Hearing Assessment of Free-Ranging Owls and Implications for Wildlife Rehabilitation: 31 Cases (2014-2023).

Owls, members of the avian order Strigiformes, are nocturnal birds of prey that are found worldwide except for Antarctica. Traumatized, free-ranging owls are commonly presented to veterinary hospitals and wildlife rehabilitation facilities with the goal of providing medical care and rehabilitation to enable release back into their natural habitat. Minimal guidelines exist for the release of wildlife, and whereas a need for functional vision is described in raptors, assessing and evaluating hearing is usually not mentioned. This can be problematic for nocturnal predators because hearing is the primary sense utilized by owls when hunting and navigating in their dark environment. The brainstem auditory evoked response (BAER) test is a minimally invasive, objective assessment of hearing commonly used in companion animals. To the authors' knowledge, routine or standardized BAER evaluation has not been reported in traumatized, free-ranging owls. In the following retrospective study, 31 free-ranging owls presented to the University of Georgia Veterinary Teaching Hospital for known or suspected trauma or being found in a debilitated state underwent BAER testing to assess for the presence of complete sensorineural hearing loss. Similar to assessment of hearing in companion animals, the BAER test was elicited using a broad click stimulus delivered at 85 dB nHL. In all owls, qualitative assessment and peak latency measurements of the BAER test reflected hearing ability. This study highlights the importance of hearing in nocturnal raptors, how BAER testing can aid in decision making regarding rehabilitation, and provides a foundation for further investigation of hearing loss in traumatized owls. We suggest that veterinarians working with free-ranging owls in a rehabilitation setting should consider BAER testing as part of routine diagnostic testing.

The Neural Representation of Binaural Sound Localization Cues Across Different Subregions of the Chicken's Inferior Colliculus.

The sound localization behavior of the nocturnally hunting barn owl and its underlying neural computations is a textbook example of neuroethology. Differences in sound timing and level at the two ears are integrated in a series of well-characterized steps, from brainstem to inferior colliculus (IC), resulting in a topographical neural representation of auditory space. It remains an important question of brain evolution: How is this specialized case derived from a more plesiomorphic pattern? The present study is the first to match physiology and anatomical subregions in the non-owl avian IC. Single-unit responses in the chicken IC were tested for selectivity to different frequencies and to the binaural difference cues. Their anatomical origin was reconstructed with the help of electrolytic lesions and immunohistochemical identification of different subregions of the IC, based on previous characterizations in owl and chicken. In contrast to barn owl, there was no distinct differentiation of responses in the different subregions. We found neural topographies for both binaural cues but no evidence for a coherent representation of auditory space. The results are consistent with previous work in pigeon IC and chicken higher-order midbrain and suggest a plesiomorphic condition of multisensory integration in the midbrain that is dominated by lateral panoramic vision.

Comparison three primer pairs for molecular sex determination in Eurasian pygmy owls (Glaucidium passerinum).

Bird sex determination is fundamental in various ecological and biological studies, although many avian species cannot be sexed visually due to their monomorphic and/or monochromatic appearance. Thus, reliable laboratory methods for sexing are a prerequisite. Most avian nestlings lack sex-related signs, including the Eurasian pygmy owl (Glaucidium passerinum). We performed laboratory sex determination analysis of this species using blood samples of 242 juveniles and nine adults. It relied on the qPCR of the specific intron from the chromo-helicase DNA-binding protein 1 gene. We tested three primer sets, the P2/P8, 2550F/2718R, and CHD1F/CHD1R, commonly used for bird laboratory sexing. The outcomes were displayed on an agarose gel electrophoresis and a plot from melt curve analysis, which had not been previously conducted in Eurasian pygmy owls. We found that only primer set CHD1F/CHD1R proved reliable, as the only one determined sex with one and two band/s and peak/s on the electrophoresis and the melt curve plot for males and females, respectively. The other two primer pairs failed and depicted one band/peak in all specimens regardless of their sex. Therefore, we recommend performing Eurasian pygmy owls' laboratory sexing by qPCR with CHD1F/CHD1R primers only.

