The rate of new mutations is the ultimate source of genetic variation, and thus, a fundamental quantity in evolution. Mutation rates vary across the tree of life, influenced by selection pressures and life-history traits. Within species, mutation rates and types show subtle differences between sexes as well as a positive association with parental age. Most of the direct estimates come from a few mammal species, often primates, and their generality has not been fully realised. Using 33 parent-offspring trios, we investigate the mutation rate in the barn owl ( Tyto alba ) and show that this species has a mutation rate of 5.6 × 10 −9 , matching rates of passerine species with a similar generation time of 2-3 years. Using different phasing methods we show that fathers pass on twice as many mutations as mothers and identify subtle differences in the sex-specific spectra of mutations. We also find that the number of mutations increases with paternal age, bringing direct evidence for germline senescence in birds. While across-species mutation rates and types appear conserved, the potential for within species variation due to age is substantial.

Despite its detrimental effects, inbreeding depression in wild populations is relatively under-explored. Here, we use whole-genome sequence data from more than 2700 wild barn owls (Tyto alba) to investigate the presence, severity and genetic architecture of inbreeding depression in three morphological traits. Using linear models (accounting for age) and nonlinear models (measuring growth effects) we show evidence for inbreeding depression. Moreover, by partitioning developmental stages we improve our ability to detect it, as in some traits we find that it manifests during juvenile growth, and in others during adulthood. These trait-specific patterns may reflect changes in environmental influences, as we also find that juvenile heritability is lower. We additionally use two genomic inbreeding coefficients: FROH and FUniW, and while both showed the same direction of effect, the strength of evidence for inbreeding depression differs. This discrepancy offers some insight into the frequency distribution of responsible variants, as the coefficients weight variants differently based on their frequencies. Finally, an assessment of local genomic inbreeding effects highlights a handful of genomic regions with significantly deleterious effects when homozygous, alongside many regions with a smaller contribution. Overall, we provide a detailed examination of inbreeding depression affecting morphological and growth traits in this wild population.

Bright coloration in predators presents a paradox: being highly visible should reduce hunting success, yet vivid colors persist in species that rely on stealth. Camouflage, which minimizes contrast with the background, and startle coloration, where sudden brightness disrupts prey escape, have been proposed to explain this paradox. Barn owls (Tyto alba) are polymorphic, ranging from dark reddish to bright white, offering a natural experiment. Using high-resolution biologging, we tracked 69 free-ranging males across 354 nights and recorded 17,600 hunting attempts during chick provisioning. We tested whether plumage color mediates moonlight-dependent hunting behavior and performance. White males reduced exposure under dim conditions but, under bright moonlight, oriented attacks toward the Moon and favored bright periods and unshaded sites throughout the night. Red males showed weaker or no adjustments and remained comparatively cryptic. Although per-attack success did not differ across the lunar gradient, white males achieved higher nightly prey capture rates and shorter foraging bouts under bright moonlight. Together with previous work, these patterns are more consistent with the startle hypothesis than with a pure background-matching scenario, suggesting that conspicuous plumage can be incorporated into a light-dependent hunting strategy and that variation in lunar lightscapes may influence the evolution of animal coloration.

The rate of new mutations is the ultimate source of genetic variation, and thus, a fundamental quantity in evolution. Mutation rates vary across the tree of life, influenced by selection pressures and life-history traits. Within species, mutation rates and types show differences between sexes as well as a positive association with parental age. Most of the direct estimates come from a few mammal species, often primates, and their generality has not been fully realized. Using 33 parent-offspring trios, we investigate the mutation rate in the barn owl (Tyto alba) and show that the species has a mutation rate of 4.96 × 10-9 per site per generation, matching rates of passerine species with a similar generation time of 2 to 3 years. Using read- and trio-based phasing methods we find that fathers pass on twice as many mutations as mothers and identify subtle differences in the sex-specific spectra of mutations. We also show that the number of mutations increases with paternal age, bringing direct evidence for germline senescence in birds. While across-species mutation rates and types appear conserved, the potential for within species variation due to age is substantial.

