Asio Otus Research Articles

LWS visual pigment in owls: Spectral tuning inferred by genetics

Owls constitute a diverse group of raptors, active at different times of the day with distinct light conditions that might be associated with multiple visual adaptations. We investigated whether shifts in the spectral sensitivity of the L cone visual pigment, as inferred by analysis of gene structure, could be one such adaptive mechanism. Using Sanger sequencing approach, we characterized the long wavelength-sensitive (LWS) opsin gene expressed in the retina of five owl species, specifically chosen to represent distinct patterns of activity. Nocturnality was epitomized by the American barn owl (Tyto furcata), the striped owl (Asio clamator), and the tropical screech owl (Megascops choliba); diurnality, by the ferruginous pygmy owl (Glaucudium brasilianum); and cathemerality, by the burrowing owl (Athene cunicularia). We also analyzed the presence of the L cone in the retinas of four species of owl (T. furcata, A. cunicularia, G. brasilianum and M. choliba) using immnunohistochemistry. Five critical sites for the spectral tuning of the LWS opsin (164, 181, 261, 269, and 292) were analyzed and compared to the sequence of other birds. The sequence of A. cunicularia showed a substitution on residue 269, with the presence of an alanine instead threonine, which generates an estimated maximum absorption (λmax) around 537 nm. No other variation was found in the spectral tuning sites of the LWS opsin, among the other species, and the λmax was estimated at around 555 nm. The presence of L cones in the retinas of the four species of owls was revealed using immunohistochemistry and we observed a reduced number of L cones in T. furcata compared to A. cunicularia, G. brasilianum and M. choliba.

Selection of prey by size and sex in the Long-eared Owl Asio otus

ABSTRACTCapsule: Voles predated by Long-eared Owls Asio otus were more likely to be female and smaller than the voles in the available population.Aims: Our study aimed to estimate the size and sex of prey in the diet of Long-eared Owls and compare them with the size and sex of prey in the field.Methods: The study was carried out in 2016 and 2017 at Moscow Region, Russia. Prey remains were extracted from pellets produced by Long-eared Owls. The sex of prey was identifiable due to sexual dimorphism of pelvic bones, and bone dimensions were used to estimate the body mass of prey. Small mammals were also trapped in the study area to compare the sex and size of animals taken as prey with those in the general population.Results: Long-eared Owls did not capture small mammals randomly with respect to size and sex. In general, individuals of the two main prey species in the pellets of Long-eared Owls were significantly smaller than the trapped animals. Long-eared Owls more often caught the females of both species of voles. However, the percentages of females in the diet varied between years.Conclusions: Long-eared Owls more often catch individual voles of a certain size and sex. We suggest that this selective predation could influence not only the number of prey species, but could also impact the structure of their local populations.

Investigation on Diet of Long-Eared Owl (Asio Otus) Inhabiting Fatih Natural Park (Turkey)

Pellet analyses were used to identify small mammal species in the diet of this owl species in order to reveal its ecological role. In this study, 706 pellets of Asio otus were collected from 3 different localities in Fatih Natural Park between February and March 2014. Pellets were dissolved by using 3% NaOH solution and then bones were dehydrated and identified. The aim of this study was to determine mammal composition in the diet of Asio otus inhabiting Fatih Natural Park of Yozgat Province, Turkey. Residues of bone from 1293 individuals/preys corresponding to 42377.41 g biomass in total were detected as the result of analysis. These individuals were identified to belonging to 12 mammal species ( Crocidura suaveolens , Suncus etruscus , Microtus hartingi/lydius , Microtus levis , Microtus sp., Cricetulus migratorius , Mesocricetus brandti , Apodemus sp., Apodemus sylvaticus , Apodemus whitherbyi , Mus macedonicus , and Meriones tristrami ) from 3 families and 8 genera. Microtus hartingi/lydius, which is known as agricultural pest, was dominant in the diet of Asio otus . When diversity of mammal species within the food composition was examined, Asio otus nesting in forest was found to primarily prefer agricultural and steppe areas, and was also found in woody and bushy areas. The use of Asio otus can be taken into consideration when dealing with rodent species known as agricultural pests.