Leucocytozoon Infection Does Not Influence the Survival of Boreal Owl Aegolius funereus Nestlings.

Leucocytozoon infection has been observed to impact the reproductive ecology and physiology of avian hosts, but its influence on nestling survival remains unclear. We investigated the effect of Leucocytozoon infection intensity, determined through triplicate PCR sample analyses, on the survival of 256 boreal owl (Aegolius funereus) nestlings during an 8-yr study. Contrary to our expectations, the survival probability of boreal owl nestlings was not influenced by their Leucocytozoon infection intensity. Nestling age and Leucocytozoon infection intensity in male and female parents also did not impact nestling survival. Instead, food abundance and hatching order were the key factors influencing nestling survival. Additionally, we observed a significantly higher Leucocytozoon infection intensity in male parents compared to female parents and nestlings. We suggest a distinct division of parental roles may lead females and nestlings staying within the nest boxes (cavities) to experience lower exposure to potential vectors transmitting blood parasites than their male counterparts. Our study shows that Leucocytozoon disease may not be lethal for boreal owl chicks, exhibiting a below-average infection intensity compared to their male parents.

La infección por Leucocytozoon no influye en la supervivencia de los polluelos de mochuelo boreal Aegolius funereus. Se ha observado que la infección por Leucocytozoon afecta la ecología y fisiología reproductiva de las aves hospedadoras, pero su influencia en la supervivencia de los polluelos aún no está completamente determinada. Se investigó el efecto de la intensidad de la infección por Leucocytozoon, determinada mediante análisis de muestras de PCR por triplicado, sobre la supervivencia de 256 polluelos de mochuelo boreal (Aegolius funereus) durante un estudio de ocho años. Contrariamente a nuestras expectativas, la probabilidad de supervivencia de los polluelos de mochuelo boreal no se vio influenciada por la intensidad de la infección por Leucocytozoon. La edad de los polluelos y la intensidad de la infección por Leucocytozoon en los padres machos y hembras tampoco afectaron la supervivencia de los polluelos. En cambio, la abundancia de alimento y el orden de eclosión fueron los principales factores que influyeron en la supervivencia de los polluelos. Además, se observó una intensidad de infección por Leucocytozoon significativamente mayor en los padres machos en comparación con las hembras y los polluelos. Se sugiere que una clara división de los roles parentales puede llevar a que las hembras y los polluelos que permanecen dentro de las cajas nido (cavidades) experimenten una menor exposición a vectores potenciales que transmitan parásitos sanguíneos en comparación con los individuos adultos masculinos. Nuestro estudio muestra que la enfermedad de Leucocytozoon puede no ser letal para los polluelos de mochuelo boreal, ya que exhiben una intensidad de infección por debajo del promedio en comparación con sus padres machos.

Single trial Bayesian inference by population vector readout in the barn owl's sound localization system.

Bayesian models have proven effective in characterizing perception, behavior, and neural encoding across diverse species and systems. The neural implementation of Bayesian inference in the barn owl's sound localization system and behavior has been previously explained by a non-uniform population code model. This model specifies the neural population activity pattern required for a population vector readout to match the optimal Bayesian estimate. While prior analyses focused on trial-averaged comparisons of model predictions with behavior and single-neuron responses, it remains unknown whether this model can accurately approximate Bayesian inference on single trials under varying sensory reliability, a fundamental condition for natural perception and behavior. In this study, we utilized mathematical analysis and simulations to demonstrate that decoding a non-uniform population code via a population vector readout approximates the Bayesian estimate on single trials for varying sensory reliabilities. Our findings provide additional support for the non-uniform population code model as a viable explanation for the barn owl's sound localization pathway and behavior.

Towards silent and efficient flight by combining bioinspired owl feather serrations with cicada wing geometry.