Whole genome sequencing (WGS) of a large number of samples is costly. Solutions include targeting a proportion of the genome (eg SNP arrays) or lowering the sequencing depth (low-coverage WGS, lcWGS) but both approaches suffer from either genotype missingness or uncertainty. Genomic imputation addresses this problem by inferring missing or uncertain genotypes using a collection of high quality genomic data (reference panel). However, certain methods can impute a lcWGS dataset without a reference panel. Because generating a reference panel can be prohibitively expensive in nonmodel species, a benchmarking of the accuracy of these alternative methods of imputation can help inform study design. Here, we imputed a dataset of 2,800 barn owls (Tyto alba) sequenced in lcWGS in the presence and absence of a reference panel of 502 samples. We used 32 individuals sequenced at both high and low coverage to estimate the accuracy of each method and explored the limitations of lcWGS sample size and reference panel size. Although the best results were achieved with a large reference panel, using only a lcWGS dataset showed very accurate imputation, when over 500 samples were used and we account for missing data and low frequency alleles. In addition, imputation with or without a reference panel returned similar results in a GWAS of a polygenic trait but caution was required when comparing identified homozygous-by-descent segments. Thus, while using a reference panel remains the ideal approach, imputation in suitably large lcWGS datasets can provide sufficient accuracy given proper quality control.

Psychologists have long known that contact with and exposure to so-called outgroup members can help overcome separation, including those resulting from entrenched conflicts. Getting to know each other facilitates understanding and fosters tolerance, whether we think of national, religious, cultural, socio-economic or age divides. Thus, we here expand the concept of Environmental Peacebuilding to Environmental Bridgebuilding, because sharing knowledge and practices around nature conservation objectives offers opportunities to find common ground for individuals and groups. With Environmental Bridgebuilding, we are emphasising the connectivity effects of nature conservation planning and implementation. Due to our shared experiences, we take our work with the barn owl, Tyto alba, as an example to discuss Environmental Bridgebuilding. This choice does not limit Environmental Bridgebuilding to this species, on the contrary. Moreover, we discuss psychological factors in addition to between-subgroup and intergroup challenges that might impact the success of socially engaging nature conservation initiatives, as well as the need for the combined expertise from various professions, such as biologists, psychologists, farmers and economists. Ecology and science more generally can be an inspiring source to bring together people that life has divided.

Abstract Although local adaptation influences species distributions, its role in driving evolutionary resilience under climate change remains unclear. Current predictive models focus on genetic adaptation to present climates, providing limited insight into future adaptive capacity. We hypothesise that historical responses to climatic shifts can reveal candidate loci for local adaptation in the future. Combining ecological niche modelling and genomic analyses, we investigate spatiotemporal patterns and mechanisms of local adaptation of the Western Palearctic barn owl ( Tyto alba ). Ecological modelling reveals that barn owls now occupy a broader climatic niche than during the Last Glacial Maximum. Genomic analyses indicate ongoing adaptation, with regions under selection linked to environmental factors across all populations. We find that local adaptation drives evolutionary changes across populations, enabling colonisation of new habitats and shaping responses to climate change in resident populations. We show that standing genetic diversity plays a crucial role in adaptation to past, present, and future environmental shifts.

From 1971 through 2024, we examined 65,126 Common Barn-Owls (Tyto alba) for rare plumages across the Czech Republic, France, Germany, Great Britain, Israel, and Switzerland. Of these, eight displayed rare plumages. We observed three albino siblings with red irises and white plumage in the Czech Republic. Additionally, we identified one leucistic owl in the Czech Republic, as well as one in Germany and one in Israel, each characterized by black irises and white plumage. We also found two melanistic individuals in the Czech Republic, each with black irises and dark gray plumage. Overall, rare plumages were found in six of 15,157 (0.040%) barn owls in the Czech Republic, and in two of 49,969 (0.004%) in the other five countries studied. Thus, barn owls with rare plumages were more common in the Czech Republic than in the other regions. Given the small number of birds with rare plumages, there seemed to be no population-level implications from these findings. However, there may be implications for the individuals with rare plumages. Notably, one of the leucistic birds (16.7%) was shot, possibly because its white coloration made it more noticeable than a typical-plumaged owl. Future research could compare these findings with observations of rare-plumaged individuals in rehabilitation facilities to determine if rare plumage rates are consistent across different contexts.

