Avian Research最新文献

{"title":"From fledging to independence: Post-fledging movements and space use of the Crested Ibis (Nipponia nippon)","authors":"Yu Lei ,&nbsp;Xianglong Xu ,&nbsp;Yuanxing Ye ,&nbsp;Chao Wang ,&nbsp;Baoping Qing ,&nbsp;Wenbin Duan ,&nbsp;Jiaqi Yan ,&nbsp;Yongjie Huang ,&nbsp;Changqing Ding","doi":"10.1016/j.avrs.2025.100266","DOIUrl":"10.1016/j.avrs.2025.100266","url":null,"abstract":"<div><div>The post-fledging period, extending from fledging to independence, is a crucial life stage characterized by high mortality due to fledglings' limited mobility and inexperience. During this stage, fledglings gradually increase their mobility, leave their parents, disperse from their natal site, and respond to the challenges of new environments. Characterizing these post-fledging movements and space use is essential for understanding juvenile survival strategies and devising targeted conservation measures. The Crested Ibis (<em>Nipponia nippon</em>), an endangered species and a highly protected animals at the national level in China, has seen limited research on its post-fledging movements and space use. From 2015 to 2023, we utilized biologgers, combined with field surveys, to study the movement and space use characteristics of 37 fledglings in Hanzhong City, Shaanxi Province, China, over a two-month post-fledging period. We quantified changes in activity levels (based on overall dynamic body acceleration), independence timing, onset of post-fledging dispersal, habitat selection, and daily activity rhythms after independence. Our results revealed individuals began independent living 26.23 ± 2.34 days post-fledging and onset of dispersal at 25.58 ± 2.33 days, with a range area at the natal of 2.08 ± 0.56 km². The initial 30 days post-fledging are characterized as an ontogenetic phase marked by a rapid increase in body activity level. Fledglings preferred paddy fields during the independent period rather than the forests they relied on before independence. Interestingly, the daily activity rhythm, particularly foraging behavior, peaked at noon—contrasting with the expected morning and evening activity peaks—likely as an adaptation to avoid periods of peak human activity. Additionally, drowning, collisions, and predation in paddy fields are noteworthy causes of fledgling mortality. Consequently, we recommend protecting a 2-km² area around the nest site for at least two-month post-fledging, implementing safety measures around power lines and cesspools. Additionally, reducing human disturbances near foraging habitats and expanding space within paddy fields would help mitigate survival pressures on fledglings.</div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100266"},"PeriodicalIF":1.6,"publicationDate":"2025-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144330817","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sri Lanka's laughingthrush: An ecological and phylogenetic assessment of a babbler confused for a laughingthrush","authors":"Dileka Kariyawasam,&nbsp;Gihan D. Jayasinghe,&nbsp;Janaka Perera,&nbsp;Sampath S. Seneviratne","doi":"10.1016/j.avrs.2025.100269","DOIUrl":"10.1016/j.avrs.2025.100269","url":null,"abstract":"<div><div>The Ashy-headed Laughingthrush (<em>Argya cinereifrons</em>), a species endemic to Sri Lanka, has been historically considered a laughingthrush in the genus <em>Garrulax.</em> However, based on phylogenetic evidence, recent studies have suggested a new classification for the species under the genus <em>Argya</em> (true babblers). Despite the genetic signal showing affinity to true babblers <em>Argya</em>, as its common name suggests, the Ashy-headed Laughingthrush (AHLT) shows remarkable morphological similarities to other laughingthrushes of the Indo-Himalayan region. Here we attempted to address this incongruence in phenotypic and phylogenetic signals in this species by reconstructing the molecular phylogeny of babblers and comparing that with the key morphological, plumage, and vocal features of the two concerned groups. We hypothesized that the convergence of phenotype and vocalization of <em>Garrulax</em> in the wet evergreen forests of the Indian mainland and AHLT in the wet tropical rainforests of southern Sri Lanka has historically confused the taxonomists. The phylogenetic relationships were reconstructed using Bayesian inference using four mitochondrial and seven nuclear gene regions. The molecular phylogenetic tree placed the AHLT with India's Large Grey Babbler (<em>A. malcolmi</em>) as the sister taxon within the genus <em>Argya</em>. The hierarchical clustering based on body size, shape, plumage colour, and vocal properties resulted in the inconsistent placement of ALTH with babblers or laughingthrushes. Therefore, an incongruence in phenotype and genotype is observed. Our findings show that the convergent patterns of phenotypic evolution can confuse both historic and recent taxonomic delimitations in highly divergent groups such as Asian babblers.