A method designed for bionic air bearing based on the structure of long-eared owl wing

PurposeThe purpose of this paper is to design a kind of air bearing which is based on bionics. Compare with ordinary air bearing, the air pressure consumption is reduced and energy is saved.Design/methodology/approachThis paper puts forward a proposition that a bionic bearing structure is designed based on the bionics principle. First, the authors analyze the microstructure of the wings of long-eared owls and the structural mapping model is established. Second, the theoretical formula is derived through the model, and the structural parameters are optimized by sequence quadratic program (SQP). Lastly, the experimental model is made by 3D printing technology, and the experimental data are analyzed to verify the feasibility of the theory.FindingsBy comparing the experimental data, it can be seen that the air pressure of the original air bearing is reduced by 27 per cent, and the validity of the theory and design method is verified.Originality/valueIn this paper, a design method of air bearing based on bionic principle is presented, which can save the air pressure required for working of air bearing, and the structure of air bearing is expected to be applied in engineering.

Use of corvids’ nests by other bird species in Baikal Siberia and Mongolia

The paper presents the species composition of corvids in Baikal Siberia and Mongolia. More than 700 nests of 8 species of corvids in Transbaikalia, Baikal and Mongolia were examined. 133 cases of using nests of 5 species of corvids (Magpies, Eastern Carrion Crow, Rooks and Daurian Jackdaws) by other species of birds were noted. Nests of small corvids do not attract other birds. Nests of magpies are most commonly used; they are characterized by a specific structure. Of the 8 species that use corvid nests for nesting, Amur red-footed Falcon and long-eared owl are obligate tenants. Then goes Kestrel that prefers magpie nests. The number of these types in many places is determined by the abundance of magpies and crows. In recent years, due to the high number of magpies, the number of Amur falcons in the region is growing. They began following magpies to penetrate the outskirts of Ulan-Ude. Three species (Mallard, hobby, tree sparrows) are considered optional to be the tenants and three other species (Ruddy Shelduck, Long-eared Owl and House Sparrow) are considered to be random. Tree sparrows often nest in the magpie nests in natural habitats. Almost all types of tenants use old nests of the owners. Regional features in the use of corvid nests are revealed. Some species in different regions do not prefer the same nests of different types of corvids.

Infestation parameters for chewing lice (Phthiraptera: Amblycera, Ischnocera) infesting owls (Aves: Strigidae, Tytonidae) in Manitoba, Canada

AbstractEleven of the 12 species of owls (Aves: Strigidae, Tytonidae) known to occur in Manitoba, Canada, were examined for chewing lice (Phthiraptera: Amblycera, Ischnocera) from 1976 to 2015: barn owl (Tyto alba(Scopoli); Aves: Tytonidae) (n= 2), snowy owl (Bubo scandiacus(Linnaeus); Aves: Strigidae) (n= 77), great horned owl (Bubo virginianus(Gmelin); Aves: Strigidae) (n= 262), great grey owl (Strix nebulosaFörster; Aves: Strigidae) (n= 142), barred owl (Strix variaBarton; Aves: Strigidae) (n= 10), northern hawk owl (Surnia ulula(Linnaeus); Aves: Strigidae) (n= 18), short-eared owl (Asio flammeus(Pontoppidan); Aves: Strigidae) (n= 74), long-eared owl (Asio otus(Linnaeus); Aves: Strigidae) (n= 67), eastern screech owl (Megascops aslo(Linnaeus); Aves: Strigidae) (n= 59), boreal owl (Aegolius funereus(Linnaeus); Aves: Strigidae) (n= 47), and northern saw-whet owl (Aegolius acadicus(Gmelin); Aves: Strigidae) (n= 44), a total of 802 owls. No lice were found infesting barn owl (Tyto alba(Scopoli); Aves: Tytonidae) or eastern screech owl (Megascops asio(Linnaeus); Aves: Strigidae). We collected a total of 113 810 lice of 12 species:KurodaiaUchida (Phthiraptera: Menoponidae) – three species; andStrigiphilusMjöberg (Phthiraptera: Philopteridae) – nine species. Overall prevalence of infestation ranged from 10.0% to 88.9%. Mean intensity for total lice ranged from 22.4 to 506.5. Infestation parameters for each louse–host combination are provided; prevalence and mean intensity were not related for louse–host species combinations. Distribution of louse infestations was highly aggregated. In all louse–host combinations but one, either females were more prevalent than males or there was no significant deviation from 50:50. MaleStrigiphilus ceblebrachysDenny significantly outnumbered females in snowy owls. There was a tendency for louse species to co-occur on the same host specimen. Where sample sizes for owls were large enough, no seasonal patterns in abundance of lice were detected.

