration success. So in order to enhance migration success, it is advisable to release non-wild individuals approaching sexual maturity in proximity to wild subadult flocks during the breeding or summering periods. Additionally, during the overwintering phase, these individuals should be released in areas where wild populations are concentrated.

Breeding records and the detection of nesting predators of wild-release red-crowned cranes into non-breeding areas of the Yancheng National Nature Reserve, China.

The western population of the red-crowned crane Grus japonensis in mainland China has been decreasing in the past few decades and wild population enhancement programmes have been launched in this country. First, 14 captive-bred red-crowned cranes were released into the core area of Yancheng National Nature Reserve for Rare Birds (YNNR), one of the most important wintering areas of this species, in 2013 (seven individuals) and 2015 (seven individuals) and then 8 more captive-bred cranes were released into YNNR from February 2022 to February 2023. We used satellite positioning and drone monitoring to study the status of released cranes. The results showed that two individuals (No. BJZ001 and BJZ008) from the first group of released cranes were found breeding in 6 of 7 years in the YNNR from 2017 to 2023. Three individuals (No. WNNR022, WNNR025 and WNNR026) from the second group of released cranes were recorded breeding in YNNR in 2023. All released cranes lived in the YNNR year round and did not migrate with wild cranes. Raccoon dogs, Nyctereutes procyonoides, were first recorded as red-crowned crane nest predators in the YNNR. Although these released cranes breed successfully in the YNNR, nestlings might face the threat of predators in non-traditional breeding areas. Further research is needed to determine whether offsprings of released individuals migrate with wild cranes and if breeding in their original wintering grounds is truly beneficial for population growth.

Analysis of Crop Consumption Using Scatological Samples from the Red-Crowned Crane Grus japonensis in Eastern Hokkaido, Japan.

Total DNA extracts from the intestinal contents of 60 flying red-crowned cranes (juveniles, subadults and adults) found dead in 2006-2021, and the feces of 25 chicks collected in June and July of 2016-2018, were used for PCR reactions with primers specific for 16 crops, followed by high-throughput sequencing. The most predominant crop detected was corn in adult and subadult cranes (61.7%). Other grains (barley, wheat, soybean) (5.0-8.3%) and vegetables (tomatoes, Chinese cabbage, etc.) (1.7-6.7%) were also detected in flying cranes. Surprisingly, some of the detected crops were not grown in the Kushiro and Nemuro regions. There was no significant difference in crop intake status in winter and that in other seasons for most of the crops. Corn (28.0%), soybeans (8.0%), wheat and beet (4.0%) were detected in crane chicks in summer, though the detection rates were generally lower than those in flying cranes. Alfalfa, which is not grown in eastern Hokkaido but is used in some cattle feed, was detected in some cranes. Rice, buckwheat, adzuki beans, common beans, potatoes and carrots were not detected at any life stage, indicating the preferences of red-crowned cranes. The results suggest that red-crowned cranes in Hokkaido are dependent on dairy farmers for their feed supply.

Interval of Remigial Molt of Two Wild Red-crowned Cranes<i>Grus japonensis</i> Breeding in Naganuma, Hokkaido, Japan

Molts of remiges of two wild Red-crowned Cranes Grus japonensis were observed in Maizuru retarding basin, Naganuma, Hokkaido. The female (A1) started to first molt in May 2019 when she was 2-years-old, and then molted two years later in June 2021. The male (A2) molted first in May 2018 when he likely was 2-years-old, and then molted three years later in June 2021 when he was raising a chick together with A1. The exact flightless period was uncertain, however, it was 45–56 days in A1, and 51–63 days in A2.

Conventional Gel Electrophoresis-Resolvable Insertion/Deletion Markers for Individual Identification and Analysis of Population Genetics in Red-Crowned Cranes in Eastern Hokkaido, Japan.