Recent advances in long-read sequencing have enabled near telomere-to-telomere (T2T) assemblies across diverse taxa. However, avian genomes remain challenging due to numerous microchromosomes, small, typically < 20Mb, DNA molecules that are gene-, GC-, and repeat-rich. As a consequence, microchromosomes are often missing from genome assemblies. Here, we present a chromosome-level, haplotype-resolved genome assembly for the Western barn owl (Tyto alba). Using a trio-binning strategy with Illumina parental reads combined with PacBio HiFi and Oxford Nanopore Technologies data, we generated two phased contig sets. These were scaffolded into 40 linkage groups using a linkage map. Comparative analyses identified unplaced HiFi scaffolds corresponding to microchromosomes, which we integrated into six additional microchromosomes using long reads information. The two assemblies present 46 chromosomes, matching the karyotype of the species. They exhibit strong synteny between parental haplotypes, except for a ∼38 Mb complex region on chromosome 7 containing nested inversions. This high-quality reference provides a haplotype-resolved and chromosome-level genome for Strigiformes, enabling fine-scale studies of structural variation and avian genome evolution.

Natural selection has rarely promoted the evolution of colour polymorphism in wild mammals. However, it is more common in domestic mammals due to artificial selection. For this reason, domestication could provide valuable insights into the mechanisms underlying the evolution of colour diversity. This raises the question of whether the associations between coat colour and other phenotypes in domestic animals are similar to those in free-living animals. Our literature review of cows, goats and sheep suggests that these associations can differ not only between species but also within and between breeds. This pattern holds for all the traits that we considered: morphology, behaviour, physiology, reproduction, milk production and parasitism. The only consistent association we found in the literature was the attraction of flies towards dark-coloured cows. The relationships between same colour morph, cortisol and thermoregulation varied across environments, suggesting a possible condition-dependent expression of multiple traits. We conclude that artificial selection may lead to a different integration of multiple phenotypes compared to animals living in the wild. Therefore, colour variation may not always serve the same functional roles in domestic animals as it does in wild ones.

ABSTRACTThe installation of automatic detection systems (ADSs) on operating wind energy facilities is a mitigation measure to reduce bird collisions. The effectiveness of an ADS depends on a combination of parameters, including the detection distance of the bird, its flight speed, and the time to complete the chosen action (e.g., turbine shutdown). We created a web application, Eoldist, to calculate cautionary detection distances required by an ADS, using bird flight speed and turbine shutdown time as input parameters. We compiled a database of the flight speeds of 168 Western Palearctic birds from a review of scientific literature supplemented by an analysis of unpublished GPS‐tracking datasets. To estimate turbine shutdown time, we conducted 137 field trials of experimental shutdown at seven wind farms and found that the duration to reach residual rotor speeds of 3 or 2 rotations per minute (rpm) was respectively 32.2 or 38.8 s on average. Based on this data, Eoldist allows the user to select a species from the database, wind turbine characteristics, and a residual rotor speed (3 or 2 rpm); it then calculates the time to reach the selected threshold and provides a distribution curve for the cautionary detection distance needed to prevent collision. This article includes examples of cautionary detection distances required for several species to demonstrate the sensitivity of key input parameters. Eoldist is freely available and should help the wind energy industry, ADS suppliers, and environmental agencies to define requirements for ADS bird detection that are compatible with the biology of the target species.

Homologous recombination is a meiotic process that generates diversity along the genome and interacts with all evolutionary forces. Despite its importance, studies of recombination landscapes are lacking due to methodological limitations and limited data. Frequently used approaches include linkage mapping based on familial data that provides sex-specific broad-scale estimates of realized recombination and inferences based on population linkage disequilibrium that reveal a more fine-scale resolution of the recombination landscape, albeit dependent on the effective population size and the selective forces acting on the population. In this study, we use a combination of these 2 methods to elucidate the recombination landscape for the Afro-European barn owl (Tyto alba). We find subtle differences in crossover placement between sexes that lead to differential effective shuffling of alleles. Linkage disequilibrium-based estimates of recombination are concordant with family-based estimates and identify large variation in recombination rates within and among linkage groups. Larger chromosomes show variation in recombination rates, while smaller chromosomes have a universally high rate that shapes the diversity landscape. We find that recombination rates are correlated with gene content, genetic diversity, and GC content. We find no conclusive differences in the recombination landscapes between populations. Overall, this comprehensive analysis enhances our understanding of recombination dynamics, genomic architecture, and sex-specific variation in the barn owl, contributing valuable insights to the broader field of avian genomics.

