DNA metabarcoding and stable isotope analysis have significantly advanced our understanding of marine trophic ecology, aiding systematic research on foraging habits and species conservation. In this study, we employed these methods to analyse faecal and blood samples, respectively, to compare the trophic ecology of two Red-billed Tropicbird (Phaethonaethereus; Linnaeus, 1758) colonies on Mexican islands in the Pacific. Trophic patterns among different breeding stages were also examined at both colonies. Dietary analysis reveals a preference for epipelagic fish, cephalopods, and small crustaceans, with variations between colonies and breeding stages. Isotopic values (δ15N and δ13C) align with DNA metabarcoding results, with wider niches during incubation stages. Differences in diet are linked to environmental conditions and trophic plasticity among breeding stages, influenced by changing physiological requirements and prey availability. Variations in dietary profiles reflect contrasting environmental conditions affecting local prey availability.

Monitoring trends in wildlife communities is integral to making informed land management decisions and applying conservation strategies. Birds inhabit most niches in every environment and because of this they are widely accepted as an indicator species for environmental health. Traditionally, point counts are the common method to survey bird populations, however, passive acoustic monitoring approaches using autonomous recording units have been shown to be cost-effective alternatives to point count surveys. Advancements in automatic acoustic classification technologies, such as BirdNET, can aid in these efforts by quickly processing large volumes of acoustic recordings to identify bird species. While the utility of BirdNET has been demonstrated in several applications, there is little understanding of its effectiveness in surveying declining grassland birds. We conducted a study to evaluate the performance of BirdNET to survey grassland bird communities in Nebraska by comparing this automated approach to point count surveys. We deployed ten autonomous recording units from March through September 2022: five recorders in row-crop fields and five recorders in perennial grassland fields. During this study period, we visited each site three times to conduct point count surveys. We compared focal grassland bird species richness between point count surveys and the autonomous recording units at two different temporal scales and at six different confidence thresholds. Total species richness (focal and non-focal) for both methods was also compared at five different confidence thresholds using species accumulation curves. The results from this study demonstrate the usefulness of BirdNET at estimating long-term grassland bird species richness at default confidence scores, however, obtaining accurate abundance estimates for uncommon bird species may require validation with traditional methods.

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Human cases of avian influenza virus (AIV) infections are associated with an age-specific disease burden. As the influenza virus N2 neuraminidase (NA) gene was introduced from avian sources during the 1957 pandemic, we investigate the reactivity of N2 antibodies against A(H9N2) AIVs. Serosurvey of healthy individuals reveal the highest rates of AIV N2 antibodies in individuals aged ≥65 years. Exposure to the 1968 pandemic N2, but not recent N2, protected against A(H9N2) AIV challenge in female mice. In some older adults, infection with contemporary A(H3N2) virus could recall cross-reactive AIV NA antibodies, showing discernable human- or avian-NA type reactivity. Individuals born before 1957 have higher anti-AIV N2 titers compared to those born between 1957 and 1968. The anti-AIV N2 antibodies titers correlate with antibody titers to the 1957 N2, suggesting that exposure to the A(H2N2) virus contribute to this reactivity. These findings underscore the critical role of neuraminidase immunity in zoonotic and pandemic influenza risk assessment.

Feather moulting is a crucial process in the avian life cycle, which evolved to maintain plumage functionality. However, moulting involves both energetic and functional costs. During moulting, plumage function temporarily decreases between the shedding of old feathers and the full growth of new ones. In flying taxa, a gradual and sequential replacement of flight feathers evolved to maintain aerodynamic capabilities during the moulting period. Little is known about the moult strategies of non-avian pennaraptoran dinosaurs and stem birds, before the emergence of crown lineage. Here, we report on two Early Cretaceous pygostylian birds from the Yixian Formation (125 mya), probably referable to Confuciusornithiformes, exhibiting morphological characteristics that suggest a gradual and sequential moult of wing flight feathers. Short primary feathers interpreted as immature are symmetrically present on both wings, as is typical among extant flying birds. Our survey of the enormous collection of the Tianyu Museum confirms previous findings that evidence of active moult in non-neornithine pennaraptorans is rare and likely indicates a moult cycle greater than one year. Documenting moult in Mesozoic feathered dinosaurs is critical for understanding their ecology, locomotor ability and the evolution of this important life-history process in birds.