Simple SummaryThe red-crowned crane is an endangered bird species in the Far East Eurasian continent and Hokkaido, Japan. Individual identification has been achieved with banding and installed transmitters in only a few cranes, though individual identification is essential for various assessments of cranes on their behavioral characteristics, for example. An insertion/deletion (InDel) mutation is a mutation ranging from 1 to 50 bp and is very useful for genetic studies. If primer sets across InDels (>20 bp) can be designed, an InDel polymorphism can be determined with conventional agarose gel electrophoresis, as reported in some plant species. We found a sufficient number of InDel primer sets to be used for individual identification and analysis of population genetics of red-crowned cranes in Hokkaido. The method has additional advantages, such as convenience and low cost, without sequencing and an expensive apparatus.Red-crowned crane Grus japonensis is an endangered species in two separate populations: the mainland population in the Eurasian continent and the island population in eastern Hokkaido, Japan. We found 11 insertion/deletion (InDel) markers in the genome of the red-crowned crane and designed primer sets across these InDels that can be analyzed with conventional agarose gel electrophoresis. Sixty-six samples of whole blood and skeletal muscle obtained from red-crowned cranes, including 12 families in eastern Hokkaido from 1994 to 2021, showed different patterns in gel images of 11 InDel PCR reactions except for two pairs. The combined non-exclusion probability of the 11 markers indicates that individuals can be determined with a probability of 99.9%. In 39 non-relative chicks, the expected heterozygosity (He) was 0.316, suggesting low genetic diversity. This might not be caused by high levels of inbreeding since the average FIS was not significantly different from zero (0.095, p = 0.075). The results suggest that the 11 InDel primer sets can be used for fairly accurate individual identification as well as genetic population analyses in red-crowned cranes in the island population.

Comparison of 3D-printed Titanium Alloy and Polyether Ether Ketone Prosthetic Beaks for an Injured Red-crowned Crane (Grus japonensis).

The red-crowned crane (Grus japonensis) is a critically endangered species. Three-dimensional-printed prosthetic beaks made of titanium alloy and polyether ether ketone (PEEK) were used to repair the beak of a red-crowned crane that had a complete fracture of the anterior maxillary bone and rhinotheca. The physical properties and stability of the prostheses and changes in the crane's behaviors after application of either beak were evaluated. The titanium alloy and PEEK prosthetic beaks weighed 30.81 g and 5.9 g, respectively. Scanning electron microscopy showed differences in microstructure between the 2 materials and the true beak; the true beak was softer than both materials from which the prostheses were made. The titanium beak frequently detached, and the residual natural beak showed significant cuticle softening with this prosthetic beak. The titanium beak detached within an approximately 3-month period after placement, whereas the PEEK prosthetic beak has remained secure for 2 years. Moreover, the crane's foraging times (P < .01) and grooming times (P < .05) with the titanium alloy false beak were lower than the normal, red-crowned crane. With the PEEK beak, no detachment or cuticle softening occurred, and foraging and grooming behaviors were evaluated by the investigators as natural (P > .05). Based on the results of this clinical case, the PEEK prosthetic beak was found to be superior to the titanium alloy prosthetic beak in color, weight, firmness, and postoperative effects.

Metabarcoding of feces and intestinal contents to determine carnivorous diets in red-crowned cranes in eastern Hokkaido, Japan.

The red-crowned crane Grus japonensis in Hokkaido, Japan forms a closed population as a residence that is independent of the mainland population. Based on observations of a limited number of individuals as well as cranes in captivity, red-crowned cranes are omnivores and eat fish, worms, insects and plants in their own territories except in winter, when they are fed with dent corn that is supplied in eastern Hokkaido. DNA metabarcoding based on high throughput sequencing was carried out using universal primer sets for cytochrome oxidase subunit I gene. Feces from 27 chicks collected in June and July in the period from 2016 to 2018 and intestinal contents from 33 adult and subadult cranes that were found dead almost throughout year in 2006–2013 in the field in eastern Hokkaido were used. Although compositions varied considerably in the cranes, both insects and fish were found in adults and subadults to the same extents, while insects were predominant in chicks. Both insects and fish were detected in all seasons for adults and subadults. Horse flies, scarab beetles and weevils accounted for the most of the insects regardless of the life stage. Dace, stickleback, flatfish and sculpin were the major fish species in adults, while chicks ate almost only stickleback. The results provide the first comprehensive data on carnivorous diets in wild red-crowned cranes in eastern Hokkaido as basis for conservation of red-crowned cranes, for which the life style and area continue to change.

Origin of a pair of red-crowned cranes (Grus japonensis) found in Sarobetsu Wetland, northwestern Hokkaido, Japan: a possible crossbreeding between the island and the mainland population.