</div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100269"},"PeriodicalIF":1.6,"publicationDate":"2025-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144501477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"How nestlings of Oriental Reed Warbler respond to adult alarm calls","authors":"Jiaojiao Wang ,&nbsp;Yongrui Feng ,&nbsp;Laikun Ma ,&nbsp;Longwu Wang ,&nbsp;Canchao Yang ,&nbsp;Jianhua Hou","doi":"10.1016/j.avrs.2025.100270","DOIUrl":"10.1016/j.avrs.2025.100270","url":null,"abstract":"<div><div>Avian alarm calls mediate defenses against brood parasites and predators. These calls facilitate communication among adults and alert nestlings to potential danger. While heterospecific call recognition has been extensively studied in adult birds, nestlings—lacking direct predation experience and heterospecific alarm exposure—represent an ideal system to investigate the response to interspecific warning cues. This study explored the recognition capabilities of 5–6-day-old nestlings in Oriental Reed Warbler (<em>Acrocephalus orientalis</em>), a common host of the Common Cuckoo (<em>Cuculus canorus</em>). We exposed the nestlings to playbacks of alarm calls directed at parasites and raptors from conspecific, Vinous-throated Parrotbill (<em>Sinosuthora webbiana</em>, sympatric species), Isabelline Shrike (<em>Lanius isabellinus</em>, allopatric species) and Common Tailorbird (<em>Orthotomus sutorius</em>, allopatric species) adults. Results indicated that there was no significant difference in the responses of nestlings to the alarm calls of conspecific and allopatric adults directed at cuckoos and sparrowhawks. In addition, interestingly, nestlings significantly reduced their begging in response to conspecific and unfamiliar allopatric Isabelline Shrike and Common Tailorbird alarm calls but exhibited a weak response to the sympatric Vinous-throated Parrotbill. Whether older warbler nestlings with more social experience exhibit stronger responses to the alarm calls of Vinous-throated Parrotbill adults requires further investigation.</div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100270"},"PeriodicalIF":1.6,"publicationDate":"2025-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144306881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multi-dimensional niche segregation of sympatric breeding seabirds in the Xisha Archipelago","authors":"Yuanyuan Zhao ,&nbsp;Yangfei Yu ,&nbsp;Yunteng Liu ,&nbsp;Lei Zhu ,&nbsp;Zhikai Liao ,&nbsp;Yuelou Liu ,&nbsp;Jian Su ,&nbsp;Yilin Deng ,&nbsp;Siqi He ,&nbsp;Cheng Wenda ,&nbsp;Yachang Cheng ,&nbsp;Yang Liu","doi":"10.1016/j.avrs.2025.100268","DOIUrl":"10.1016/j.avrs.2025.100268","url":null,"abstract":"<div><div>Studying coexistence mechanisms is practically important for understanding and conserving marine biodiversity and community structure. Tropical marine ecosystems may exhibit higher competition between top predators due to generally low primary productivity and pronounced seasonal fluctuation in food availability. Consequentially, niche segregation in sympatric breeding seabirds is expected to occur as a mechanism to maintain species coexistence. However, a single-dimensional study on seabird niche segregation might result in unclear niche overlap. Here, we investigated multi-dimensional niche segregation of tropical seabirds during field expeditions to the Xisha Archipelago, China, in 2023. We reconfirmed the breeding status of six species of terns and noddy, and further revealed the multi-dimensional niche segregation among Black-naped (<em>Sterna sumatrana</em>), Bridled (<em>Onychoprion anaethetus</em>) and Roseate (<em>Sterna dougallii</em>) Terns. Spatially, these three species utilized nest sites that differentiated by vegetation and distance to sea. Temporally, Black-naped Terns bred earlier and for a longer period, while Bridled and Roseate Terns had more restricted breeding seasons. Furthermore, the daily foraging activity patterns of these species also differed, with Bridled Terns potentially having a longer foraging time at noon. In terms of diet, Bridled Terns were opportunists that fed on fishes, squids and insects, such as migratory fruit-piercing moths, while Roseate Terns were primarily piscivorous, especially feeding on Exocoetidae (flying fishes). Seabirds play a crucial role in marine ecosystems and are globally threatened. Our findings shed light on the complex mechanisms facilitating the coexistence of sympatric seabird species in China. Further research is needed to examine other ecological interactions and to develop effective conservation strategies for protecting these valuable seabird populations.