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In 2017, one pair of Oriental reed warblers (Acrocephalus orientalis) with color aberrations was found in Yongnianwa National Wetland Park, Hebei, China. The female bird exhibited white feathers on the head, neck, and upper back, and the base of the beak was flesh‐red in color. The male had a few feathers on the outer edges of the left and right primary wing coverts that were white, which was determined to be leucism after analysis. The breeding pairs laid their first egg on May 29, with a clutch size of four eggs. After an incubation period of 13 days, two chicks hatched on June 13, 2017. The nest was found empty on June 20 when the chicks were 7 days old and before fledging age; therefore, it was presumed that the chicks had been predated. A white parrot egg was added to the nest during the incubation period to test the egg recognition ability of breeding pairs and was successfully rejected. To the best of our knowledge, this is the first report of color aberrations in the Oriental reed warbler, and we found that this color aberrations did not affect some reproductive and antiparasitic behaviors of the birds, but whether it affects their breeding success needs to be further studied. [ABSTRACT FROM AUTHOR]

The species-specific and age-related autumn migration strategies of the sedge, reed and great reed warbler were investigated at stopover sites between central Europe and north-eastern Africa during autumn. Adult reed warblers accumulated larger fat reserves than juveniles and consequently were able to cover longer distances from most stopover sites. Juvenile sedge warblers, on the other hand, left Europe with significantly larger fat reserves than adults as opposed to the populations migrating along the western route. Both juvenile and adult great reed warblers were potentially able to make long flights without refuelling from the northern part of the Mediterranean region onwards. It was the proximity of large ecological barriers that had the most prominent influence on the potential flight distances of adult and juvenile Acrocephalus warblers during their southward migration. In reed and sedge warblers, the differences in mean flight distances covered by adults and juveniles were the largest (ca. 600 km) just before the crossing of the Mediterranean Sea, but smaller (ca. 200 and 400 km, respectively) in front of the Sahara Desert. Juvenile and adult great reed warblers were potentially able to cover 1660 km from Turkey, which was also supported by very low numbers of individuals caught at the Egyptian ringing sites. The results of this study carried out in the key regions of the eastern European–African flyway documented that migration strategies differed between adults and juveniles of three long-distance migrant species, yet this variation depended on the migration stage and the proximity of natural ecological barriers. [ABSTRACT FROM AUTHOR]

Alternative mating strategies, involving mating outside a social pair bond, have been studied intensively during the last few decades. However, we are still far from understanding what factors affect their frequencies in wild bird populations. In 2006–2011 we studied Eurasian Reed Warblers breeding in the nature reserve "Stawy Milickie" in SW Poland, and analysed the frequency of extra-pair paternity (EPP) and intra-specific brood parasitism (IBP). We genotyped a total of 786 nestlings from 259 nests. EPP offspring constituted 13.40% of all young (from 7.63% to 22.82% in different study years), and they were found in 21.62% of the broods (from 14.6% to 32.7% annually). The mean proportion of females with EPP young was 24.2% (from 16.2 to 41.7% annually). The proportion of EPP young in nests containing any EPP offspring ranged from 25% to 100% (on average 60%) and was not related to brood size. EPP young in one nest were sired usually by one or two males (92% of all cases), but we recorded one brood with three EPP fathers and one brood of four, where each young was sired by a different EPP male, and none by a social male. We found only one case of intra-specific brood parasitism (IBP). The brood with IBP constituted 0.39% of all examined broods, while the nestling that hatched from the dumped egg constituted 0.13% of all young whose parents were genotyped. We conclude that extra-pair paternity is a relatively common and regularly occurring alternative mating strategy in our study population of Reed Warblers, while intra-specific brood parasitism is extremely rare. [ABSTRACT FROM AUTHOR]

In predator–prey interactions, the prey faces extreme challenges from predation, which drives the evolution of defense or anti‐predator mechanisms. Compared with adult birds, nestlings are more vulnerable but not helpless. However, data on whether nestlings eavesdrop on the danger signals transmitted by other prey nestlings and the mechanisms of eavesdropping remain limited. In brood parasitism, common cuckoo (Cuculus canorus) nestlings, raised by host adults who are not closely related, offer an instructive system for studying the transmission and recognition of danger signals among nestlings of different species that share special relationships. We played back the distress calls of common cuckoo nestlings to nestlings of three sympatric host species (the oriental reed warbler Acrocephalus orientalis, which is a primary host of the common cuckoo, the reed parrotbill Paradoxornis heudei, an occasional host, and the vinous‐throated parrotbill Sinosuthora webbiana, which is not parasitized in the study area) to investigate whether the host nestlings reduced their begging behavior. We also quantified the degree of inhibition toward begging behavior for these nestlings. The results revealed that, in response to the distress calls, the three sympatric host species markedly suppressed their begging behavior. This response can likely be attributed to the innate response of host nestlings caused by the general characteristics of distress calls, rather than the acoustic similarity and phylogenetic relationship between host nestlings and cuckoo nestlings. Furthermore, we observed that upon hearing the distress calls of cuckoo nestlings, the oriental reed warbler nestlings exhibited the greatest reduction in the total number of calls compared to the other two host species, potentially owing to stronger predation and parasitic pressures. This study suggests that host nestlings can detect danger signals emitted by parasitic nestlings; however, further investigation is needed to determine whether they can respond to distress calls from unfamiliar nestlings in different regions. [ABSTRACT FROM AUTHOR]

Song complexity has been identified as one song characteristic important in female choice, whereas its role in male-male interactions is less clear and not much is known which song characteristics are specifically important for territorial defense. In Acrocephalus warblers, males seem to increase song complexity towards females but reduce it during territorial disputes. One possibility to reduce song complexity could be achieved by repeating individual syllables. In this context here we examined the importance of males repeating syllables in male-male interactions. We hypothesis that repeating syllables signals a males general fighting ability, aggressive status or willingness to attack. In a playback experiment we investigated the behavioral response of unmated, territorial Eurasian reed warbler (Acrocephalus scirpaceus) males towards two simultaneously singing intruders whereby the song of the two simulated intruders differs in the degree of syllable repetitions. The response of the territory owner was determined by using several behavioral parameters. Our results revealed that males approached faster and stayed significantly longer near the song with few syllable repetitions. However, the proportion of males approaching the song with high or low syllable repetitions first, as well as the minimal distance to which males approach to the two song types did not differ as well. Thus, the weaker response towards the high repetitive song playback suggests territorial males to be more intimidated by the aggressive nature of that song type. [ABSTRACT FROM AUTHOR]

Cooperative breeding occurs when helpers provide alloparental care to the offspring of a breeding pair. One hypothesis of why helping occurs is that helpers gain valuable skills that may increase their own future reproductive success. However, research typically focuses on the effect of helping on short-term measures of reproductive success. Fewer studies have considered how helping affects long-term fitness measures. Here, we analyze how helping experience affects key breeding and fitness-related parameters in the Seychelles warbler (Acrocephalus sechellensis). Importantly, we control for females that have cobred (reproduced as a subordinate by laying an egg within a territory in which they are not a dominant breeder), as they already have experience with direct reproduction. Helping experience had no significant association with any of the metrics considered, except that helpers had an older age at first dominance. Accounting for helping experience, females that had cobred produced more adult offspring (≥1 year) after acquiring dominance and had a higher lifetime reproductive success (LRS) than females that had never cobred. Our results suggest that, in the Seychelles warbler, helping experience alone does not increase the fitness of helpers in any of the metrics considered, and highlights the importance of separating the effects of helping from cobreeding. Our findings also emphasize the importance of analyzing the effect of helping at various life-history stages, as higher short-term fitness may not translate to an overall increase in LRS. [ABSTRACT FROM AUTHOR]

Egg recognition and rejection are the most common and effective anti‐parasitic strategies against avian brood parasitism in terms of maintaining stability over time and plasticity in response to environmental cues. Conversely, parasites have evolved multiple counter‐adaptations to the anti‐parasitic defenses of hosts. Among them, the crypsis hypothesis suggests that eggs that appear more cryptic in color and are closely matched to the environment are helping to counter the egg recognition strategy of the host. In this study, we investigated whether the egg recognition ability of Oriental reed warblers (Acrocephalus orientalis), a common host of common cuckoos (Cuculus canorus), changed during different reproductive stages by using model egg experiments. The effect of the crypsis hypothesis on the egg recognition ability of the hosts was also investigated by controlling the color contrast between the inside of the experimental nests and the model eggs. The results showed that the Oriental reed warbler retained strong egg recognition abilities, which were similar to the incubation stage (GLMMs: F1,27 = 0.424, p =.521), even after entering the nestling stage and preferentially rejected model eggs with distinct contrasting colors (binomial test: Fisher's exact, p =.016). These results are consistent with the crypsis hypothesis. The present study suggests that the host retains a strong egg recognition ability even during the nestling stage and that cryptic‐colored eggs that are closely matched with the breeding nest environment help counter the host's egg recognition abilities and increase the chances of successful parasitism by cuckoos. However, the effectiveness of cryptic egg may be weaker than mimic egg in countering egg recognition and rejection by hosts with open‐cup nests. [ABSTRACT FROM AUTHOR]