Red-crowned cranes Grus japonensis, which are an endangered species, have two separate populations, a mainland population in the Eurasian continent and an island population in eastern Hokkaido, Japan. Island cranes showed three haplotypes (Gj1, Gj2 and Gj13), whereas ten haplotypes (Gj3–Gj12) were confirmed in captive cranes and stray cranes. We found Gj5 haplotype in feathers of two cranes as well as four new haplotypes in seven wild crane feathers collected in South Korea. We also found feathers in the nest in Sarobetsu Wetland in northwestern Hokkaido. While the haplotype of female-derived feathers was Gj2, that of male-derived feathers was Gj5. The results suggest that there has been crossbreeding between cranes in the island population and cranes in the mainland population.

Comprehensive transcriptome characterization of Grus japonensis using PacBio SMRT and Illumina sequencing

The red-crowned crane (Grus japonensis) is an endangered species distributed across southeast Russia, northeast China, Korea, and Japan. Here, we sequenced for the first time the full-length unreferenced transcriptome of red-crowned crane mixed samples using a PacBio Sequel platform. A total of 359,136 circular consensus sequences (CCS) were obtained via clustering to remove redundancy. A total of 303,544 full-length non-chimeric sequences were identified by judging whether CCS contained 5′ and 3′ adapters, and the poly(A) tail. Eight samples were sequenced using Illumina, and PacBio sequencing data were corrected according to the collected Illumina data to obtain more accurate full-length transcripts. A total of 4,100 long non-coding RNAs, 13,115 simple sequences repeat loci and 29 transcription factor families were identified. The expression of lncRNAs and TFs in pancreas was lowest comparing with other tissues. Many enriched immune-related transmission pathways (MHC and IL receptors) were identified in the spleen. This study will contribute to a better understanding of the gene structure and post-transcriptional regulatory network, and provide references for future studies on red-crowned cranes.

Avian Surveys in the Korean Inner Border Area, Gimpo, Republic of Korea.

BackgroundBirds are useful environmental indicators as their presence reflects the health of the food web. Bird occurrence, rarity and abundance are reliable indicators of ecosystem health. Monitoring of avian populations in the Republic of Korea (ROK) is a primary requirement due to plummeting populations and the risks to threatened species. The Ministry of Environment of ROK started conducting winter bird censuses in 1999, including inland areas and coast areas, such as Cheorwon, Yeoncheon, Junam Reservoir and Han River. Cheolwon, Yeoncheon and some extent islands in the West Sea have been survey extensively due to iconic bird species, such as White-naped Crane (Grus vipio) or Red-Crowned Crane (Grus japonensis) wintering there. However, the winter bird census has not covered Yu Islet, Han River Estuary. Yu Islet is located within the Han River Estuary, a protected wetland in the Neutral Zone between the two Koreas and north of Gimpo in the ROK. The Islet currently supports a large, mixed breeding colony of waterbirds, such as one of the nation’s largest concentration of breeding Great Cormorants (Phalacrocorax carbo) and smaller numbers of breeding Black-faced Spoonbill (Platalea minor), Grey Heron (Ardea cinereal), Great Egret (Ardea alba) and Intermediate Egret (Ardea intermedia). Access to the area has long been restricted for military reasons, but recently, regular survey activity is possible supported by Gimpo City and the military base in Gimpo from November 2018.New informationHere, we provide data demonstrating that Yu Islet is important for breeding for waterbirds; and that the northern Gimpo part of Han River Estuary is also internationally important for waterbirds during the migratory bird season, as defined by the Ramsar Convention (Ramsar 1971, RRC-EA 2017). In particular, four waterbird species were found during the survey in the Main Survey Area: Swan Goose (Anser cygnoides), Taiga Bean Goose (Anser fabalis), Tundra Bean Goose (Anser serrirostris) and Greater White-fronted Goose (Anser frontalis). Once considered widespread in East Asia and abundant, the world population of Swan Goose is now estimated at only 60,000 - 78,000 individuals (Wetlands International 2020) and the species is assessed by BirdLife International as globally Vulnerable (BirdLife International 2020). The 1,010 Swan Goose (Anser cygnoides) counted on the vegetated mudflats at Jogang-Ri in the Main Survey Area on 27 November 2018 represents more than 1% of the total world population of this species. Notably, it is also the highest count of this species in the ROK for at least a decade. The count confirms the continuing international importance of the Han River Estuary for the survival of the Swan Goose. The number counted in November had fallen to 250 by 28 December 2018; and none was recorded in the Main Survey Area in January or February 2019. Although searched for in March, none was noted during the northward migration either. The surveys also found small numbers of nationally-scarce Grey-capped Pygmy Woodpecker (Yungipicus canicapillus) in several areas of woodland surrounded by the Han River Estuary. By selecting the most species-rich count within a given month in each of the two survey sectors, the number of species we recorded ranged from a minimum 29 in January to a maximum of 65 in April 2019. Based on the species recorded, the survey area is clearly important for avian conservation. Its importance derives from the combination of the extensive areas of high-quality wetland and its geographic location within one of the Korea Peninsula’s largest and most important remaining wetland ecosystems, the Han River Estuary. Our surveys resulted in the detection of a substantial number of bird species, especially in March and April when forest-breeding birds are more obviously vocal. The survey result is provided in the supplementary material (Suppl. material 1).