</div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100268"},"PeriodicalIF":1.6,"publicationDate":"2025-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144279351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of sterile apices of Puya chilensis (Bromeliaceae) on the nectar-feeding behavior of passeriform birds in central Chile","authors":"Natalia Ugas-Bravo,&nbsp;Pilar Guerrero,&nbsp;Rodrigo Medel","doi":"10.1016/j.avrs.2025.100267","DOIUrl":"10.1016/j.avrs.2025.100267","url":null,"abstract":"<div><div>The factors affecting the behavior of non-specialized nectar-feeding passerines have received little attention in the literature on plant-pollinator interactions. <em>Puya chilensis</em> (Bromeliaceae) has sterile branch apices that project outward from the inflorescence. In this study, we evaluate the functional role of sterile apices as support systems for bird foraging behavior. We recorded bird visitation and flower probing in the presence and absence of sterile branches during the spring seasons of 2021 and 2024. The results revealed that experimental plants with excised branches received fewer bird visits and flower probings than control plants, indicating that sterile branches play an important role in the nectar-feeding behavior of passerine birds in <em>P. chilensis.</em></div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100267"},"PeriodicalIF":1.6,"publicationDate":"2025-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144242306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Variation of migration routes in the central Asian-breeding Common Cuckoo population influenced by the Qinghai-Tibet Plateau","authors":"Zhichang Cheng ,&nbsp;Donghui Ma ,&nbsp;Mengjie Lu ,&nbsp;Xingnan Du ,&nbsp;Lingwang Kong ,&nbsp;Xinkang Bao","doi":"10.1016/j.avrs.2025.100265","DOIUrl":"10.1016/j.avrs.2025.100265","url":null,"abstract":"<div><div>Ecological barriers present significant challenges to bird migration by limiting the availability of stopover sites and shelters. The Qinghai-Tibet Plateau, a major migratory barrier located in higher latitude Central Asia, exerts a substantial influence on avian migration patterns. Species traversing such ecological barriers may adopt multiple optimal routes, which can contribute to the formation of migratory divides. From 2018 to 2021, the migration routes of 13 adult Common Cuckoos (<em>Cuculus canorus</em>) breeding in the north of the Qinghai-Tibet Plateau were tracked using satellite transmitters. We found Common Cuckoos have two primary migration routes: western and eastern, respectively following western and eastern edges of the Qinghai-Tibet plateau. The eastern and western routes are likely the optimal routes for the Central Asian Common Cuckoos population to navigate the Qinghai-Tibet Plateau. Furthermore, two individuals exhibited intermediate migration routes, suggesting attempted traverses of the Qinghai-Tibet Plateau, although neither completed the migration. These intermediate routes may indicate migratory behavior influenced by hybridization between eastern and western populations or migratory flexibility. Common Cuckoos exhibit significantly faster migration speed, flight speed, and shorter stopover durations during spring compared to autumn. The observed seasonal differences in migration behavior support birds following time-minimization strategies during spring migration. These results revealed the diverse migration routes of Common Cuckoos shaped by the Qinghai-Tibet Plateau and seasonal variation in migration patterns.</div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100265"},"PeriodicalIF":1.6,"publicationDate":"2025-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144229668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transcontinental evolutionary dynamics and phylogeography of Alectoris (Aves: Galliformes): Identifying refugia, dispersal corridors, and cryptic diversity in the Palearctic region","authors":"Bekir Kabasakal ,&nbsp;Huriye Doğru ,&nbsp;Ali Erdoğan ,&nbsp;Sarp Kaya","doi":"10.1016/j.avrs.2025.100262","DOIUrl":"10.1016/j.avrs.2025.100262","url":null,"abstract":"<div><div>The <em>Alectoris</em> (Galliformes: Phasianidae) has a wide distribution range in the Palearctic region, with seven species and 27–31 subspecies that were distinguishable by minor morphological