Diet composition of the Long-eared Owl (Asio otus) in the Eastern Anatolia (Turkey)

Bu calismada kulakli orman baykusunun (Asio otus) pelet icerikleri analiz edilmistir. Bu calismanin temel amaci, kulakli orman baykusunun yaz mevsiminde bir dag bozkirindaki diyet kompozisyonunu arastirmaktir. Kulakli orman baykusuna ait 130 pelet icerigi calismada kullanilmistir. Pelet iceriginden 9 farkli taksona ait 147 av (pelet basina 1.13 av) oldugu belirlendi. Kucuk memeliler turun diyetinin en onemli kismini olusturmaktadir. Yalnizca iki tane kus kalintisina peletlerde rastlanmistir. Microtus sp., turun diyetinde onemli bir av olarak tespit edildi (F =% 81.63, B =% 78.21). Microtus sp. kulakli orman baykusunun favori avi oldugu icin bu durum diyet icerigindeki av cesitliligi ile negatif korelasyona sebep olmaktadir. Bu nedenle FNB ve Shannon-Wiener indeksi dusuk degerdedir.

IMAGES OF AN EARED BIRD OR WHOSE EARS A GRIFFIN HAS?

The article is devoted to the definition of the pre-image for the images of fantastic creatures, which are called in research, eared griffins. The reason for this was the finding in the horse grave number 1 of the barrow number 6 at the town of Dnieprorudny the figurine of a predatory ornithomorphic with ears decorated a bronze molded noseband. Such nosebands are present both in the steppe and in the forest-steppe Scythian monuments of the 4th century BC.
 Researchers have determined that in searching for the origins of the image of the griffin, natural prototypes should be taken into account, finding similarities with the eagles and the vultures of the Old World. It is assumed that the presence of an ear in ornithomorphic images, which is absent in birds, reflects the result of comprehension of reality, and not its fixation. However, in nature there are birds, in the plumage of which there are long feather «ears». These birds are owls, among which eagle-owl and long-eared owls deserve special attention. The attitude of a human being to owls has always been special because of the mysterious nightlife, silent flight and eerie voice. Therefore, it is possible that the ear in the iconography of an ornithomorphic griffin as a result of fixing a real creature and further understanding its image in time and space.

Nocturnal noise and habitat homogeneity limit species richness of owls in an urban environment