The major histocompatibility complex (MHC) multigene family encodes key pathogen-recognition molecules of the vertebrate adaptive immune system. Hyper-polymorphism of MHC genes is de novo generated by point mutations, but new haplotypes may also arise by re-shuffling of existing variation through intra- and inter-locus gene conversion. Although the occurrence of gene conversion at the MHC has been known for decades, we still have limited understanding of its functional importance. Here, I took advantage of extensive genetic resources (~9000 sequences) to investigate broad scale macroevolutionary patterns in gene conversion processes at the MHC across nearly 200 avian species. Gene conversion was found to constitute a universal mechanism in birds, as 83% of species showed footprints of gene conversion at either MHC class and 25% of all allelic variants were attributed to gene conversion. Gene conversion processes were stronger at MHC-II than MHC-I, but inter-specific variation at both MHC classes was explained by similar evolutionary scenarios, reflecting fluctuating selection towards different optima and drift. Gene conversion showed uneven phylogenetic distribution across birds and was driven by gene copy number variation, supporting significant role of inter-locus gene conversion processes in the evolution of the avian MHC. Finally, MHC gene conversion was stronger in species with fast life histories (high fecundity) and in long-distance migrants, likely reflecting variation in population sizes and host-pathogen coevolutionary dynamics. The results provide a robust comparative framework for understanding macroevolutionary variation in gene conversion at the avian MHC and reinforce important contribution of this mechanism to functional MHC diversity.

UNASSIGNED: Invasive species are the primary threat to island ecosystems globally and are responsible for approximately two-thirds of all island species extinctions in the past 400 years. Non-native mammals-primarily rats, cats, mongooses, goats, sheep, and pigs-have had devastating impacts on at-risk species and are major factors in population declines and extinctions in Hawai\'i. With the development of fencing technology that can exclude all mammalian predators, the focus for some locations in Hawai\'i shifted from predator control to local eradication.
UNASSIGNED: This article describes all existing and planned full predator exclusion fences in Hawai\'i by documenting the size and design of each fence, the outcomes the predator eradications, maintenance issues at each fence, and the resulting native species responses.
UNASSIGNED: Twelve predator exclusion fences were constructed in the Hawaiian Islands from 2011-2023 and six more were planned or under construction; all were for the protection of native seabirds and waterbirds. Fences ranged in length from 304-4,877 m and enclosed 1.2-640 ha. One-third of the 18 fences were peninsula-style with open ends; the remaining two-thirds of the fences were complete enclosures. The purpose of twelve of the fences (67%) was to protect existing bird populations, and six (33%) were initiated for mitigation required under the U.S. Endangered Species Act. Of the six mitigation fences, 83% were for the social attraction of seabirds and one fence was for translocation of seabirds; none of the mitigation fences protected existing bird populations. Rats and mice were present in every predator exclusion fence site; mice were eradicated from five of six sites (83%) where they were targeted and rats (three species) were eradicated from eight of 11 sites (72%). Mongoose, cats, pigs, and deer were eradicated from every site where they were targeted. Predator incursions occurred in every fence. Rat and mouse incursions were in many cases chronic or complete reinvasions, but cat and mongoose incursions were occasional and depended on fence type (i.e., enclosed vs. peninsula). The advent of predator exclusion fencing has resulted in great gains for protecting existing seabirds and waterbirds, which demonstrated dramatic increases in reproductive success and colony growth. With threats from invasive species expected to increase in the future, predator exclusion fencing will become an increasingly important tool in protecting island species.