In cooperatively breeding species, sexually mature individuals may delay natal dispersal and become subordinates, helping a dominant pair raise offspring. To understand how cooperative breeding evolved, it is important to determine the mechanisms leading to delayed dispersal. Adult sex ratio (ASR) variation may affect dispersal by limiting breeding vacancies available to the more abundant sex, and cooperative breeders often have a more biased ASR than noncooperative breeders. However, no studies of cooperative breeders have related ASR at both the local and population level with dispersal. Using the long-term Seychelles warbler, Acrocephalus sechellensis , data set, we tested the influence of population-wide and local ASR, and density, on natal dispersal of yearlings. Our ASR - density hypothesis predicts that the probability of natal dispersal is lower when the ASR is biased towards the sex of the focal individual, but only when the population density is high. Dispersal was associated with population density and population-wide ASR in males, but not in females; males were more likely to delay dispersal when ASR was male biased and density was high. Our findings illustrate a complex association between demographic factors and cooperative breeding and suggest that individuals alter their dispersal behaviour in response to the demographic composition of the population. • Natal dispersal is associated with ASR in a facultative cooperative breeder. • Male but not female yearlings disperse in response to population ASR and density. • Population-wide rather than local demographic composition predicted male dispersal. • Our study links demographic factors with behaviour that drives cooperative breeding. [ABSTRACT FROM AUTHOR]

Geographic distribution models of environmentally stable isotopes (the so‐called "isoscapes") are widely employed in animal ecology, and wildlife forensics and conservation. However, the application of isoscapes is limited to elements and regions for which the spatial patterns have been estimated. Here, we focused on the ubiquitous yet less commonly used stable sulfur isotopes (δ34S). To predict the European δ34S isoscape, we used 242 feather samples from Eurasian Reed Warbler (Acrocephalus scirpaceus) formed at 69 European wetland sites. We quantified the relationships between sample δ34S and environmental covariates using a random forest regression model and applied the model to predict the geographic distribution of δ34S. We also quantified within‐site variation in δ34S and complementarity with other isotopes on both individual and isoscape levels. The predicted feather δ34S isoscape shows only slight differences between the central and southern parts of Europe while the coastal regions were most enriched in 34S. The most important covariates of δ34S were distance to coastline, surface elevation, and atmospheric concentrations of SO2 gases. The absence of a systematic spatial pattern impedes the application of the δ34S isoscape, but high complementarity with other isoscapes advocates the combination of multiple isoscapes to increase the precision of animal tracing. Feather δ34S compositions showed considerable within‐site variation with highest values in inland parts of Europe, likely attributed to wetland anaerobic conditions and redox sensitivity of sulfur. The complex European geography and topography as well as using δ34S samples from wetlands may contribute to the absence of a systematic spatial gradient of δ34S values in Europe. We thus encourage future studies to focus on the geographic distribution of δ34S using tissues from diverse taxa collected in various habitats over large land masses in the world (i.e., Africa, South America, or East Asia). [ABSTRACT FROM AUTHOR]

Stable isotope analysis provides valuable insights into the ecology of long-distance migratory birds during periods spent away from a specific study site. In a previous study, Swedish great reed warblers (Acrocephalus arundinaceus) infected with haemosporidian parasites differed in feather isotope ratios compared to non-infected birds, suggesting that infected and non-infected birds spent the non-breeding season in different locations or habitats. Here, we use a novel dataset comprising geolocator data, isotopes, and haemosporidian infection status of 92 individuals from four Eurasian populations to investigate whether parasite transmission varies with geography or habitats. We found that the probability of harbouring Plasmodium and Leucocytozoon parasites was higher in birds moulting in the eastern region of the non-breeding grounds. However, no geographic pattern occurred for Haemoproteus infections or overall infection status. In contrast to the previous study, we did not find any relationship between feather isotope ratios and overall haemosporidian infection for the entire current dataset. Plasmodium-infected birds had lower feather δ15N values indicating that they occupied more mesic habitats. Leucocytozoon-infected birds had higher feather δ34S values suggesting more coastal sites or wetlands with anoxic sulphate reduction. As the composition and prevalence of haemosporidian parasites differed between the old and the current dataset, we suggest that the differences might be a consequence of temporal dynamics of haemosporidian parasites. Our results emphasize the importance of replicating studies conducted on a single population over a restricted time period, as the patterns can become more complex for data from wider geographical areas and different time periods. [ABSTRACT FROM AUTHOR]

Double brooding, the laying of a second clutch after successfully fledging young from a first nest in a season, is a common reproductive strategy among short-lived birds to increase annual breeding success. Nevertheless, there is widespread intra- and interspecific variation in the probability of producing a second clutch. Given that the frequency of double brooding could affect population growth rate, knowing what factors contribute to this phenomenon is also important in the conservation management of threatened facultative double-brooded species. Here, we examine the frequency of double brooding and the factors affecting the probability of this reproductive strategy in a population of the Great Reed Warbler, Acrocephalus arundinaceus, in south-western Slovakia. Results of a 15-year study (2008–2022) revealed low overall rate of double brooding in the Great Reed Warbler (5.6% per year, 0–15.4%). The length of breeding season, timing of the first clutch laying date and the size of the first broods were key factors influencing the female's decision to initiate a second clutch. On the other hand, successful brood parasitism did not affect second clutch initiation, which contrasts with our prediction. Given that only monogamous or primary females initiated a second clutch after successfully rearing a first one, we assume that producing two broods within the same season may be an alternative strategy for monogamous males to increase their annual reproductive output in this facultatively polygynous species. Therefore, due to relatively high rate of polygyny, we probably cannot expect higher rate of double broodings in the Great Reed Warbler in the future either. [ABSTRACT FROM AUTHOR]

Byzantine kratēmata, widely known as the terrirem, as part of other, broader musical works, date approximately back to the eleventh–twelfth century. A small group of four kratēmata are named after birds (Aēdhon – Luscinia megarhynchos, Potamis – Acrocephalus, Anyfantis and Papadopoula – Parus major). It is reasonable to assume that the singing of the respective birds inspired composers to set these kratēmata to music. Studying the related compositions, as they have been documented in the written tradition of the Byzantine and the post-Byzantine manuscripts until their transcription from the pre-1814 old stenographic method notation, we report certain observations that reinforce the initial hypothesis, as well as some parallel remarks about the phenomenon of creation, establishment, and spreading of this form. [ABSTRACT FROM AUTHOR]

In the sexual selection framework, nuptial gifts are materials a donor provides to a receiver that can increase the donor's fitness. In specific cases, sharing crucial information may be a nonmaterial nuptial gift. To investigate this hypothesis, we focused on the common cuckoo, Cuculus canorus , an obligate avian brood parasite whose reproduction costs of females are mainly related to finding host nests needed to lay their eggs. Nest searching is assumed to be conducted only by females. We hypothesized that males could contribute by transferring information on nest locations to females as a nonmaterial nuptial gift. Here, we show the results of a first step in this direction, in which we identified any behaviour potentially conveying information on nest abundance in the surrounding area, that is, behaviours whose frequency varied with host nest density. We conducted our investigation in a marshland area within the Po Plain (Italy), where we recorded both visual displays of cuckoos at perching sites, by using camera traps, and nest abundance of two of the most parasitized cuckoo host species, the reed warbler, Acrocephalus scirpaceus , and great reed warbler, Acrocephalus arundinaceus , by systematic nest monitoring. We found that male cuckoos adopted a certain posture, wing drooping, and tended to keep their tails up more frequently in areas with the highest versus lowest host nest densities. This is consistent with these behaviours acting as potential signals codifying information on nest abundance in the area. We finally discuss the implications of our findings for the mating choices of female cuckoos and the study directions warranted to reveal whether these displays and information transfer may be included as new elements of the sexual selection framework. • Cuckoo males may help females in nest searching by sharing information on nests. • We identified some behaviours preferentially performed in areas rich in host nests. • Under specific circumstances, information may act as a nuptial gift. • Further studies are needed to assess if these behaviours affect female mate choice. [ABSTRACT FROM AUTHOR]