As natural predators, owls fly with astonishing stealth due to the serrated feather morphology that produces advantageous flow characteristics. Traditionally, these serrations are tailored for airfoil edges with simple two-dimensional patterns, limiting their effect on noise reduction while negotiating tradeoffs in aerodynamic performance. Conversely, the intricately structured wings of cicadas have evolved for effective flapping, presenting a potential blueprint for alleviating these aerodynamic limitations. In this study, we formulate a synergistic design strategy that harmonizes noise suppression with aerodynamic efficiency by integrating the geometrical attributes of owl feathers and cicada forewings, culminating in a three-dimensional sinusoidal serration propeller topology that facilitates both silent and efficient flight. Experimental results show that our design yields a reduction in overall sound pressure levels by up to 5.5 dB and an increase in propulsive efficiency by over 20% compared to the current industry benchmark. Computational fluid dynamics simulations validate the efficacy of the bioinspired design in augmenting surface vorticity and suppressing noise generation across various flow regimes. This topology can advance the multifunctionality of aerodynamic surfaces for the development of quieter and more energy-saving aerial vehicles.

The missing toxic link: Exposure of non-target native marsupials to second-generation anticoagulant rodenticides (SGARs) suggest a potential route of transfer into apex predators.

Anticoagulant rodenticides (ARs) are used globally to control rodent pests. Second-generation anticoagulant rodenticides (SGARs) persist in the liver and pose a significant risk of bioaccumulation and secondary poisoning in predators, including species that do not generally consume rodents. As such, there is a clear need to understand the consumption of ARs, particularly SGARs, by non-target consumers to determine the movement of these anticoagulants through ecosystems. We collected and analysed the livers from deceased common brushtail possums (Trichosurus vulpecula) and common ringtail possums (Pseudocheirus peregrinus), native Australian marsupials that constitute the main diet of the powerful owl (Ninox strenua), an Australian apex predator significantly exposed to SGAR poisoning. ARs were detected in 91 % of brushtail possums and 40 % of ringtail possums. Most of the detections were attributed to SGARs, while first-generation anticoagulant rodenticides (FGARs) were rarely detected. SGAR concentrations were likely lethal or toxic in 42 % of brushtail possums and 4 % of ringtail possums with no effect of age, sex, or weight detected in either species. There was also no effect of the landscape type possums were from, suggesting SGAR exposure is ubiquitous across landscapes. The rate of exposure detected in these possums provides insight into the pathway through which ARs are transferred to one of their key predators, the powerful owl. With SGARs entering food-webs through non-target species, the potential for bioaccumulation and broader secondary poisoning of predators is significantly greater and highlights an urgent need for routine rodenticide testing in non-target consumers that present as ill or found deceased. To limit their impact on ecosystem stability the use of SGARs should be significantly regulated by governing agencies.

Microplastic in an apex predator: evidence from Barn owl (Tyto alba) pellets in two sites with different levels of anthropization.

Plastic pollution in terrestrial and freshwater environments and its accumulation along food chains has been poorly studied in birds. The Barn owl (Tyto alba) is an opportunistic and nocturnal apex predator feeding mostly on small mammals. In this note, we reported evidence of microplastics (MPs) contamination in Barn owl pellets collected, for the first time, in two sites with different levels of anthropization (low: natural landscape mosaic vs. high extensive croplands). The following polymers have been recorded: polyvinylchloride (PVC), polyethylene (PE), expanded polyester (EPS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyester (PL), viscose, and starch-based biopolymer. We found significant higher MPs frequency in the most anthropized site. Our results suggest that pellet' analysis may represent a cost-effective method for monitoring MP contamination along food chains in terrestrial ecosystems.

Auditory Competition and Coding of Relative Stimulus Strength across Midbrain Space Maps of Barn Owls.