In biparental species, reproductive success is influenced by the quality of the parents, the care each provides, environmental factors, and the cooperation between parents in sharing reproductive tasks. Hormones like corticosterone, which modulate physiological and behavioural functions associated with reproductive success, likely play a critical role in reproductive success through hormonal compatibility between breeding partners. Here, we investigate how similarity or dissimilarity in corticosterone levels between barn owl (Tyto alba) breeding partners are related to reproductive success. Using data from 2004 to 2018, we analyzed baseline and stress-induced corticosterone to explore correlations between partners' corticosterone levels and their association with key fitness parameters including clutch size, offspring number, and rearing success. We found that while partners' corticosterone levels do not predict clutch size, they are a significant predictor of offspring number and rearing success. Pairs with dissimilar baseline and stress-induced corticosterone produced more fledglings than pairs with similar corticosterone levels. To evaluate the potential advantage or disadvantage of growing up in large broods, we further examined the effect of brood size on offspring quality and survival. Nestlings from smaller broods had better body condition than those from larger broods, and individuals with better condition were more likely to survive their first year. These findings suggest that barn owl reproductive success is influenced by the combined corticosterone profiles of both parents and indicate a potential trade-off between offspring quantity and quality. This study highlights the importance of considering both parents' hormonal profiles when evaluating corticosterone's role in reproduction among biparental species.

Despite its potentially devastating effects, the prevalence and underlying mechanisms of inbreeding depression in wild populations are still relatively under-explored. Here, we use whole-genome sequence data from >3,000 wild barn owls from Switzerland to investigate the presence, severity, and genetic architecture of inbreeding depression in three morphological traits. Using a combination of linear models (accounting for age) and non-linear models (to measure growth effects) we clearly show inbreeding depression is present in this population. Moreover, by breaking-down the timing of the effects we also have a better ability to detect inbreeding depression, as in some traits we find that it manifests during juvenile growth, and in others during adulthood. To our knowledge this is the first study to show direct evidence for inbreeding depression during the crucial early life weight gain period in a wild animal. We further show that certain trait-specific patterns may reflect differences in environmental influences across life stages, as we find that heritability is often lower before adulthood. We also use two classes of genomic inbreeding coefficients: F ROH and F UniW, and while the directionality of effects is equivalent, the strength of evidence regarding the presence of inbreeding depression differs depending on the coefficient used. This discrepancy might give some insight into the frequency distribution of responsible variants, as each coefficient weights variants differently based on their population frequencies. Finally, an assessment of local genomic inbreeding effects highlights a handful of regions with significantly deleterious effects, alongside many regions with a smaller contribution to the observed inbreeding depression. Overall, we provide a comprehensive overview of the effects of inbreeding in this wild population, highlighting the dynamic interplay between environmental influences and the selection pressure against inbred individuals. ### Competing Interest Statement The authors have declared no competing interest. Swiss National Science Foundation, 310030_215709

Mercury (Hg) accumulation and biomagnification in the barn owl (Tyto alba) food chain were investigated using bioindicator samples from three trophic levels: (1) soil and moss (atmospheric deposition indicators), (2) small mammal fur from regurgitated pellets (herbivores and omnivores), and (3) barn owl down feathers (apex predators). Spatial analysis identified regional Hg variation in soil, fur and feathers. Statistical models explored the effects of proximity to water bodies, wetlands and nearby pollution sources. The highest total Hg (THg) concentrations were found in feathers (170 ± 160 µg kg-1, n = 246) and fur in regurgitated pellets (150 ± 200 µg kg-1, n = 150), followed by soil (63 ± 17 µg kg-1, n = 63). Bioaccumulation factors were 2.3 (soil to fur) and 2.7 (soil to feather). Biomagnification factor from fur to feathers was 1.8. Methyl Hg (MeHg), measured in a subset of samples, was 120 ± 130 µg kg-1 in fur (n = 29) and 150 ± 98 µg kg-1 in feathers (n = 42), with 75-97 % of THg in feathers as MeHg. Prey composition significantly influenced fur THg levels, with higher concentrations in diets with omnivorous prey (Apodemus flavicollis) compared to herbivorous prey (Microtus arvalis). These findings highlight the importance of diet in Hg monitoring and biomagnification studies.