BACKGROUND: Migratory birds exhibit heterogeneity in foraging strategies during wintering to cope with environmental and migratory pressures, and gut bacteria respond to changes in host diet. However, less is known about the dynamics of diet and gut fungi during the wintering period in black-necked cranes (Grus nigricollis).
RESULTS: In this work, we performed amplicon sequencing of the trnL-P6 loop and ITS1 regions to characterize the dietary composition and gut fungal composition of black-necked cranes during wintering. Results indicated that during the wintering period, the plant-based diet of black-necked cranes mainly consisted of families Poaceae, Solanaceae, and Polygonaceae. Among them, the abundance of Solanaceae, Polygonaceae, Fabaceae, and Caryophyllaceae was significantly higher in the late wintering period, which also led to a more even consumption of various food types by black-necked cranes during this period. The diversity of gut fungal communities and the abundance of core fungi were more conserved during the wintering period, primarily dominated by Ascomycota and Basidiomycota. LEfSe analysis (P < 0.05, LDA > 2) found that Pyxidiophora, Pseudopeziza, Sporormiella, Geotrichum, and Papiliotrema were significantly enriched in early winter, Ramularia and Dendryphion were significantly enriched in mid-winter, Barnettozyma was significantly abundant in late winter, and Pleuroascus was significantly abundant in late winter. Finally, mantel test revealed a significant correlation between winter diet and gut fungal.
CONCLUSIONS: This study revealed the dynamic changes in the food composition and gut fungal community of black-necked cranes during wintering in Dashanbao. In the late wintering period, their response to environmental and migratory pressures was to broaden their diet, increase the intake of non-preferred foods, and promote a more balanced consumption ratio of various foods. Balanced food composition played an important role in stabilizing the structure of the gut fungal community. While gut fungal effectively enhanced the host\'s food utilization rate, they may also faced potential risks of introducing pathogenic fungi. Additionally, we recongnized the limitations of fecal testing in studying the composition of animal gut fungal, as it cannot effectively distinguished between fungal taxa from food or soil inadvertently ingested and intestines. Future research on functions such as cultivation and metagenomics may further elucidate the role of fungi in the gut ecosystem.

BACKGROUND: Parent-offspring conflict represents the sensitive balance of resource allocation between self-maintenance and reproduction. Two strategies have been proposed to better understand how species manage this conflict. In fixed-level feeding behavior, parents feed offspring consistent quantities of food; while flexible feeding shows plasticity in parental allocation based on offspring need. Life-history theory predicts that parents of long-lived species prioritize their survival and may favor the fixed-level hypothesis to maximize lifetime reproductive success. In this study, we highlight the natural variation of parent-offspring allocation strategies within a unique population of Leach\'s storm-petrels (Hydrobates leucorhous), and through month-long food supplementation and restriction manipulations, we investigate how chick condition affects parental provisioning during the chick-rearing period of reproduction.
RESULTS: We show that the parents upregulated chick feeding frequency of nutritionally deprived chicks, resulting in a larger total amount of food delivered during the study period. Additionally, the proportion of nights when both parents fed was highest in restricted chicks, and the proportion of nights when neither parents fed was lowest in restricted chicks, suggesting that storm-petrel parents shorten their foraging bouts to deliver food more often when their chicks are in relatively poor condition.
CONCLUSIONS: Our results support that Leach\'s storm-petrels use a flexible-level feeding strategy, suggesting that parents can assess offspring condition, and respond by feeding chicks at higher frequencies. These data provide insight on how a long-lived seabird balances its own energetic demands with that of their offspring during the reproductive period.

The appropriate structure of the digestive tract is crucial for individual adaptation to ecological conditions. In birds, the length of the small intestine, responsible for food absorption, is generally believed to be positively correlated with body size. In this study, we investigated the variation in small intestine length in the White Stork (Ciconia ciconia), a monomorphic species without visible sexual dimorphism, but characterized by differing parental efforts, which can be reflected by the small intestine lengths between the sexes. We examined the relationship between small intestine length and body size within the sexes. Our findings show that male White Storks have significantly shorter small intestines than females, despite having larger body sizes than the latter. Furthermore, we found a significant relationship between body size and small intestine length, but it was of a different nature in the two sexes. Males exhibited a previously unreported phenomenon, whereby increasing body size was associated with shortening small intestines, whereas females exhibited the opposite pattern. These novel findings shed light on the anatomical adaptations of the digestive tract in birds.