Habitat loss and fragmentation are listed among the most significant effects of urbanization, which is regarded as an important threat to wildlife. Owls are the top predators in most terrestrial habitats, and their presence is a reliable indicator of ecosystem quality and complexity. However, influence of urbanization on owl communities, anthropogenic noise in particular, has not been investigated so far. The aim of this study was to identify the role of noise and landcover heterogeneity in the species richness of owl assemblage in the urban ecosystem. Owls were surveyed in the city of Kraków (southern Poland) on 65 randomly selected sample plots (1 km2). The area of main landcover types, landcover diversity index, mean size of landcover patch, and nocturnal noise level were defined within the sample plots and correlated with owl species richness. Five owl species were recorded in the study area with forests as the dominant landcover type for Tawny and Ural owls, grasslands for Long-eared and Barn owls, and gardens for Little owls. In total, 52% of sample plots were occupied by at least one species (1–3 species per plot). The number of owl species was positively correlated with landcover diversity index and negatively correlated with nocturnal noise emission. This study demonstrates that species richness of owls in urban areas may be shaped by landcover heterogeneity and limited by noise intensity. This indicates that noise changes top predator assemblage, which in consequence may disturb predator-prey interactions within human-transformed habitats.

Draft Genome Sequence of Multidrug-Resistant Enterococcus faecium Strain E1298, with a Sequence Type 1274 Profile, Recovered from the Cloacal Microbiome of a Tropical Screech Owl (Megascops choliba) in Rio de Janeiro, Brazil.

Here, we present the draft genome sequence of Enterococcus faecium strain E1298, a representative of the clonal complex 17 (CC17), identified as sequence type 1274 (ST1274) and resistant to multiple classes of antimicrobials, isolated from the cloaca of a tropical screech owl (Megascops choliba) in Rio de Janeiro, Brazil.

Owls lack UV-sensitive cone opsin and red oil droplets, but see UV light at night: Retinal transcriptomes and ocular media transmittance

Most diurnal birds have cone-dominated retinae and tetrachromatic colour vision based on ultra-violet/violet-sensitive UV/V cones expressing short wavelength-sensitive opsin 1 (SWS1), S cones expressing short wavelength-sensitive opsin 2 (SWS2), M cones expressing medium wavelength-sensitive opsin (RH2) and L cones expressing long wavelength-sensitive opsin (LWS). Double cones (D) express LWS but do not contribute to colour vision. Each cone is equipped with an oil droplet, transparent in UV/V cones, but pigmented by carotenoids: galloxanthin in S, zeaxanthin in M, astaxanthin in L and a mixture in D cones. Owls (Strigiformes) are crepuscular or nocturnal birds with rod-dominated retinae and optical adaptations for high sensitivity. For eight species, the absence of functional SWS1 opsin has recently been documented, functional RH2 opsin was absent in three of these. Here we confirm the absence of SWS1 transcripts for the Long-eared owl (Asio otus) and demonstrate its absence for the Short-eared owl (Asio flammeus), Tawny owl (Strix aluco) and Boreal owl (Aegolius funereus). All four species had transcripts of RH2, albeit with low expression. All four species express all enzymes needed to produce galloxanthin, but lack CYP2J19 expression required to produce astaxanthin from dietary precursors. We also present ocular media transmittance of the Eurasian eagle owl (Bubo bubo) and Short-eared owl and predict spectral sensitivities of all photoreceptors of the Tawny owl. We conclude that owls, despite lacking UV/V cones, can detect UV light. This increases the sensitivity of their rod vision allowing them, for instance, to see UV-reflecting feathers as brighter signals at night.

Feeding Ecology and Prey Selection by Wintering Long-Eared Owls Asio otus in Mediterranean Agrosystems

The diet composition and dietary patterns of the Long-eared Owl Asiootus were studied in Mediterranean agrosystems in central Crete (Greece) over the winters of 2009–2015. Overall, 2,819 prey items were recovered from 1,207 pellets, belonging to six taxa of mammals, 22 taxa of birds and four taxa of insects. Small mammals were the most common prey species, accounting for 75.8% by frequency and 79.7% by biomass, followed by birds (23.2% and 20.1%); the latter being rather an island component compared to continental regions. The House Mouse Mus musculus was the most important prey species in the owl's diet (56.3%) ahead of the Wood Mouse apodemus sylvaticus (9.51%) and the Black Rat Rattus rattus (7.9%). The species proved to be a significant rodent predator in olive groves and vineyards during winter months, selecting Wood Mouse and young Black Rat more than expected. Long-eared Owl feeding ecology studies could lead to improved land management and agricultural practices in the rural landscapes of the Mediterranean.