Effects of Montmorillonite on Growth Performance, Serum Biochemistry and Oxidative Stress of Red-Crowned Crane (Grus japonensis) Fed Mycotoxin-Contaminated Feed.

The red-crowned crane (Grus japonensis) is one of the most vulnerable bird species in the world. Mycotoxins are toxic secondary metabolites produced by fungi and considered naturally unavoidable contaminants in animal feed. Our recent survey indicated that the mycotoxins had the potential to contaminate redcrowned crane's regular diets in China. This experiment was conducted to investigate the protective effects of mycotoxin binder montmorillonite (Mont) on growth performance, serum biochemistry and oxidative stress parameters of the red-crowned crane. 16 red-crowned cranes were divided into four groups and fed one of the following diets; a selected diet, regular diet, or the selected diet or regular diet with 0.5% montmorillonite added to the diets. The cranes' parameters of performance, hematology, serum biochemistry and serum oxidative stress were measured. Consuming regular diets decreased the average daily feed intake (ADFI), levels of haemoglobin (Hb), platelet count (PLT), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT), but increased the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine kinase (CK) and lactate dehydrogenase (LDH). The supplementation of 0.5% Mont provided protection for the red-crowned crane in terms of feed intake, serum biochemistry and oxidative stress. Moreover, Mont supplementation had no adverse effect on the health of red-crowned crane. Taken together, these findings suggested that the addition of dietary Mont is effective in improving the health of red-crowned crane.

Age of First Primary Moult in the Red-Crowned Crane Grus japonensis

The Red-crowned Crane Grus japonensis population of Hokkaido, Japan, has increased to over 1,600 individuals since near extinction in the late 19th and early 20th centuries. Adults and subadults can be distinguished by visible characteristics of their remiges; adults have pure white primaries whereas subadult birds have black primary tips and upper primary wing coverts. Banded individuals hatched during 2015–2017 were examined in detail using photographs and videos and it was found that the subadult characteristics of the remiges disappeared in individuals older than two years.

Red-Crowned Crane (Grus japonensis) Reproduction Was Improved by Inhibiting Mycotoxins with Montmorillonite in Feed.

The red-crowned crane (Grus japonensis) is a vulnerable bird species. Mycotoxins are toxic substances produced by filamentous fungi and are considered as naturally unavoidable contaminants in animal feed. Our recent survey indicated that feeds designed for captive red-crowned cranes were contaminated with mycotoxins. This study was conducted to investigate the protective effects of the mycotoxin binder montmorillonite on the reproductive behavior, sex hormone levels, and egg quality of red-crowned cranes. Twelve pairs of G. japonensis were divided into four groups, and each group was fed one of the following: a selected diet (with extra low levels of mycotoxins), a regular diet, a selected diet with 0.5% montmorillonite added, or a regular diet with 0.5% montmorillonite added. Consumption of the regular diet decreased courtship and mating behaviors, testosterone concentration, egg weight, and shell thickness. However, feed supplementation with montmorillonite increased the courtship, mating behaviors and testosterone concentration during the pre-breeding period, as well as egg weight and shell thickness. These findings suggest that the addition of dietary montmorillonite is effective for controlling mycotoxins in the feed, resulting in improvements in reproductive behaviors, testosterone concentrations, and some egg quality parameters of the red-crowned crane.