Breeding habitat loss and depletion of genetic diversity can have critically negative impacts on species, and especially so for habitat specialists. The Aquatic Warbler Acrocephalus paludicola is a threatened European songbird that breeds in fens, which have been lost and fragmented over centuries. We used microsatellite loci to perform a spatial and longitudinal comparison, comparing samples collected recently (contemporary) with those obtained about two decades earlier (historical) from c. 25% of the breeding range (Biebrza and Polesie) of the Aquatic Warbler. With these data we explored changes in genetic diversity, expansions and reductions of population size, population structure, and gene flow. Allelic richness, expected heterozygosity, the number of effective and private alleles, and effective population size (NE ≈ 200) were low and comparable across time and space. We detected a genetic bottleneck in contemporary Biebrza, and a less certain bottleneck in both historical and contemporary Polesie. Across space, Biebrza and Polesie were not genetically differentiated in either period. All the historical samples clustered together, but in the contemporary samples a small part of Polesie clustered separately (FST = 0.011). Across time, Biebrza and Polesie showed low but significant differentiation (FST = 0.026–0.064), and historical and contemporary groups clustered apart. A principal coordinate analysis on genetic distance detected three groups, which spanned sampling locations. In the temporal comparison, the contemporary group and contemporary Biebrza had elevated mean within‐group pairwise relatedness. We did not recover signals for sex‐biased dispersal, asymmetric gene flow or isolation‐by‐distance using the molecular data. Our results suggest that the studied populations show: (1) impoverished genetic diversity, (2) a change in allele frequencies over the two decades studied and (3) high gene flow between distant breeding sites, implying high resilience to habitat fragmentation that should facilitate the success of recolonising restored habitat patches by Aquatic Warblers. [ABSTRACT FROM AUTHOR]

In recent years, the breeding populations of many migratory songbird species have declined in the Carpathian Basin. However, there may be significant differences between different geographical regions, as most species have a much higher chance of successful breeding in protected areas. This is also the case for the Moustached Warbler, one of the most habitat-specialist passerine. It colonises only perennial, unharvested reedbeds, therefore its conservation management is essential. We studied the population changes of this species between 2001 and 2022 at Lake Kolon in Izsák, based on bird ringing data from 10–24 July. Data of 12,817 ringed and 5,075 recaptured birds were used in the analyses. The annual capture rate decreased significantly during the study period. The proportion of juveniles was higher at higher water levels during the whole breeding season. In contrast, when looking at winter and first and second broods separately, water level had no effect on the juvenile/adult ratio. This is because the birds compensate for unsuccessful first broods by increasing the proportion of second and replacement broods. If the first broods are successful, the ratio of second and replacement broods will be lower. As reed management is practically non-existent in this area, the perennial reedbeds provide suitable nesting conditions for the species. Changes in the wintering sites may be responsible for the declining trend. Protection of the area is of particular importance for the conservation of the species. [ABSTRACT FROM AUTHOR]

Reports of physical abnormalities in wild bird populations are rare and often anecdotal, whereas reliable estimates of their frequency are important to understand the strength of selection against them. In 2005-2022, we studied various aspects of breeding biology of Eurasian reed warblers and monitored a total of 1194 nests. In July 2022, we observed a deformed nestling of this species in a brood of three young. The nestling displayed a soft distended lump around the cervical area. After further inspection, we concluded that the nestling suffered from subcutaneous emphysema, which resulted in its death on the following day. The nestling body was collected and examined for the presence of injuries, parasitic nematodes and bacteria. We discuss possible factors that might have caused the nestling's emphysema and conclude that Clostridium bacteria found in the nestling tissues were the most likely cause of its symptoms and death. This was the only case of subcutaneous emphysema recorded in our population among 1995 nestlings of the same age (8th day after hatching), making up 0.05% of all. [ABSTRACT FROM AUTHOR]

Background: Recombination reshuffles alleles at linked loci, allowing genes to evolve independently and consequently enhancing the efficiency of selection. This makes quantifying recombination along chromosomes an important goal for understanding how selection and drift are acting on genes and chromosomes. Results: We present RecView, an interactive R application and its homonymous R package, to facilitate locating recombination positions along chromosomes or scaffolds using whole-genome genotype data of a three-generation pedigree. RecView analyses and plots the grandparent-of-origin of all informative alleles along each chromosome of the offspring in the pedigree, and infers recombination positions with either of two built-in algorithms: one based on change in the proportion of the alleles with specific grandparent-of-origin, and one on the degree of continuity of alleles with the same grandparent-of-origin. RecView handles multiple offspring and chromosomes simultaneously, and all putative recombination positions are reported in base pairs together with an estimated precision based on the local density of informative alleles. We demonstrate RecView using genotype data of a passerine bird with an available reference genome, the great reed warbler (Acrocephalus arundinaceus), and show that recombination events can be located to specific positions. Conclusions: RecView is an easy-to-use and highly effective application for locating recombination positions with high precision. RecView is available on GitHub (https://github.com/HKyleZhang/RecView.git). [ABSTRACT FROM AUTHOR]

Germline mutations are the ultimate source of genetic variation and the raw material for organismal evolution. Despite their significance, the frequency and genomic locations of mutations, as well as potential sex bias, are yet to be widely investigated in most species. To address these gaps, we conducted whole-genome sequencing of 12 great reed warblers (Acrocephalus arundinaceus) in a pedigree spanning 3 generations to identify single-nucleotide de novo mutations (DNMs) and estimate the germline mutation rate. We detected 82 DNMs within the pedigree, primarily enriched at CpG sites but otherwise randomly located along the chromosomes. Furthermore, we observed a pronounced sex bias in DNM occurrence, with male warblers exhibiting three times more mutations than females. After correction for false negatives and adjusting for callable sites, we obtained a mutation rate of 7.16 × 10−9 mutations per site per generation (m/s/g) for the autosomes and 5.10 × 10−9 m/s/g for the Z chromosome. To demonstrate the utility of species-specific mutation rates, we applied our autosomal mutation rate in models reconstructing the demographic history of the great reed warbler. We uncovered signs of drastic population size reductions predating the last glacial period (LGP) and reduced gene flow between western and eastern populations during the LGP. In conclusion, our results provide one of the few direct estimates of the mutation rate in wild songbirds and evidence for male-driven mutations in accordance with theoretical expectations. [ABSTRACT FROM AUTHOR]

Sexual conflict has long been perceived as a solid background for the evolution of parental care. Recent studies, however, highlight the importance of cooperation between the parents, especially in socially monogamous systems. Here, we examined parental performance of a small monogamous passerine with bi-parental care, the Eurasian Reed Warbler (Acrocephalus scirpaceus, RW), looking at the issue from the perspective of parents' cooperation. Using accurate and non-invasive video data on parent chick provisioning from 78 nests varying in brood size, we found some evidence of parents cooperation: both parents similarly adjusted their feeding rate to brood size, and the higher was their both contribution, the better was chicks condition (expressed by defecation rate). However, contrary to our expectations (based on premises from similar studies on other bird species) we did not find evidence for frequent and active synchronisation of nest visits. Importantly, we found a negative relationship between synchronisation level and chick body condition, suggesting that synchronisation may actually not be that beneficial in the study system. The results are surprising and highlight the importance of studying various species to understand mechanisms behind cooperation of partners in the bi-parental care system. Significance statement: Biparental care has long been viewed in the context of conflict between the breeding partners, and only recently they are considered cooperating agents caring together for the common offspring. Nevertheless, studies applying such a perspective are still scarce and there is a pressing need to test different species. Using video data on chick provisioning by Reed Warbler parents, we found evidence of partner cooperation: both parents adjusted their feeding rate to the number of nestlings, and the higher was their joint contribution, the better was offspring condition. Parents did not synchronise their nest visits more compared to randomly generated visits, but we found that synchronisation level negatively affected chick condition. Our results highlight the need to consider various species to fully understand mechanisms behind cooperation of breeding partners. [ABSTRACT FROM AUTHOR]

The survival of migratory passerines depends considerably on conditions experienced on their non-breeding grounds. However, these critical non-breeding sites are generally poorly known, especially for species and populations using the eastern Afro-Palearctic flyway. To fill this gap, we measured hydrogen stable isotopes in winter-grown feathers (δ2Hf) of five long-distance migratory passerines (Eurasian Blackcap, Eastern Olivaceous Warbler, Eurasian Reed Warbler, Olive-tree Warbler, and Barred Warbler) collected during spring migration at a stopover site in Israel, a major migratory bottleneck in the Afro-Palearctic Flyway. We determined non-breeding origins of these species, for the entire migrating population and for early- and late-arriving individuals separately. We used a probabilistic model based on feather isotopes and isotopic distribution of precipitation δ2H (δ2Hp) in Africa, as well as range maps derived from species distribution models and expert opinion. While our results suggested that Reed Warbler and Olive-tree Warbler occupy most of their known range during the non-breeding season, Blackcaps migrating through Jerusalem, Israel, likely spent the non-breeding season specifically in Ethiopia and near areas, and Eastern Olivaceous Warbler concentrated in two regions in eastern tropical and central Africa. Barred Warblers' non-breeding grounds were estimated in Kenya, but the species distribution model approach suggested additional regions. Our results further suggested that early- and late-arriving Reed Warblers spent the non-breeding season in separate areas, whereas early- and late-arriving Blackcaps migrated to the same area. Given the rapid decline in many migratory species, our results are important for a more accurate evaluation of the conditions experienced during the non-breeding season and our study is a template for refining migratory connectivity estimates for species using this important flyway. [ABSTRACT FROM AUTHOR]