On the diet of owls (Strigiformes) in Jordan

Abstract Between 2005 and 2015 I undertook eight trips to Jordan during which I collected pellets from seven owl species. In them 14,203 food items were identified. Mammals (Mammalia, 46 species, 37.9% of prey items) formed the most numerous component, invertebrates (Evertebrata) made up 33.4%, birds (Aves, 25.4%) were represented with at least 104 species, reptiles (Reptilia) came to 3.2%, and two species of amphibian were identified (Amphibia, 0.2%). Pharoah eagle owls (Bubo ascalaphus) and Byzantine eagle owls (Bubo bubo interpositus) primarily hunt larger mammals and birds, although Agamidae and Scorpiones were also represented more frequently among B. ascalaphus. Mammals predominated among tawny owls (Strix aluco wilkonskii) (Mammalia, 58.9%), mainly the eastern rock mouse (Apodemus mystacinus) (24.9%). For wintering long-eared owls Asio otus otus the most important food was small birds (Aves, 78.3%), especially house sparrows (Passer domesticus), Fringillidae and Sylviidae. For barn owls (Tyto alba erlangeri) the principal prey was small mammals (83.1%), mainly mice (Mus sp.), Günther’s vole (Microtus guentheri), grey hamster (Cricetulus migratorius) and shrews (Soricidae). Hume’s tawny owl (Strix butleri) pellets contained mostly invertebrates (58.9%) and lizards, and their most frequent mammal prey were Wagner’s gerbil (Gerbillus dasyurus) and spiny mice (Acomys sp.). There was an even higher propostion of invertebrates (86.4%) among lilith owlets (Athene lilith). In addition to the insect orders Coleoptera, Orthoptera and Hymenoptera, remains of Scorpiones and Solifugae were also frequently found. The summarized results from individual owl species are compared with those gathered by the author in the surrounding Middle Eastern countries: Israel, Syria, Lebanon and Egypt.

Numerical investigation of aerodynamic and acoustic characteristics of bionic airfoils inspired by bird wing

Airfoil is the basic element of fluid machinery and aircraft, and the noise generated from that is an important research aspect. Aiming to reduce the aerodynamic noise around the airfoil, this study proposes an airfoil inspired by the long-eared owl wing and another airfoil coupled with the bionic airfoil profile, leading edge waves, and trailing edge serrations. Numerical simulations dependent on the large eddy simulation method coupled with the wall-adapting local eddy-viscosity model and the Ffowcs Williams and Hawkings equation are conducted to compare the aerodynamic and acoustic characteristics of two types of bionic airfoils at low Reynolds number condition. The simulations reveal the dipole characteristic of acoustic source and sound pressure level distribution at various frequencies. Two types of bionic airfoils show lower noise compared with the conventional NACA 0012 airfoil with a similar relative thickness of 12%. Compared with the bionic airfoil, the average value of sound pressure level at the monitoring points around the bionic coupling airfoil is decreased by 9.94 dB, meanwhile the lift-to-drag ratio also keep higher. The bionic coupling airfoil exerts a suppression of sound pressure fluctuation on the airfoil surfaces, which result from that the range and size of separation vortices are reduced and the distance between vortices and airfoil surface are increased. The tube-shaped vortices in the wake of airfoil are effectively restrained and split into small scale vortices, which are important to cause less aerodynamic noise around the bionic coupling airfoil. Consequently, a novel bionic coupling airfoil is developed with the excellent aerodynamic and acoustic performance.

Detection and Phylogenetic Analysis of Herpesviruses Detected in Wild Owls in Slovenia.