The natural environment challenges the brain to prioritize the processing of salient stimuli. The barn owl, a sound localization specialist, exhibits a circuit called the midbrain stimulus selection network, dedicated to representing locations of the most salient stimulus in circumstances of concurrent stimuli. Previous competition studies using unimodal (visual) and bimodal (visual and auditory) stimuli have shown that relative strength is encoded in spike response rates. However, open questions remain concerning auditory-auditory competition on coding. To this end, we present diverse auditory competitors (concurrent flat noise and amplitude-modulated noise) and record neural responses of awake barn owls of both sexes in subsequent midbrain space maps, the external nucleus of the inferior colliculus (ICx) and optic tectum (OT). While both ICx and OT exhibit a topographic map of auditory space, OT also integrates visual input and is part of the global-inhibitory midbrain stimulus selection network. Through comparative investigation of these regions, we show that while increasing strength of a competitor sound decreases spike response rates of spatially distant neurons in both regions, relative strength determines spike train synchrony of nearby units only in the OT. Furthermore, changes in synchrony by sound competition in the OT are correlated to gamma range oscillations of local field potentials associated with input from the midbrain stimulus selection network. The results of this investigation suggest that modulations in spiking synchrony between units by gamma oscillations are an emergent coding scheme representing relative strength of concurrent stimuli, which may have relevant implications for downstream readout.

Diversity, richness, and evenness of birds in Rana Resort Forest, District Kasur, Punjab, Pakistan.

This research was carried out to determine avian diversity in the Rana Resort Forest from June to August 2023. A total of 655 birds were observed; these birds belonged to 36 different species from 11 orders; 27 families and 36 genera were found in the forest. The observed avian species that belong to the Muscicapidae family had the highest number of species, while Strigidae had the lowest number of species. The highest numbers of the order Passeriformes were recorded. Among the bird species observed, 33 were residents, 1 was a winter visitor, and 2 were summer breeders. The species diversity, richness, and evenness indices are 3.5238, 5.3973, and 0.10492, respectively. According to the index results, the Rana Resort Forest is a diverse area, but the species are not evenly distributed due to some of the threats observed during the study, such as habitat destruction, poverty, and unawareness.

Shoulder viscoelasticity in a raptor-inspired model alleviates instability and enhances passive gust rejection.

Recent experiments with gliding raptors reveal a perplexing dichotomy: remarkably resilient gust rejection, but, at the same time, an exceptionally high degree of longitudinal instability. To resolve this incompatibility, a multiple degree of freedom model is developed with minimal requisite complexity to examine the hypothesis that the bird shoulder joint may embed essential stabilizing and preflexive mechanisms for rejecting rapid perturbations while simplifying and reducing control effort. Thus, the formulation herein is centrally premised upon distinct wing pitch and body pitch angles coupled via a Kelvin-Voigt viscoelastic shoulder joint. The model accurately exhibits empirical gust response of an unstable gliding raptor, generates biologically plausible equilibrium configurations, and the viscoelastic shoulder coupling is shown to drastically alleviate the high degree of instability predicted by conventional linear flight dynamics models. In fact, stability analysis of the model predicts a critical system timescale (the time to double amplitude of a pitch divergence mode) that is commensurate within vivomeasured latency of barn owls (Tyto alba). Active gust mitigation is studied by presupposing the owl behaves as an optimal controller. The system is under-actuated and the feedback control law is resolved in the controllable subspace using a Kalman decomposition. Importantly, control-theoretic analysis precisely identifies what discrete gust frequencies may be rapidly and passively rejected versus disturbances requiring feedback control intervention.

Interaction of barn owl leading edge serrations with freestream turbulence.