Regulation of melanin-based pigmentation is complex, involving multiple genes. Because different genes can contribute to the same pigmentation phenotype, the genes identified in model organisms may not necessarily apply to wild species. In the barn owl (Tyto alba), ventral plumage colour ranges from white to rufous, with genetic variation in the melanocortin 1 receptor gene (MC1R) accounting for at least a third of this variation. In the present study, we used transcriptomic data to compare the gene expression profiles of growing feathers from nestlings with different MC1R genotypes. We identified 21 differentially expressed genes, nine of which are involved in melanogenesis, while seven are related to neurotransmitter function or synaptic activity. With the exception of CALB1, all of the differentially expressed genes were upregulated in rufous owls compared to white barn owls. To the best of our knowledge, this study is the first to link melanin production with neurotransmitter-related genes, and we discuss possible evolutionary explanations for this connection.

Parental cooperation in species with extended biparental care is essential for offspring survival, yet real-time negotiation and coordination in the wild remain poorly understood. We simultaneously Global Positioning System (GPS)- and accelerometer-tracked 68 breeding pairs of barn owls (Tyto alba) during chick rearing, quantifying parents' hunting effort, prey deliveries, self-feeding, nest attendance, and partner encounters. Within pairs, parental investment was highly plastic, with low repeatability of nightly provisioning shares. Females increased provisioning when males underperformed or when foraging habitat was likely poor. Parents synchronized foraging schedules and nest visits, exhibiting turn-taking-like coordination; pairs that shared provisioning more equally foraged in parallel overnight and met frequently at the nest. We detected sequential, between-night adjustments, whereby effort on one night influenced provisioning the next. Pairs maintaining more equitable care achieved higher survival and growth in their later-hatching nestlings. Our findings demonstrate how high-resolution biologging reveals dynamic behavioral mechanisms underpinning flexible biparental care under ecological variability.

Understanding how wild populations adapt to rapid environmental change requires linking phenotypic evolution to its genomic basis over contemporary timescales. This remains challenging because genetic and environmental effects are often intertwined. Here, we leverage a 30-year study of Swiss barn owls (Tyto alba) to explore this process. During this period, owls have evolved darker plumage and increased spottiness, two melanin-based traits associated with fitness. Whole-genome sequencing of 3,102 individuals reveals that these traits are largely controlled by few loci of major effect with partially overlapping architectures. Temporal allele frequency analyses show subtle but consistent shifts at these loci. Simulations indicate that genetic drift alone cannot explain these changes, whereas models incorporating selection do. Our findings demonstrate that selection on a small number of loci can drive rapid phenotypic evolution in the wild. This work underscores the adaptive potential of natural populations and the value of long-term genomic monitoring under accelerating climate change. ### Competing Interest Statement The authors have declared no competing interest. Swiss National Science Foundation, https://ror.org/00yjd3n13, 31003A_173178, 310030_200321/1, ICC00I0-23168, 31003A_173178, 31003A_179358, 310030_215709

Investigating among-individual differences in reproductive success and survival is essential for understanding eco-evolutionary processes. We used 5 years of demographic data from 556 breeding barn owls (Tyto alba) to estimate associations between intrinsic and extrinsic covariates on survival and reproduction throughout the annual cycle. As males and females have distinct roles in reproduction, environmental conditions and individual quality may be differentially linked to their fitness at different time points. Males breeding early and inhabiting prey-rich areas experienced higher reproductive success but faced greater reproductive costs. Indeed, the number of offspring a male cared for was negatively associated with his body condition and survival. However, our results indicate that these influences can be mitigated in males experiencing favourable post-breeding environmental conditions. For female owls, early breeding and high food availability during the breeding period were linked with increased reproductive success. Prey availability during incubation and higher reproductive output were associated with higher survival into the next breeding period in females. Unlike males, females did not exhibit obvious trade-offs between reproductive success and survival. Our research demonstrates trade-offs between fecundity and survival, and that females paired with males able to provide sufficient food experience higher survival and reproduction.