In 2022 two new colonies of Pallid Swift Apus pallidus were found in Brig VS and Geneva. For the first time a Red Kite Milvus milvus bred in the canton Ticino. The populations of Greylag Goose Anser anser (124 broods), White Stork Ciconia ciconia (887 broods), Great Cormorant Phalacrocorax carbo (3438 broods), Bearded Vulture Gypaetus barbatus (26 broods) und Short-toed Snake-eagle Circaetus gallicus (11 broods) have increased again in 2022. High breeding numbers were registered for Spotted Crake Porzana porzana (25 territories), Little Crake Zapornia parva (8 territories) und Zitting Cisticola Cisticola juncidis (12 territories), a low number for Corncrake Crex crex (16 singing males). Rare breeding records or reports of territories were found for: Common Eider Somateria mollissima (2 broods), Common Goldeneye Bucephala clangula (1 brood), Ferruginous Duck Aythya nyroca (1 brood), Black-necked Grebe Podiceps nigricollis (2 broods), Baillon's Crake Zapornia pusilla (1 territory), Eurasian Dotterel Eudromias morinellus (2 breeding pairs), Common Snipe Gallinago gallinago (1 territory), Mediterranean Gull Larus melanocephalus (1 brood), Mew Gull L. canus (1 breeding pair), Western Marsh-harrier Circus aeruginosus (3 broods), Moustached Warbler Acrocephalus melanopogon (1 territory), Subalpine Warbler Sylvia cantillans (1 brood), Spectacled Warbler S. conspicillata (1 territory), Tawny Pipit Anthus campestris (5 territories) and Citrine Wagtail Motacilla citreola (1 territory). An Arctic Tern Sterna paradisaea bred again together with a Common Tern S. hirundo. No territories were found for Grey Partridge Perdix perdix and Ortolan Bunting Emberiza hortulana. [ABSTRACT FROM AUTHOR]

Many studies have found that if hosts observe a brood parasite at their nest, they use it as a cue to reject parasitic eggs. However, most previous work has simulated brood parasitic events by exposing a stuffed parasite near a host's nest. Responses to the presence of a real parasite have not yet been adequately studied under natural conditions. We therefore investigated whether great reed warblers (Acrocephalus arundinaceus) are more likely to reject a parasitic egg if they see a parasitizing common cuckoo (Cuculus canorus) at their nest than if the parasite approaches the host nest unnoticed. Using video recordings of 70 nests, we showed that spotting a cuckoo at the nest did not increase the rejection rate of parasitic eggs, even if hosts saw the cuckoo repeatedly. Hosts instead used the level of mimicry in the background color for cuckoo egg rejection. Since not every visit by the cuckoo leads to parasitism, seeing the brood parasite may not be a reliable enough cue for the host. Therefore, our results suggest that the sight of a cuckoo at the nest may not have as severe consequences for it as previously thought. [ABSTRACT FROM AUTHOR]

Birds have evolved morphological, physiological and behavioural adaptations, encoded in their migratory programs, to enable successful migration. Sometimes, even closely related species, such as the Eurasian reed warbler and the sedge warbler, may adopt different migration strategies to reach their wintering grounds in sub-Saharan Africa. To study them in detail, we aimed to compare the temporal variations of activity patterns and fuelling of lab-held warblers caught in southern Sweden during autumn migration and compared the results with respect to known differences in their migration strategies. In order to investigate if the activity and fuelling were controlled by magnetic information, two groups of birds per species were experimentally subjected to magnetic fields anticipated during their migration via the Mediterranean and at the winter destinations, and control experiments were performed in the local magnetic field. Both species expressed a peak of nocturnal activity just after sunset and increased activity before sunrise. Reed warblers were strictly active during the night, whereas sedge warblers also showed increased morning activity possibly associated with intense foraging during stopover and longer migratory flights extending into the day when passing ecological barriers. There was no difference in overall activity between the two species but a change of active intervals during the experimental period with reed warblers increasing and sedge warblers decreasing activity over time, probably reflecting similar anticipated migration distances but differences in migratory strategies. The simulation of magnetic parameters influenced the activity and fuelling in reed warblers, but not in sedge warblers. These results support inherited differences in migratory strategies observed in the wild and suggest species-specific adaptations to magnetic field information regulating migration. Significance statement: Migratory birds often cover thousands of kilometres between their breeding and wintering sites. To successfully reach the destination, a bird may adopt a unique migration strategy including accumulation of fuel reserves and changes of diel activity pattern. Field observations have revealed how populations of birds perform their migrations; however, detailed monitoring of activity and fuelling over time for individual birds in a controlled setting is only possible in the laboratory. By using continuous video recording and automatic computer vision behavioural analysis, we quantified migratory activity patterns of two related species of warblers. We show that Eurasian reed warblers were strictly active during night, whereas sedge warblers also showed increased morning activity reflecting their migratory strategies observed in the wild. By simulating the magnetic field of sites along the migration route and wintering grounds, we found species-specific adaptations to magnetic field information. [ABSTRACT FROM AUTHOR]

Long-distance migratory animals such as birds and bats have evolved to withstand selection imposed by pathogens across the globe, and pathogen richness is known to be particularly high in tropical regions. Immune genes, so-called Major Histocompatibility Complex (MHC) genes, are highly duplicated in songbirds compared to other vertebrates, and this high MHC diversity has been hypothesised to result in a unique adaptive immunity. To understand the rationale behind the evolution of the high MHC genetic diversity in songbirds, we determined the structural properties of an MHC class I protein, Acar3, from a long-distance migratory songbird, the great reed warbler Acrocephalus arundinaceus (in short: Acar). The structure of Acar3 was studied in complex with pathogen-derived antigens and shows an overall antigen presentation similar to human MHC class I. However, the peptides bound to Acar3 display an unusual conformation: Whereas the N-terminal ends of the peptides display enhanced flexibility, the conformation of their C-terminal halves is rather static. This uncommon peptide-binding mode in Acar3 is facilitated by a central Arg residue within the peptide-binding groove that fixes the backbone of the peptide at its central position, and potentially permits successful interactions between MHC class I and innate immune receptors. Our study highlights the importance of investigating the immune system of wild animals, such as birds and bats, to uncover unique immune mechanisms which may neither exist in humans nor in model organisms. [ABSTRACT FROM AUTHOR]

Climatic conditions affect animals but range‐wide impacts at the population level remain largely unknown, especially in migratory species. However, studying climate–population relationships is still challenging in small migrants due to a lack of efficient and cost‐effective geographic tracking method.Spatial distribution patterns of environmental stable isotopes (so called 'isoscapes') generally overcome these limitations but none of the currently available isoscapes provide a substantial longitudinal gradient in species‐rich sub‐Saharan Africa. In this region, sulphur (δ34S) has not been sufficiently explored on a larger scale.We developed a δ34S isoscape to trace animal origins in sub‐Saharan Africa by coupling known‐origin samples from tracked migratory birds with continental remotely sensed environmental data building on environment–δ34S relationships using a flexible machine learning technique. Furthermore, we link population‐specific nonbreeding grounds with interannual climatic variation that might translate to breeding population trends.The predicted δ34S isotopic map featured east–west and coast‐to‐inland isotopic gradients and was applied to predict nonbreeding grounds of three breeding populations of Eurasian Reed Warblers Acrocephalus scirpaceus with two distinct migratory phenotypes. Breeding populations as well as migratory phenotypes exhibited large‐scale segregation within the African nonbreeding range. These regions also differed substantially in the interannual climatic variation, with higher interannual variability in the eastern part of the range during 2001–2012. Over the same period, the eastern European breeding population seemed to have experienced a more steep decline in population size.The link between migratory patterns and large‐scale climatic variability appears important to better understand population trajectories in many declining migratory animals. We believe animal tracing using sulphur isotopes will facilitate these efforts and offers manifold ecological and forensic applications in the biodiversity hotspot of sub‐Saharan Africa. [ABSTRACT FROM AUTHOR]