differences. The members of the genus exhibit distinct genetic structuring compatible with geography due to their inability to make long flights and ground-dwelling behaviors. In this respect, the evolutionary history of the genus and its populations is a useful tool for identifying potential cryptic refugia, dispersal corridors, and strong barriers for bird species in the Palearctic region. On the other hand, wild populations of the genus are among the bird species most affected by human activities. For this purpose, sequences from the mitochondrial D-loop and Cyt-<em>b</em> regions of individuals from the genus <em>Alectoris</em> were studied to identify the evolutionary history of the genus, determine potential cryptic species, and reveal possible hidden diversification areas in the Palearctic region. The results indicated that: the Mediterranean basin is the ancestral area of the <em>Alectoris</em>, there are two main diversification centers within its distribution range (Mediterranean Basin and China) of the genus, and certain micro-refugia and permanent dispersal corridors have been observed in Eastern Palaearctic region. Additionally, the results showed that the Pleistocene climatic changes acted as a species pump, playing a significant role in the diversification of lineages within the genus. Anatolia served as the ancestral area for the <em>A. chukar</em> and acted as a bridgehead during the species' dispersal in the inner side of the Eastern Palaearctic. High mountain ranges, monsoonal climate types, and deserts in the Eastern Palearctic played a significant role in the dispersal and diversification of the ancestral <em>A. chukar</em> population. Importantly, human activities appear to be the greatest evolutionary force shaping the future evolution of the genus.</div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100262"},"PeriodicalIF":1.6,"publicationDate":"2025-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144321561","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Phylogeography of the endangered Yellow-headed Parrot (Amazona oratrix)","authors":"Melquicedec Escalante-Vargas ,&nbsp;Patricia Escalante-Pliego","doi":"10.1016/j.avrs.2025.100259","DOIUrl":"10.1016/j.avrs.2025.100259","url":null,"abstract":"<div><div>Elucidating the historical processes that led populations to their current spatial and genetic arrangement is relevant in conserving threatened species. We interpreted the phylogeographic structure of the threatened Yellow-headed Parrot (<em>Amazona oratrix</em>) with mitochondrial markers and analyzed 98 samples from Mexico, Guatemala, and Belize. We performed analyses of genetic structure, genealogical relationships, demographic history, and divergence times and illustrated the phenotypic variation qualitatively of the sampled individuals. The studies revealed that 92% of the genetic variation is explained between the Mexican Tres Marías Islands, the Mexican Pacific Coast, and the Atlantic groups. These three groups were segregated into two main lineages (Pacific and Atlantic), separated by 26 mutations, leaving <em>A</em>. <em>auropalliata</em> within the Atlantic. We found that both lineages diverged 0.55 million years ago, from which the Atlantic lineage experienced population expansion, high levels of genetic diversity, and a low genetic structure with two phenotypes. The Pacific experienced demographic stability, low levels of diversity, and a genetic structure marked with two phenotypes. Our estimates indicate that this separation occurred in the Pleistocene when the Atlantic clade diverged from Panama and dispersed overland to the Gulf of Mexico. Simultaneously, the Pacific clade departed from the same area to Tres Marías Islands and the Mexican Pacific coast. We deduce that this long-distance event was probably produced by assisted dispersal, but other scenarios appear more parsimonious. We conclude that there is no gene flow between both lineages and that the phylogeographic structure resulted significantly from historical events and climatic changes during the Pleistocene. We propose undertaking other analyses in the future to compare our results and the paraphyletic relationships in <em>A. oratrix.