The silent flight of barn owls is associated with wing and feather specialisations. Three special features are known: a serrated leading edge that is formed by free-standing barb tips which appears as a comb-like structure, a soft dorsal surface, and a fringed trailing edge. We used a model of the leading edge comb with 3D-curved serrations that was designed based on 3D micro-scans of rows of barbs from selected barn-owl feathers. The interaction of the flow with the serrations was measured with Particle-Image-Velocimetry in a flow channel at uniform steady inflow and was compared to the situation of inflow with freestream turbulence, generated from the turbulent wake of a cylinder placed upstream. In steady uniform flow, the serrations caused regular velocity streaks and a flow turning effect. When vortices of different size impacted the serrations, the serrations reduced the flow fluctuations downstream in each case, exemplified by a decreased root-mean-square value of the fluctuations in the wake of the serrations. This attenuation effect was stronger for the spanwise velocity component, leading to an overall flow homogenization. Our findings suggest that the serrations of the barn owl provide a passive flow control leading to reduced leading-edge noise when flying in turbulent environments.

The red listed eagle owl (Bubo bubo) population in Norway is exposed to POP levels exceeding threshold values for adverse health effects.

The eagle owl (Bubo bubo) population in Norway is today classified as critically endangered on the red list of endangered species. Because previous studies have detected high concentrations of Persistent Organic Pollutants (POPs) in birds of prey, concerns have been raised whether POPs exposure are a significant factor to the substantial decline of the eagle owl population. The aims of this study were to measure the levels of POPs in eagle owls and to assess whether POPs may represent a potential health risk. POPs were analysed in liver samples from 100 eagle owls collected between 1994 and 2014. The concentrations of POPs were generally very high and individual birds had levels among the highest measured worldwide. The contaminant groups analysed were highly correlated (p < 0.0001). The concentrations of sum of Polychlorinated Biphenyls (∑PCB) exceeded the threshold value from moderate to severe health risk in 90% of the birds. The birds with cachectic or lean body condition had significantly higher levels of contaminants than those with higher body condition scores. No significant temporal or spatial trends were noted. The lack of temporal trends, suggest that the downward trend of POPs, appear to be levelling off. The lack of differences between inland and coastal regions suggest that the risk of exposure may be comparable between predatory birds feeding in marine or terrestrial food webs. The significantly higher POPs levels detected in individuals with poor body condition may be due to reduced fat stores and thereby higher concentration in the remaining fat and/or the weight loss could be induced by toxic effects. The high proportion of birds exceeding the threshold values for severe and high risk of adverse effects, suggest that the high contamination load may reduce the eagle owl's fitness and survival and, thus, contribute to decline of the eagle owl population.

Are owls technically capable of making a full head turn?

The three-dimensional configuration of the neck that produces extreme head turn in owls was studied using the Joint Coordinate System. The limits of planar axial rotation (AR), lateral, and sagittal bending in each vertebral joint were measured. They are not extraordinary among birds, except probably for the extended ability for AR. The vertebral joint angles involved in the 360° head turn do not generally exceed the limits of planar mobility. Rotation in one plane does not expand the range of motion in the other, with one probable exception being extended dorsal bending in the middle of the neck. Therefore, the extreme 360° head turn can be presented as a simple combination of the three planar motions in the neck joints. Surprisingly, certain joints are always laterally bent or axially rotated to the opposite side than the head was turned. This allows keeping the anterior part of the neck parallel to the thoracic spine, which probably helps preserve the ability for peering head motions throughout the full head turn. The potential ability of one-joint muscles of the owl neck, the mm. intertransversarii, to ensure the 360° head turn was addressed. It was shown that the 360° head turn does not require these muscles to shorten beyond the known contraction limit of striated vertebrate muscles. Shortening by 50% or less is enough for the mm. intertransversarii in the middle neck region for the 360° head turn. This study has broad implications for further research on vertebral mobility and function in a variety of tetrapods, providing a new method for CT scan-based measurement of intervertebral angles.

Platynosomum (Trematoda: Dicrocoeliidae) infection in barn owls (Tyto alba) in Northeastern Brazil.