Long-read sequencing offers a great improvement in the assembly of complex genomic regions, such as the major histocompatibility complex (MHC) region, which can contain both tandemly duplicated MHC genes (paralogs) and high repeat content. The MHC genes have expanded in passerine birds, resulting in numerous MHC paralogs, with relatively high sequence similarity, making the assembly of the MHC region challenging even with long-read sequencing. In addition, MHC genes show rather high sequence divergence between alleles, making diploid-aware assemblers incorrectly classify haplotypes from the same locus as sequences originating from different genomic regions. Consequently, the number of MHC paralogs can easily be over- or underestimated in long-read assemblies. We therefore set out to verify the MHC diversity in an original and a haplotype-purged long-read assembly of one great reed warbler Acrocephalus arundinaceus individual (the focal individual) by using Illumina MiSeq amplicon sequencing. Single exons, representingMHCclass I (MHC-I) and class IIB (MHC-IIB) alleles, were sequenced in the focal individual and mapped to the annotated MHC alleles in the original long-read genome assembly. Eighty-four percent of the annotated MHC-I alleles in the original long-read genome assembly were detected using 55% of the amplicon alleles and likewise, 78% of the annotated MHCIIB alleles were detected using 61% of the amplicon alleles, indicating an incomplete annotation of MHC genes. In the haploid genome assembly, each MHC-IIB gene should be represented by one allele. The parental origin of the MHC-IIB amplicon alleles in the focal individual was determined by sequencing MHC-IIB in its parents. Two of five larger scaffolds, containing 6-19 MHC-IIB paralogs, had a maternal and paternal origin, respectively, as well as a high nucleotide similarity, which suggests that these scaffolds had been incorrectly assigned as belonging to different loci in the genome rather than as alternate haplotypes of the same locus. Therefore, the number of MHCIIB paralogs was overestimated in the haploid genome assembly. Based on our findings we propose amplicon sequencing as a suitable complement to long-read sequencing for independent validation of the number of paralogs in general and for haplotype inference in multigene families in particular. [ABSTRACT FROM AUTHOR]

Interactions between avian brood parasites, such as common cuckoos (Cuculus canorus), and their hosts are one of the best‐studied examples of the coevolutionary arms race. Different stages of this arms race can be seen in different races of common cuckoos and their hosts across their range. However, little is known whether selected populations of two closely related but geographically distant species with probably different coevolutionary histories with the common cuckoo are also at different stages of the arms race. In this study, we tested this prediction experimentally using the same non‐mimetic model eggs and three‐dimensional (3D) printed models of the gray adult common cuckoo (Cuculus canorus). We examined egg recognition and egg rejection and aggression against the common cuckoo in the great reed warbler (Acrocephalus arundinaceus) and Oriental reed warbler (Acrocephalus orientalis), in Slovakia of Europe and northeast China of Asia. The results showed that the great reed warbler exhibited stronger responses to experimental model eggs and 3D models of the common cuckoo than the Oriental reed warbler. We conclude that both the great reed warbler and Oriental reed warbler have well‐developed antiparasitic behaviors against common cuckoos in the studied populations, but with different levels of defense intensity, which may be due to local differences in parasitic pressure and the risk of parasitism. This provides an opportunity to study coevolutionary processes between the brood parasite and its hosts together in both species at large geographical scales. [ABSTRACT FROM AUTHOR]

The cost–benefit approach to nest defence behaviour is based on an assumption that parents are able to distract potential predators away from their nest. However, this assumption has received little support from direct observations as predator-prey encounters near nests are rarely recorded, especially in small passerines. Here, we describe two observations of little bitterns appearing near nests of Eurasian reed warblers containing nestlings and eggs, respectively. In both cases parental birds showed anti-predatory behaviour, which was much more vigorous at the nestling stage than at the egg stage. During both observations, the heron finally flew away and did not attack the nest content, indicating that nest defence behaviour of small passerines may be effective. [ABSTRACT FROM AUTHOR]

This is the 85th annual report of the British Trust for Ornithology's Ringing Scheme, incorporating the report of the Nest Record Scheme and covering work carried out and data processed in 2021. In 2021, 105 Constant Effort Sites submitted data for the year. Long-term (1984–2020) declines in abundance were observed for five migrant, one partial migrant and five resident species, while long-term increases in abundance were recorded for two short-distance migrants and seven resident species. Ten species are exhibiting significant long-term declines in productivity, while only Chaffinch Fringilla coelebs shows a significant long-term increase. Long-term trends in survival indicate increases for 12 species and declines for seven. Short-term trends, which compare the current year to the five-year mean for 2016–20, show that the abundance of seven species increased significantly in 2021, with one species, Treecreeper Certhia familiaris, being recorded in higher numbers than in any previous year of CES monitoring. Significant decreases in abundance were recorded for four species. Productivity decreased significantly for seven migrant and 11 resident species in 2021, with six species recording their lowest breeding success since CES monitoring began; no species recorded a significant short-term increase. Significant changes in survival rate were observed for two species in 2021 compared to the five-year mean, with Song Thrush Turdus philomelos increasing and Chaffinch both declining and recording its lowest survival rate ever. The Garden CES trial continued in 2021, with 60 sites submitting data. The new winter ringing project also continued in 2021, with submissions received from 126 sites. The number of Retrapping Adults for Survival projects that were able to run and submit data in 2021 was 192, with data from one more project submitted too late to be included in this report and another four active projects unable to operate. In total, 60 species were monitored, with Starling Sturnus vulgaris (21 projects), House Sparrow Passer domesticus (20 projects), Pied Flycatcher Ficedula hypoleuca (19 projects), Reed Warbler Acrocephalus scirpaceus (nine projects) and Sand Martin Riparia riparia (nine projects) the species most studied. A total of 900 131 birds were ringed during the year, comprising 146 458 nestlings, 438 342 first-year birds, 291 127 adults (birds in their second calendar year or older) and 24 204 birds whose age could not be determined. In addition, there were 210 147 recaptures of ringed birds at or near the ringing site. In total, 42 328 recoveries (birds found dead, recaptured or resighted at least 5 km from the place of ringing) of BTO-ringed birds were reported in 2021. The Appendix highlights a selection of recoveries that have extended our knowledge of movements, as well as longevity records established during the year. A total of 41 096 NRS submissions were received in 2021. Mean laying dates for 2021 were significantly later than the average for 13 species and only one species significantly advanced its laying date. Five species displayed a significant change in fledglings per breeding attempt, with two recording increased productivity and three reduced productivity. Permits or licences to disturb breeding birds on Schedule 1 of the Wildlife and Countryside Act 1981 (as amended) were prepared and issued to 602 ringers and nest recorders in 2021. During 2021, 2588 marking endorsements, 868 sampling endorsements and 214 trapping endorsements were issued in the UK and overseas. [ABSTRACT FROM AUTHOR]

The Aquatic Warbler Acrocephalus paludicola is one of the rarest European passerines and is characterised by promiscuity, lack of pair-bonds and female-only parental care. This makes the species an important model for studying the function of avian courtship song. The song of the Aquatic Warbler consists of whistle and rattle phrases produced as discontinuous A-, B- and C-songs, which are built by a single rattle, a rattle and a whistle, and more than two phrases of both kinds, respectively. The A- and B-songs are thought to be aggressive signals in male-male interactions, while C-songs are thought to be important for female choice. Here, we analysed recordings of 40 individually marked males, and determined the phrase repertoire. The enumerated repertoire (males recorded for ≥ 10 min) ranged from 16 to 158 (mean 99), however, it did not capture the complete phrase repertoires. We then used models from species diversity ecology to estimate the actual phrase repertoire size, which ranged between 18 and 300 phrases (mean 155). The estimated repertoire was predicted by the number of C-songs. The rattle repertoire was larger than the whistle repertoire, and both positively correlated with the number of C-songs. Our study indicates that male Aquatic Warblers have highly complex phrase repertoires that vary widely in size. Their courtship song is flexible and efficient, enabling relative song complexity to be demonstrated in a short sample, thus facilitating both female attraction through the quick presentation of large phrase repertoires and rival deterrence through the production of many short and simple A- and B-songs. [ABSTRACT FROM AUTHOR]

Furthermore, the body conditions of both migrant and resident bird species were positively linked to landscape connectivity, while the influence of forest patch area was only significant for resident bird species. In recent years, there have been great advances in both the use of new technologies and analytical techniques for studying bird ecology and in the examination of the evolutionary origins of bird diversity and bird distributions. Species distribution modelling has revolutionised the way in which we quantify and visualise species habitat preferences at appropriate scales, identify priority areas for bird conservation, and predict how these attributes may change under different climate and land-use scenarios. [Extracted from the article]