Breeding range shift of the red-crowned crane (Grus japonensis) under climate change.

The red-crowned crane (Grus japonensis) is an endangered species listed by International Union for Conservation of Nature (IUCN) HARRIS J (2013). The largest population of this species is distributed mainly in China and Russia, which is called continental population SU L (2012)-Curt D (1996). This population is migratory, which migrates from its breeding range located in Northeast China and Southern Russia, to the wintering range in the south of China to spend the winter every year. The breeding range of this species is critical for red-crowned crane to survive and maintain its population. Previous studies showed the negative effects of habitat loss and degradation on the breeding area of red-crowned crane Ma Z (1998), Claire M (2019). Climate change may also threat the survival of this endangered species. Previous studies investigated the impacts of climate change on the breeding range or wintering range in China Wu (2012), [1]. However, no study was conducted to assess the potential impacts of climate change on the whole breeding range of this species. Here, we used bioclimatic niche modeling to predict the potential breeding range of red-crowned crane under current climate conditions and project onto future climate change scenarios. Our results show that the breeding range of the continental population of red-crowned crane will shift northward over this century and lose almost all of its current actual breeding range. The climate change will also change the country owning the largest portion of breeding range from China to Russia, suggesting that Russia should take more responsibility to preserve this endangered species in the future.

Genetic diversity of wild wintering red-crowned crane (Grus japonensis) by microsatellite markers and mitochondrial Cyt B gene sequence in the Yancheng reserve

The red-crowned crane (Grus japonensis) is one of the most endangered cranes in the world, and its wild population is still declining. To characterize the genetic resources of East Asian migratory populations, we studied the genetic variation in wild red-crowned cranes at the Yancheng reserve. Based on a partial Cyt b gene sequence, 32 wild red-crowned crane samples were screened from 100 feathers with unknown sample information. Twelve haplotypes were detected using 32 wild red-crowned crane samples. Six pairs of published microsatellite primers were selected for genotyping. A total of 47 alleles were obtained, with an average of 7.8 alleles per locus. All microsatellite loci were highly polymorphic; the average polymorphic information content and expected heterozygosity were 0.721 ± 0.080 and 0.768 ± 0.071, respectively. These results show that the East Asian migratory population of wild red-crowned cranes exhibits high polymorphism. These data are useful for informing reintroduction efforts. The study results provide a basis for understanding the population genetic properties of an endangered crane.

Reinforcement Project and Breeding Cases of Introduced Endangered Red-Crowned Cranes Grus japonensis in Yancheng National Nature Reserve, China

The Red-crowned Crane Grus japonensis is an endangered species in East Asia. The western flyway population in China has been in steady decline in recent years because of the loss and deterioration of the natural wetland habitat it requires. To enhance this migratory Red-crowned Crane population, a project was designed to return captive Red-crowned Cranes to the wild in 2013 and 2015 in the Yancheng National Nature Reserve (YNNR). This reserve is the most important wintering site for the continental migratory population. The survival rate of introduced Red-crowned Cranes was 40%. However, aggregation of introduced and wild individuals was not observed. Introduced individuals did not pair with wild individuals nor did they migrate to breeding areas with them. They remained in the core zone of the YNNR over summer. Here, we report the first breeding of introduced Red-crowned Cranes in the YNNR in 2017 and 2018. Suitable rearing methods and the use of aircraft to inform them of the migration route are necessary. Further research is necessary to confirm the migratory status of the cranes that are reared in the reserve.

Hepatic transcriptional profile and tissue distribution of cytochrome P450 1-3 genes in the red-crowned crane Grus japonensis