Platynosomum spp. are parasites that inhabit the gallbladder and bile ducts of various mammals and birds worldwide. Most studies of Platynosomum spp. in birds focus on the observation and morphological characterization of the parasite through parasitological or molecular examinations, with scarce literature describing anatomopathological alterations, mainly histopathological. We report the case of a male barn owl infected with Platynosomum spp.. At necropsy, the barn owl showed dilation with parasites and fibrosis of the intrahepatic bile ducts and gallbladder. Microscopically, it was possible to identify trematodes in the bile ducts associated with a lymphoplasmacytic inflammatory infiltrate. The morphological structures of the worms were described on histopathology and direct examination. The presence of parasitism that is usually cosmopolitan in wild animals represents a risk to the biodiversity of fauna in the region, as well as a warning about the spread and maintenance of the biological cycle of the worm in humans and domestic animals.

Active monitoring of long-eared owl (Asio otus) nestlings reveals widespread exposure to anticoagulant rodenticides across different agricultural landscapes.

The widespread use of anticoagulant rodenticides (ARs) poses a worldwide threat to farmland wildlife. These compounds accumulate in tissues of both target and non-target species, potentially endangering both direct consumers and their predators. However, investigations on ARs in blood of free-ranging predatory birds are rare. Here, the long-eared owl (Asio otus) has been used as a model predator to assess AR exposure in different agricultural landscapes from a Mediterranean semiarid region. A total of 69 owlets from 38 nests were blood-sampled over 2021 and 2022, aiming to detect AR residues and explore factors that determine their exposure, such as land uses. In addition, prothrombin time (PT) test was conducted to assess potential effects of AR contamination. Overall, nearly all the samples (98.6 %) tested positive for at least one compound and multiple ARs were found in most of the individuals (82.6 %). Among the ARs detected, flocoumafen was the most common compound (88.4 % of the samples). AR total concentration (ΣARs) in blood ranged from 0.06 to 34.18 ng mL-1, detecting the highest levels in the most intensively cultivated area. The analysis of owl pellets from 19 breeding territories showed relevant among-site differences in the contribution of rodents and birds into the diet of long-eared owls, supporting its high dietary plasticity and indicating AR presence at multiple trophic levels. Moreover, a positive and significant correlation was found between ΣARs and PT (Rho = 0.547, p < 0.001), which demonstrates the direct effect of ARs on free-living nestlings. Our results provide a preliminary overview of AR exposure in a little-studied owl species inhabiting agricultural and rural landscapes. Despite the low detected levels, these findings indicate widespread exposure -often to multiple compounds- from early life stages, which raises concern and draws attention to an ongoing and unresolved contamination issue.

Molecular Survey of Haemosporidian Parasites in Procellariiformes Sampled in Southern Brazil, 2013-22.

The order Procellariiformes includes several species of seabirds that perform long-distance migrations crossing all the oceans. These movements may contribute to the dispersal and exchange of hemoparasites, such as haemosporidians. There is a lack of studies regarding the order Haemosporida in Procellariiformes, and, to date, only the genus Plasmodium has been reported. This survey investigated the occurrence of the three genera of haemosporidians, Plasmodium, Haemoproteus, and Leucocytozoon, in samples collected between 2013 and 2022 from 95 individuals of 14 species of Procellariiformes from southern Brazil, including live animals in rehabilitation centers, individuals caught as incidental bycatch, and carcasses found along the coast. A total of 171 samples of blood and fragments of liver and spleen were analyzed, with extracted DNA being subjected to a nested PCR followed by phylogeny analysis. All animals were negative for Plasmodium spp. and Leucocytozoon spp., but one Black-browed Albatross (Thalassarche melanophris) and one Manx Shearwater (Puffinus puffinus) specimen were positive for Haemoproteus spp. The sequences obtained from positive seabirds did not show 100% similarity with other known lineages available in the MalAvi database and thus were probably novel lineages. However, one sequence clustered together with Haemoproteus noctuae, a parasite from Strigiformes, while the other was grouped with Haemoproteus columbae, which is classically related to Columbiformes. These results suggest that both positive animals may have become infected when beached or in rehabilitation centers by a spillover of vectors from local birds. This highlights the importance of surveillance of the health of Procellariiformes regarding the possibility of dissemination of new pathogens in different bird populations.