We studied the trematode fauna in land birds from the Republic of Mordovia (European Russia) in 2018–2022. In total, we identified 16 digenean species in 45 species of birds from the orders Passeriformes, Piciformes, Caprimulgiformes and Falconiformes. The trematodes Phaneropsolus micrococcus and Morishitum polonicum were recorded for the first time in the birds' parasite fauna of Russia. We obtained the first data on helminths in Hippolais icterina and Ficedula albicollis from Russia and in Coccothraustes coccothraustes from the Middle Volga region. New host records resulting from our study include Brachylaima mesostoma from Coccothraustes coccothraustes; Urogonimus macrostomus from Sylvia atricapilla, Ficedula albicollis, Ficedula hypoleuca and Acrocephalus palustris; Plagiorchis maculosus from Ficedula albicollis and Hippolais icterina; and Lyperosomum alaudae from Ficedula hypoleuca. The common parasite of rallid birds Leucochloridium holostomum is recorded for the first time from Turdus merula in Russia. Taking into account the newly obtained data, we carried out a review of trematodes in land birds of the Middle Volga region, of which the Republic of Mordovia is a part. Currently, the list of land bird digeneans in the Middle Volga region includes 56 species. Among all the studied land birds, members of the order Passeriformes have the richest trematode fauna (33 species). The diversity of trematodes found in passerines is due to the large number of both individuals and species studied and the variety of habitats and diet preferences of these land birds. Most of the identified trematode faunas (47 species) are obligate parasites of land birds. Nine species parasitize land birds accidentally and/or facultatively. In the Middle Volga area, the fauna of trematodes is the most diverse in land birds of the Nizhny Novgorod region, where 31 species are revealed. Fewer species of trematodes are identified in birds from the Bashkortostan (20), Mordovia (17) and Samara regions (15). For the birds of Chuvashia and Tatarstan, only eight and one species of trematodes are known, respectively. Six trematode species, found in land birds, have veterinary and medical significance as potential pathogens of dangerous helminthiases. [ABSTRACT FROM AUTHOR]

Despite efforts on ecosystem restoration and management, biodiversity loss remains one of the major environmental concerns of our time. Beyond the focus on threatened species, animals that indicate regional biodiversity hotspots and population trends, such as brood parasites, should also be targeted by conservation actions. We studied how reed habitat quality and management influence brood parasitism rate and offspring survival in Common Cuckoos Cuculus canorus parasitizing nests of Great Reed Warblers Acrocephalus arundinaceus in six reed habitats in an intensive agricultural landscape. Data collected from 45 sites over 13 years showed that the brood parasitism rate was highest on large canals and was positively influenced by the availability of potential perches (Cuckoo vantage points) and the height where host nests were built. Cuckoo chick survival decreased with water depth and was not affected by other factors. Our results suggest that the habitat‐dependent detectability of host nests was central in brood parasitism rate and that water level was central in Cuckoo chick survival. Our study shows that a maintenance of intermediate water levels is the most optimal for maintaining Cuckoo populations in intensive agricultural landscapes. Because brood parasites are excellent bioindicators as their presence predicts regional hotspots of taxonomic and functional diversity as well as population trends in bird communities, knowledge on their habitat requirements is relevant in management targeting diverse bird communities. [ABSTRACT FROM AUTHOR]

Estimating fuel load and potential flight ranges of migrant passerines are basic issues in understanding bird migration strategies. Thirteen sub-Saharan and three pre-Saharan migrant passerine species were analysed in this study. The birds were captured at the Tömörd Bird Ringing Station in the western part of the Carpathian Basin. A general linear model with body mass as the dependent variable and fat score, muscle score and wing length as independent variables were used to estimate lean body mass (body mass without fuel deposits) and fuel load. In ten of the species studied, models considering interactions between factors fit the data better than the main-effect models. Body mass was positively correlated with the fat score in all species, with muscle score in ten species and wing length in 14 species. During autumn, fuel load tended to be larger in the sub-Saharan migrants, especially in four species which pass over the Mediterranean Sea, Common Nightingale (Luscinia megarhynchos), Icterine Warbler (Hippolais icterina), Garden Warbler (Sylvia borin) and Barred Warbler (Curruca nisoria). Nine sub-Saharan migrants, Marsh Warbler (Acro- cephalus palustris), Sedge Warbler (A. schoenobaenus), Eurasian Reed Warbler (A. scirpaceus), European Pied Flycatcher (Ficedula hypoleuca), Spotted Flycatcher (Muscicapa striata), Wood Warbler (Phylloscopus sibilatrix), Willow Warbler (Ph. trochilus), Common Whitethroat (C. communis) and Lesser Whitethroat (C. curruca) had estimated flight ranges similar (<1300 km) to two pre-Saharans, European Robin (Erithacus rubecula) and Eurasian Blackap (S. atricapilla). The three short-distance migrants, including the Common Chiffchaff (Ph. col- lybita) with the shortest distance, had sufficient fuel load to reach their southern European wintering sites without needing to refuel at stopover sites. [ABSTRACT FROM AUTHOR]

Birds were surveyed in Sarobetsu Moor, northern Hokkaido in late June and early July 1961. A total of 26 bird species was recorded in the moor. In central part of the moor dominated by sphagnum only Alauda arvensis was main specis. In western and eastern parts of the moor low shrubs are dominant plants and main bird species were grassland birds such as Gallinago hardwickii, Acrocephalus bistrigiceps, Luscinia calliope, Saxicola torquatus, Emberiza aureola. In forests with small shallow lakes and grassland of Wakasakanai 40 species were recorded. In forest and agricultural lands of Maruyama 19 species were recorded. [ABSTRACT FROM AUTHOR]

In birds, male song is mainly driven by sexual selection, whereby several song characteristics have been demonstrated to be important. In this context, the number of syllables produced per time unit (syllable rate), which thus reflects the "speed" of a song, has been suggested as a reliable indicator of male quality. It has been also shown that syllable rate reflects the aggressive state of an individual. We examined the importance of syllable rate for male–male interactions in unmated, territorial Eurasian Reed Warbler (Acrocephalus scirpaceus) males, for which song plays an important role in territory defense and mate choice, but there is a lack of information about which characteristics might be specifically important for territorial defense. We investigated the behavioral response of the receiver to varying syllable rates. Playback experiments were performed with two playback stimuli representing high and low syllable rates, which were presented simultaneously within the territory of an unmated male. The response of the territory owner was determined using several behavioral parameters and revealed to differ significantly between the two playback treatments with varying song speeds. More males approached first and came closer to the sound of the slow song as well as staying nearby longer. This reaction might indicate that the receiver is intimidated by the more aggressive nature of the fast song type. [ABSTRACT FROM AUTHOR]

The Iberian and North African populations of reed warblers have been described recently as a separate taxon, ambiguus, forming a sister clade to the Sahelian subspecies minor of African Reed Warbler Acrocephalus baeticatus. Although the breeding range of ambiguus has been identified, the migration strategy of its populations remained unknown. We deployed geolocators and sampled the innermost primary from breeding adults in Spain for stable hydrogen (δ2H) analyses and also analysed stable carbon (δ13C) and nitrogen (δ15N) isotopes in feathers collected in two reed warbler taxa (Acrocephalus scirpaceus and Acrocephalus baeticatus ambiguus) in Morocco, to identify the moulting and wintering sites of these populations. Ring recoveries, geolocator tracks and probabilistic assignments to origin from δ2H values indicate that Spanish ambiguus are likely to moult south of the Sahara and winter in West Africa, probably from Mauretania to southern Mali and Ivory Coast. Moroccan ambiguus, however, undergo post‐breeding moult north of the Sahara, and possibly then migrate to West Africa. With other populations of ambiguus breeding from Algeria to Libya and probably wintering further east in the Sahelian belt, the Barbary Reed Warbler can therefore be considered a trans‐Saharan migrant, with a post‐breeding moult strategy that varies between populations, and probably structured according to breeding latitude. [ABSTRACT FROM AUTHOR]

Background: Considerable research has focussed on the importance of bacterial communities within the vertebrate gut microbiome (GM). However, studies investigating the significance of other microbial kingdoms, such as fungi, are notably lacking, despite their potential to influence host processes. Here, we characterise the fungal GM of individuals living in a natural population of Seychelles warblers (Acrocephalus sechellensis). We evaluate the extent to which fungal GM structure is shaped by environment and host factors, including genome-wide heterozygosity and variation at key immune genes (major histocompatibility complex (MHC) and Toll-like receptor (TLR)). Importantly, we also explore the relationship between fungal GM differences and subsequent host survival. To our knowledge, this is the first time that the genetic drivers and fitness consequences of fungal GM variation have been characterised for a wild vertebrate population. Results: Environmental factors, including season and territory quality, explain the largest proportion of variance in the fungal GM. In contrast, neither host age, sex, genome-wide heterozygosity, nor TLR3 genotype was associated with fungal GM differences in Seychelles warblers. However, the presence of four MHC-I alleles and one MHC-II allele was associated with changes in fungal GM alpha diversity. Changes in fungal richness ranged from between 1 and 10 sequencing variants lost or gained; in some cases, this accounted for 20% of the fungal variants carried by an individual. In addition to this, overall MHC-I allelic diversity was associated with small, but potentially important, changes in fungal GM composition. This is evidenced by the fact that fungal GM composition differed between individuals that survived or died within 7 months of being sampled. Conclusions: Our results suggest that environmental factors play a primary role in shaping the fungal GM, but that components of the host immune system—specifically the MHC—may also contribute to the variation in fungal communities across individuals within wild populations. Furthermore, variation in the fungal GM can be associated with differential survival in the wild. Further work is needed to establish the causality of such relationships and, thus, the extent to which components of the GM may impact host evolution. 9CdzjevkYdspZSC-kwkuzt Video Abstract [ABSTRACT FROM AUTHOR]