The endangered red-crowned crane (Grus japonensis) is a protected species in eastern Hokkaido and injured specimens are treated with medication. The present study aimed at understanding the expression profiles of cytochrome P450 (CYP) 1-3 genes in red-crowned crane tissues. We used 14 individuals found dead in the wild in eastern Hokkaido or in Kushiro City Zoo. Nine CYP1-3 genes expressed in the liver of the red-crowned crane were identified by high-throughput sequencing, and phylogenetically classified as CYP1A5, CYP2C23, CYP2C45, CYP2D49, CYP2G19, CYP2U1, CYP2AC1, CYP3A37, and CYP3A80. Based on the quantitative real-time PCR of 13 samples, the rank order of their median expression levels was as follows: CYP3A37 > CYP2AC1 > CYP2C45 > CYP2D49 > CYP2G19 > CYP1A5 > CYP3A80 > CYP2C23. The tissue distribution of the CYP transcripts indicated that many of the CYP1–3 genes examined were mainly expressed in the tissues where drug metabolism occurs, such as the liver, kidneys, and lungs. We found that CYP3A37 was dominant at the transcript level in the liver, indicating it might play a crucial role in liver physiology and xenobiotic metabolism. Similarly, an “orphan” CYP2AC1 was expressed at relatively high levels in the kidneys and liver, suggesting a possible role in renal and liver physiology and xenobiotic metabolism. Our results establish a foundation for future studies on red-crowned cranes aiming to further understand drug sensitivity and develop medication protocols, but also contribute to national and local projects for the conservation of red-crowned crane.

Body size and first-winter survival of Red-crowned Crane Grus japonensis chicks

ABSTRACTAn analysis of the biometrics of 187 individually marked Red-crowned Crane Grus japonensis chicks from Japan revealed that larger chicks were more likely to seen alive in their first-winter. Male chicks were larger than females but sex did not influence apparent survival, nor did brood size determine body size.

First molecular detection and characterization of Marek\u2019s disease virus in red-crowned cranes (Grus japonensis): a case report

BackgroundMarek’s disease virus (MDV) resides in the genus Mardivirus in the family Herpesviridae. MDV is a highly contagious virus that can cause neurological lesions, lymphocytic proliferation, immune suppression, and death in avian species, including Galliformes (chickens, quails, partridges, and pheasants), Strigiformes (owls), Anseriformes (ducks, geese, and swans), and Falconiformes (kestrels).Case presentationIn 2015, two red-crowned cranes died in Nanjing (Jiangsu, China). It was determined that the birds were infected with Marek’s disease virus by histopathological examination, polymerase chain reaction (PCR), gene sequencing and sequence analysis of tissue samples from two cranes. Gross lesions included diffuse nodules in the skin, muscle, liver, spleen, kidney, gizzard and heart, along with liver enlargement and gizzard mucosa hemorrhage. Histopathological assay showed that infiltrative lymphocytes and mitotic figures existed in liver and heart. The presence of MDV was confirmed by PCR. The sequence analysis of the Meq gene showed 100% identity with Md5, while the VP22 gene showed the highest homology with CVI988. Furthermore, the phylogenetic analysis of the VP22 and Meq genes suggested that the MDV (from cranes) belongs to MDV serotype 1.ConclusionWe describe the first molecular detection of Marek’s disease in red-crowned cranes based on the findings previously described. To our knowledge, this is also the first molecular identification of Marek’s disease virus in the order Gruiformes and represents detection of a novel MDV strain.

Duet displays within a flock function as a joint resource defence signal in the red-crowned crane

Avian duets performed in an exclusive territory have been studied intensively. By contrast, only a few studies have been conducted on duets with multi-modal displays performed within a fission–fusion flock in which individuals can participate in face-to-face social interactions. Here, we examined the duet displays (DDs) of the red-crowned crane (Grus japonensis), an endangered species in Japan, in a wintering flock in which individuals gathered for artificially provisioned foods. We tested two hypotheses: that DDs function as a signal of joint resource defence and for pair bond maintenance. Our behavioural analyses showed that the total frequency of DDs within a flock was positively associated with the number of joining cranes. This result indicated that the change in within-flock competition positively affected DD performance because an increase in flock size can reduce the per capita gain of resources. At the individual level, pairs accompanying their young (families) performed DDs more frequently than pairs that did not have their young. To care for their young, access to food resources is thought to be more important for pairs accompanying their young than pairs that did not have young. This result suggests that the DDs reflected the motivation to compete for resources. The performance of DDs increased the probability of staying in a favourable area. These results support the hypothesis that DDs function as a signal of joint resource defence in the flock. This study provides rare data on the function of coordinated vocal displays within a flock of birds. Crane pairs perform duet displays (DDs) in a wintering flock. We mainly tested the hypothesis that DDs function as a joint resource defence signal. The change of overall competition positively affected the frequency of DDs, and the performance of DDs reflected the motivation to access food. The frequency of DDs was positively associated with the success of the food defence. This study provides rare data on the function of coordinated vocal displays within a group of birds.