Barn owls specialized sound-driven behavior: Lessons in optimal processing and coding by the auditory system.

The barn owl, a nocturnal raptor with remarkably efficient prey-capturing abilities, has been one of the initial animal models used for research of brain mechanisms underlying sound localization. Some seminal findings made from their specialized sound localizing auditory system include discoveries of a midbrain map of auditory space, mechanisms towards spatial cue detection underlying sound-driven orienting behavior, and circuit level changes supporting development and experience-dependent plasticity. These findings have explained properties of vital hearing functions and inspired theories in spatial hearing that extend across diverse animal species, thereby cementing the barn owl's legacy as a powerful experimental system for elucidating fundamental brain mechanisms. This concise review will provide an overview of the insights from which the barn owl model system has exemplified the strength of investigating diversity and similarity of brain mechanisms across species. First, we discuss some of the key findings in the specialized system of the barn owl that elucidated brain mechanisms toward detection of auditory cues for spatial hearing. Then we examine how the barn owl has validated mathematical computations and theories underlying optimal hearing across species. And lastly, we conclude with how the barn owl has advanced investigations toward developmental and experience dependent plasticity in sound localization, as well as avenues for future research investigations towards bridging commonalities across species. Analogous to the informative power of Astrophysics for understanding nature through diverse exploration of planets, stars, and galaxies across the universe, miscellaneous research across different animal species pursues broad understanding of natural brain mechanisms and behavior.

Characterization of the diversity of barn owl's mitochondrial genome reveals high copy number variations in the control region.

Mitochondria are known to play an essential role in the cell. These organelles contain their own DNA, which is divided in a coding and non-coding region (NCR). While much of the NCR's function is unknown, tandem repeats have been observed in several vertebrates, with extreme intra-individual, intraspecific and interspecific variation. Taking advantage of a new complete reference for the mitochondrial genome of the Afro-European Barn Owl (Tyto alba), as well as 172 whole genome-resequencing; we (i) describe the reference mitochondrial genome with a special focus on the repeats in the NCR, (ii) quantify the variation in number of copies between individuals, and (iii) explore the possible factors associated with the variation in the number of repetitions. The reference mitochondrial genome revealed a long (256bp) and a short (80bp) tandem repeat in the NCR region. The re-sequenced genomes showed a great variation in number of copies between individuals, with 4 to 38 copies of the Long and 6 to 135 copies of the short repeat. Among the factors associated with this variation between individuals, the tissue used for extraction was the most significant. The exact mechanisms of the formations of these repeats are still to be discovered and understanding them will help explain the maintenance of the polymorphism in the number of copies, as well as their interactions with the metabolism, the aging and health of the individuals.

The genomic architecture of continuous plumage colour variation in the European barn owl (Tyto alba).

The maintenance of colour variation in wild populations has long fascinated evolutionary biologists, although most studies have focused on discrete traits exhibiting rather simple inheritance patterns and genetic architectures. However, the study of continuous colour traits and their potentially oligo- or polygenic genetic bases remains rare in wild populations. We studied the genetics of the continuously varying white-to-rufous plumage coloration of the European barn owl (Tyto alba) using a genome-wide association approach on the whole-genome data of 75 individuals. We confirmed a mutation at the melanocortin-1-receptor gene (MC1R) is involved in the coloration and identified two new regions, located in super-scaffolds 9 and 42. The combination of the three regions explains most of the colour variation (80.37%, 95% credible interval 58.45-100%). One discovered region, located in the sex chromosome, differs between the most extreme colorations in owls sharing a specific MC1R genotype. This region may play a role in the colour sex dimorphism of this species, possibly in interaction with the autosomal MC1R. We thus provide insights into the genetic architecture of continuous colour variation, pointing to an oligogenic basis with potential epistatic effects among loci that should aid future studies understanding how continuous colour variation is maintained in nature.