Nest defense is an effective strategy of hosts against parasites. Typically, hosts will aggressively attack brood parasites that approach or visit their nests, which can prevent the parasites from laying eggs or may even lead to the death of the parasites. Few previous studies have specifically reported such fatal cases involving brood parasites and have attributed the cause of death to either drowning or hypothermia after falling into the water following an attack from hosts. In this study, we recorded the process of multiple host individuals of the Oriental reed warbler (Acrocephalus orientalis) mobbing and attacking a female common cuckoo (Cuculus canorus) in the field. We discovered that the immediate cause of the cuckoo's death was the fatal physical damage resulting from the aggressive defense from the hosts, suggesting that frantic pecking and scratching by the hosts is the most proximate cause of mortality among egg‐laying female cuckoos. This finding enhances our essential understanding of the effectiveness of host attacks. [ABSTRACT FROM AUTHOR]

Telomeres have been advocated to be important markers of biological age in evolutionary and ecological studies. Telomeres usually shorten with age and shortening is frequently associated with environmental stressors and increased subsequent mortality. Telomere lengthening – an apparent increase in telomere length between repeated samples from the same individual – also occurs. However, the exact circumstances, and consequences, of telomere lengthening are poorly understood. Using longitudinal data from the Seychelles warbler (Acrocephalus sechellensis), we tested whether telomere lengthening – which occurs in adults of this species – is associated with specific stressors (reproductive effort, food availability, malarial infection and cooperative breeding) and predicts subsequent survival. In females, telomere shortening was observed under greater stress (i.e., low food availability, malaria infection), while telomere lengthening was observed in females experiencing lower stress (i.e., high food availability, assisted by helpers, without malaria). The telomere dynamics of males were not associated with the key stressors tested. These results indicate that, at least for females, telomere lengthening occurs in circumstances more conducive to self‐maintenance. Importantly, both females and males with lengthened telomeres had improved subsequent survival relative to individuals that displayed unchanged, or shortened, telomeres – indicating that telomere lengthening is associated with individual fitness. These results demonstrate that telomere dynamics are bidirectionally responsive to the level of stress that an individual faces, but may poorly reflect the accumulation of stress over an individuals lifetime. [ABSTRACT FROM AUTHOR]

Simple Summary: Through the examination of several blood metabolites in two migratory warblers at two stopover sites in Portugal, Sedge warblers showed higher values of triglycerides (TRIG) + glycerol (GLY) than Eurasian Reed warblers, both during post-flight fasting and when stopping naturally. The higher values of TRIG + GLY in circulation should reflect a higher fat reserve mobilization by Sedge warblers, attributed to the fewer possibilities to refuel, relying more on fat reserves during their migratory journeys than those of Eurasian Reed warblers. Sedge warblers use more lipids or more efficiently the reserves in each migratory step, due to longer fasting periods causing lower glycaemia levels. Our study revealed differences in the level of unsaturation subcutaneous fatty acids, mainly the higher levels of polyunsaturated fatty acids in Sedge warbler. Differences in preying habits may trigger a series of adaptations that results in different migratory strategies between Sedge and Eurasian Reed warblers. The overall speed of bird migration is limited by the amount of fuel stores acquired during the initial phases of migration. The ability to mobilize fat is crucial for migratory birds that can exhibit different migratory strategies. Birds mobilize triglycerides during nocturnal flight thus increasing circulating fatty acids and glycerol to meet the metabolic demands of flight. Eurasian Reed (Acrocephalus scirpaceus) and Sedge (Acrocephalus schoenobaenus) Warblers were captured at Portuguese stopover sites during spring and autumn migration. These species were selected based on their different migration strategies and dietary preferences during migration. Blood metabolites and fat composition were analyzed to determine their nutritional states. Sedge Warblers had higher blood triglyceride and glycerol levels during post-flight fasting than in non-fasting periods. Furthermore, Sedge Warblers had higher triglyceride and glycerol levels than Eurasian Reed Warblers in both post-flight fasting and non-fasting condition. The differences found may reflect distinct approaches in re-feeding activity (e.g., feeding intensely) associated with the number of stopovers during migratory cycle. Dietary preferences affect the fat composition available for oxidation during long-term exercise in migratory flight. Nuclear magnetic resonance analysis of subcutaneous fat composition revealed that Sedge Warblers presented higher levels of polyunsaturated fatty acid levels than Eurasian Reed Warblers. The distinct lipidic profiles observed and differences in feeding ecology may explain the different migration strategies of these species. Overall and despite their ecological similarity, our study species showed pronounced differences in blood metabolites levels and subcutaneous fatty acids composition, likely attributed to the migratory strategy and foraging preferences during their migratory cycle. [ABSTRACT FROM AUTHOR]

Our aim was to investigate the among-populations diversity of prey composition in Eurasian Reed Warblers' diets via their droppings, both to assess the ecological validity of this sampling method and to test whether the prey species most abundant in fecal samples were also the most present in the Italian study site. We collected fecal samples at four sites throughout Italy, for a total of 144 samples. Within reedbeds, the breeding habitat of the Eurasian Reed Warbler, we also collected arthropods by carrying out entomological sweepings at one of the study sites. Within the fecal samples, we identified dozens of prey species, belonging mainly to Araneae, Coleoptera, Diptera, Hymenoptera and Aphidoidea taxa, whose compositions were not statistically different among sites. The commonest prey species were Coleoptera in the droppings (68.5%) and Diptera in the reedbeds (31.3%), although the latter was less numerous in the fecal samples. The diets of different Italian populations of Eurasian Reed Warbler emerging from our study underline a strong Coleopteran presence, without differences across Italy. Fecal samples appear to be an exhaustive method to study variation in Eurasian Reed Warbler diet and its ecological importance; however, although potential caveats do exist, such as the possible under-representation of Diptera. [ABSTRACT FROM AUTHOR]

Distress calls, as a type of alarm call, play important roles in expressing bodily condition and conveying information concerning predation threats. In this study, we examined the communication via distress calls in parent–offspring and inter-offspring interactions. First, we used playback of chick distress calls of 2 sympatric breeders, the vinous-throated parrotbill Sinosuthora webbiana and the oriental reed warbler Acrocephalus orientalis , to the adults/chicks of these 2 species, respectively, and measured the responses of conspecifics or heterospecifics. The playback-to-chicks experiment showed that both species of chicks reduced the number of begging calls and begging duration time as a response to conspecific/heterospecific distress calls compared with natural begging and background noise controls. However, reed warbler chicks also reduced beak opening frequency in the response to conspecific distress calls compared with other playback stimuli. Second, the results of the playback-to-adults experiment showed that reed warbler adults could eavesdrop on distress calls of conspecific neighbors and sympatric heterospecifics. Furthermore, the nest-leaving behavior of reed warblers did not differ significantly when they heard the distress calls of conspecifics or parrotbills. Finally, reed warbler adults responded to heterospecific distress calls more quickly than to conspecific distress calls, and parrotbill adults presented the same response. Our results supported the warn-kin hypothesis and show that chick distress calls play an important role in conveying risk and the condition of chicks to enhance individual fitness. In addition, we also found that eavesdropping on distress calls is a congenital behavior that begins in the chick stage. [ABSTRACT FROM AUTHOR]

In some populations of the host of brood parasites, more than two parasite eggs may be laid in a single nest. This phenomenon is known as multiple parasitism, representing a cost to both the host and parasite. In this study, we analysed a long-term dataset (2007–2021) focusing on multiple parasitism of the common cuckoo (Cuculus canorus) parasitizing the great reed warbler (Acrocephalus arundinaceus). The annual parasitism rate was on average 54.3% and varied between 5.8% and 92.2%, depending on the year. Out of 720 parasitized nests, double parasitism was recorded in 172 (23.9%) nests, triple in 51 (7.1%) nests, quadruple in 10 (1.3%) nests, and, exceptionally, in the years of heavy parasitism (about 90%), quintuple parasitism was recorded in three (0.4%) nests. The rate of multiple parasitism ranged from 0 to 63% inter-annually and strongly correlated with the parasitism rate and the total number of parasite eggs found. Furthermore, the number of cuckoo eggs laid per one nest increased with the decreasing daily availability of host nests that were at a suitable breeding stage for parasitism. Both genetic and egg phenotype analyses revealed that no cuckoo female laid more than one egg in the same host nest. Using data on long-term parasite–host interactions and from continuous video recording, as well as progressive methods to assign parasite offspring thus helped us better understand various aspects of multiple parasitism in hosts heavily parasitized by an evictor brood parasite. Significance statement: Laying more parasite eggs in one host nest (i.e. multiple parasitism) is common in brood parasites whose nestlings share the nest with nestmates. In the species where the parasite's nestling kills its nest mates, multiple parasitism should be rare because it is costly for the parasite. However, in host populations with high parasitism rates, multiple parasitism occurs more often than predicted. Using long-term and video-recording data, we quantified multiple parasitism in the common cuckoo across years and host egg-laying sequences. We found that the rate of multiple parasitism is positively related to the parasitism rate and that the lower the number of nests suitable for parasitism, the higher the number of parasite eggs in one nest. Based on genetic and egg phenotype analyses, we also showed that individual parasitic females avoid laying in the nests they had already parasitized. [ABSTRACT FROM AUTHOR]