</em></div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100259"},"PeriodicalIF":1.6,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144107497","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Highway effects on artificial nest survival in a neotropical sand-coastal plain: A spatiotemporal approach","authors":"Gleidson Ramos da Silva ,&nbsp;Pedro Diniz ,&nbsp;Charles Duca","doi":"10.1016/j.avrs.2025.100264","DOIUrl":"10.1016/j.avrs.2025.100264","url":null,"abstract":"<div><div>Roads are a leading cause of habitat fragmentation and may reduce bird populations by increasing nest predation rates. However, few studies have investigated the effects of traffic volume on the reproductive success of roadside birds in the neotropics. Our goal was to evaluate the effects of spatial, temporal, and vehicle flow variations on the survival of artificial open-cup nests. The study was carried out in a nature reserve on the side of a highway during the breeding season (from October to March) in two restinga (sand-coastal plain) phytophysiognomies in southeastern Brazil: non-floodable (open) and floodable (closed). One hundred thirty nests were distributed along transects ranging from 3 m to 300 m from the highway in each vegetation type (totaling 260 nests). The nests were checked every three days for their status (depredated or intact) over 12 days, and new nests were subsequently placed near sampling points of depredated or successful nests. We estimated survival using logistic exposure generalized linear and additive mixed models. At the end of the 180 days of the experiment, 33% of 6202 nests were successful. Nest survival was higher in open restinga than in closed restinga. In both habitats, nest survival was lowest mid-season and highest at the beginning and end. Survival rates peaked near the highway, declined up to 50 m away, then showed a slight increase. Finally, survival increased at moderate-to-high traffic volumes (∼22,000 vehicles/day), particularly in open restinga. We suggest that spatial, temporal, and habitat-specific highway impacts (e.g., noise, vibration, visual stimuli) can lead to variations in the activity of nest predators, generating fluctuations in nest survival associated with predator behavior.</div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100264"},"PeriodicalIF":1.6,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144139578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reconciling Bergmann's rule throughout the annual cycle in two congeneric large-bodied migratory waterbirds","authors":"Dehai Gu ,&nbsp;Yanbo Xie ,&nbsp;Tetsuo Shimada ,&nbsp;Hiroyoshi Higuchi ,&nbsp;Diana Solovyeva ,&nbsp;Inga Bysykatova-Harmey ,&nbsp;Yanlei Liu ,&nbsp;Junjian Zhang ,&nbsp;Qingshan Zhao ,&nbsp;Lei Cao ,&nbsp;Anthony D. Fox","doi":"10.1016/j.avrs.2025.100263","DOIUrl":"10.1016/j.avrs.2025.100263","url":null,"abstract":"<div><div>Bergmann's rule predicts that the larger of two homeotherm species differing only in size would occur at higher latitudes, or in cooler climates than the smaller, because of relative thermoregulatory costs in relation to body mass/surface area ratio. Individual tracking data from two congeneric long-distance migratory northern nesting swan species, Tundra <em>Cygnus columbianus</em> (TS, <em>n</em> = 99) and Whooper Swans <em>C. cygnus</em> (WS, 61–71% larger mass than TS, <em>n</em> = 47) were used to determine their summering and wintering latitudes along similar migration routes and common staging areas along the same flyway. We hypothesised that throughout Arctic and Boreal breeding areas (10 °C in July), summer ambient temperatures mainly exceed the Lower Critical Temperatures (LCT, c. 1 °C) for both swan species, so the duration of the snow-free summer period will favour smaller body size at highest latitudes, since this constrains the time available to lay, incubate eggs and raise cygnets to fledging. We hypothesised that in contrast, in winter, both species occur in temperatures near to freezing (−3 °C in January), below their respective LCT, so differential thermoregulation demands would constrain TS to winter south of WS. Tracking of individuals showed for the first time that while smaller TS summered significantly north of WS, WS wintered significantly north of TS, with limited overlap in both seasons. We conclude that differences in relative summer distribution of these two closely related migratory herbivores are not to do with latitude <em>per se</em> but are constrained by the time both species require to raise their young to fledging during the short northern summer, when thermoregulation costs are unlikely limiting. In winter, both swan species occur within a climate envelop at or below their respective LCT and smaller TS occurred consistently south of the range of the tracked WS, as predicted by Bergmann's rule.</div></div>","PeriodicalId":51311,"journal":{"name":"Avian Research","volume":"16 3","pages":"Article 100263"},"PeriodicalIF":1.6,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144147305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}