Classical models predict that male fitness is based on resources monopolized and invested in reproduction, and/or on individual quality providing offspring with sexually attractive traits or viable genes. However, these factors are frequently correlated, making their relative influence on male fitness difficult to describe and quantify. We analysed the relative influence of the main features of the sedge warbler's Acrocephalus schoenobaenus breeding system, i.e. age, arrival date, territory quality, male sexual activity (song and polyterritorial behaviour), on males' mating success, fledging success and local recruitment. Results show that this species' breeding system involves three main paths: 1) earlier‐arriving males have higher mating success, regardless of territory quality, 2) the quality of territories pre‐empted by earlier males directly influences recruitment and 3) mating success is influenced by male sexual activity (polyterritorial behaviour), but an additional territory also affects recruitment directly. As arrival date plays a significant role in all the paths, the whole system seems to depend on male quality; although the benefits accruing to male fitness are obtained not only through sexual selection but also through resource monopolization. [ABSTRACT FROM AUTHOR]

The reproductive period in animals is a demanding part in their life history. In birds, environmental factors, such as adverse weather, predation, or brood parasitism; and/or anthropogenic disturbance, can limit breeding success, resulting in failure of clutches. The nest loss in open‐cup nesting passerines is usually replaced with a new nest with a new clutch, however, in some cases the clutch replacement may occur in unusual forms. In this study, we report on three cases of within‐season nest reuse in the Great Reed Warbler. In the first case, a nest was reused for two times in the same season after unsuccessful nesting attempts (two‐time nest reuse). After the nest was depredated the first time, the female laid new eggs that were depredated again, then again the female laid new eggs that produced four fledglings. In the second case, the first clutch was depredated, after which the female laid a new clutch in the same nest that was again depredated. In the third case, the female laid new eggs among the eggs that failed to hatch previously. Our observations tend not to be consistent with the predator avoidance hypothesis because the depredated nests were reused by the parents. The time/energy saving hypothesis or possible deterrence of nest parasitism could explain nest reuse in this study, but because of low number of nests reused compared to the total number of nests found, this phenomenon needs further clarification. [ABSTRACT FROM AUTHOR]

Hosts of avian brood parasites suffer a high cost of reproductive loss due to parasitism, driving them to evolve a variety of anti-parasitic defenses. These defenses comprise a series of components, including the recognition of brood parasites and the eggs laid by the parasites, cues used for recognition, and the mechanisms on which these behaviors are based. In this study, we conducted egg recognition and nest intruder experiments to examine these components of anti-parasitic behavior in the black-browed reed warbler (Acrocephalus bistrigiceps), a rare host of the common cuckoo (Cuculus canorus). We found that the host possessed strong recognition capacity, rejecting 100% of parasitic eggs, and used a template-based mechanism for egg recognition. The host birds also rejected 80% of their own eggs on which artificial markings were added to the blunt pole; however, they accepted all eggs with the same manipulation on the sharp pole, implying that the blunt pole was an important recognition cue. Furthermore, the host exhibited stronger aggression to cuckoos than to harmless controls; a behavior specific to the incubation stage rather than the nestling stage. Therefore, the host was able to distinguish the cuckoo from other nest intruders as being a brood parasite. These results together help explain the near absence of cuckoo parasitism in black-browed reed warblers and provide new information concerning anti-parasitic defenses in this host species. [ABSTRACT FROM AUTHOR]

The major histocompatibility complex (MHC) plays a central role in the vertebrate adaptive immune system and has been of long‐term interest in evolutionary biology. While several protocols have been developed for MHC genotyping, there is a lack of transparent and standardized tools for downstream analysis of MHC data. Here, we present the r package mhctools and demonstrate the use of its functions to (i) assist accurate MHC genotyping from high‐throughput amplicon‐sequencing data, (ii) infer functional MHC supertypes using bootstrapped clustering analysis, (iii) identify segregating MHC haplotypes from family data, and (iv) analyse functional and genetic distances between MHC sequences. We employed mhctools to analyse MHC class I (MHC‐I) amplicon data of 559 great reed warblers (Acrocephalus arundinaceus). We identified 390 MHC‐I alleles which clustered into 14 functional supertypes. A phylogenetic analysis and analyses of positive selection suggested that the MHC‐I alleles belong to several distinct functional groups. We furthermore identified 107 segregating haplotypes among 116 families, and found substantial variation in diversity with 4–21 MHC‐I alleles and 3–13 MHC‐I supertypes per haplotype. Finally, we show that the great reed warbler haplotypes harboured combinations of MHC‐I supertypes with greater functional divergence than observed in simulated populations of possible haplotypes, a result that is in accordance with the divergent allele advantage hypothesis. Our study demonstrates the power of mhctools to support genotyping and analysis of MHC in non‐model species, which we hope will encourage broad implementation among researchers in MHC genetics and evolution. [ABSTRACT FROM AUTHOR]

The beginning of reproduction is usually accompanied by a series of decisions including where to establish a territory, attract a mate, to lay eggs or give birth. These decisions might be influenced by the quality of potential partners but also conspecific neighbours. In birds, the quality of an individual can be signaled by song features, like song complexity. Besides choosing the right location for reproduction and mate attraction, we propose here that song may also influence the reproductive investment, in particular early maternal investment, which is known to be a sensitive determinant reflecting different allocation of females in relation to male quality and attractiveness. Here, we examined whether song quality of conspecific neighbours can stimulate various reproductive parameters in European Common Reed Warblers (Acrocephalus scirpaceus). Therefore, we performed field playback experiments advertising song of high and low complexity and examined their influence on settlement decisions, early maternal investment, and breeding success. The number of nests and start of egg laying did not differ between the two playback types but nests were significantly closer to high complex song playbacks. Furthermore, in the high complex song group, a significantly higher proportion of eggs was fully dark pigmented than in the low complex playback group. Nests near high complex playbacks were significantly more successful and significantly more offspring were produced. The results are discussed in relation to whether males use song to stimulate female investment and whether establishing a breeding location near a high-quality neighbour may be an additional aspect in settlement decisions. [ABSTRACT FROM AUTHOR]

Our study reveals for the first time in a quantitative manner the differences in eggshell thickness and elemental composition between pigment spots and adjacent plain eggshell regions in bird species from three developmental modes, i.e. altricial (Great Reed Warbler Acrocephalus arundinaceus), semi-precocial (Black-headed Gull Chroicocephalus ridibundus, Mediterranean Gull Ichthyaetus melanocephalus, Sandwich Tern Thalasseus sandvicensis and Black Tern Chlidonias niger) and precocial species (Western Capercaillie Tetrao urogallus and Black Grouse Lyrurus tetrix). From a broader biological/biogeochemical perspective, our data broaden the knowledge in the heterogeneity of elemental composition between adjacent spotted-plain regions of eggshells, previously demonstrated in galliform birds, which differ in colour for many chemical elements. These differences, however, were distinctive of individual species and varied between chemical elements. There emerged a clear and consistent trend of higher elemental concentrations within pigment spots compared to plain eggshell regions, particularly in the case of five elements: C, Pb, Cu, Cr and Al. The most important and novel finding of our study is that even though the eggshells of gulls and terns (semi-precocial species) and of the passerine (altricial species) were thinner in the spotted regions (there was thus less shell material) compared with those of precocials (the eggshells being thicker eggshells at the spots), the spotted regions of all these eggs contained disproportionally higher concentrations of most major and minor chemical elements. Hence, this appears to be a general rule across all birds, regardless of the eggshell thickness in the spotted or plain regions and/or their developmental mode. In other words, this finding confirms that the thickness of the eggshell itself does not affect the concentrations of elements, and that the key issue related to this is the presence of one or more protoporphyrin layers along with the accompanying pool of chemical elements within the spotted eggshell region. [ABSTRACT FROM AUTHOR]