Herpesvirus (HV) was detected using PCR in the organs of eight of 55 wild owls (14.5%) from seven species that were found dead in various locations in Slovenia between 1995 and 2015. HV was detected in three species: the Eurasian eagle owl (Bubo bubo), Ural owl (Strix uralensis), and long-eared owl (Asio otus). Phylogenetic analysis of partial DNA polymerase gene nucleotide sequences showed that the detected HVs are similar to the avian and mammal alphaherpesviruses. Two sequences were very similar to known bird HV sequences. One sequence was identical to the columbid herpesvirus 1 (CoHV1) sequence, and the other was very similar to the gallid herpesvirus 2 (GaHV2) sequence. The phylogenetic tree revealed a lower similarity of the other six analyzed Slovenian sequences with the sequences of alphaherpesviruses of birds and mammals. This is the first study to report the detection of different HVs in owls.

The relationship between intra–guild diet overlap and breeding in owls in Israel

AbstractEven though intra‐guild predators frequently prey on the same species, it is unclear whether diet overlap between two predators is a source of interspecific competition or whether predators simply use the same abundant prey resource. We measured the extent to which the diets of barn owls (Tyto alba) and long‐eared owls (Asio otus) in Israel overlap and examined whether yearly differences in diet overlap correlate with barn owl breeding success. Pianka's index of niche overlap was positively related to barn owl population size but not to its breeding success. The number of breeding barn owls was higher when long‐eared owls consumed more rodents, suggesting that diet overlap most likely increased when rodents became more abundant. Therefore, in Israel, when these two owl species prey more often on rodents, their diets are more similar and interspecific competition is reduced. Unlike sympatric populations in Europe, in years when rodents are less abundant in Israel long‐eared owls switch to hunting alternative prey (e.g., birds), perhaps to avoid competition with barn owls.

Winter Roost Tree Selection and Phenology of the Long-Eared Owl (Asio otus) in Crimea

The winter roost of the long-eared owl Asio otus in Crimea (South of Ukraine), located in Simferopol, is described. In 2015–2017, the number of long-eared owls varied on a convex curve, with the maximum reached at the end of November and in December. The birds exhibited a strong preference for roosting in conifers, where we recorded 89% of the owls. There was an inverse relationship between the mean of the maximum daily temperature (°C) and the number of owls in both seasons. The owls were not sensitive to abrupt but short-term temperature changes, but the temperature decrease curve caused practically synchronous changes in the dynamics of bird numbers. It was found that the number of owls significantly differed based on weather conditions in 16 trees. The proportion of owls sitting on coniferous trees increased with unfavourable weather, and the converse pattern was observed for deciduous trees.

Investigating spatial patterns of mercury and rodenticide residues in raptors collected near the Charlotte, NC, USA, metropolitan area.

Raptor population growth is dynamic and trends vary across species and by location in the United States. For those species that are declining, it is important to identify potential causes including chemical contaminants. Sampling wild raptors is problematic due to their small population sizes and role as a top predator. Therefore, we obtained liver samples (n = 56) from carcasses of several raptor species, including common species like red-tailed hawks, red-shouldered hawks, barred owls, great horned owls, and osprey that arrived dead or were euthanized from a non-profit rehabilitation center in Charlotte, North Carolina. Raptors were found or collected in South Carolina, North Carolina, and Virginia, but most samples were located near the metropolitan region of Charlotte, NC. We analyzed livers for total mercury residue (mg/kg, dry weight) and five anti-coagulant rodenticides (μg/kg wet weight). Mercury was analyzed using a direct mercury analyzer approach and rodenticides were quantified by LC-MS. Mercury residues were high in piscivorous birds (15.09mg/kg for osprey and 6.93mg/kg for great blue herons, dry weight) and relatively high in red-shouldered hawks and one eastern screech owl tested. Six of our samples exceeded a health threshold of 1mg/kg (wet weight) including three osprey and one each of great blue heron, red-shouldered hawk, and eastern screech owl. Brodifacoum was the only rodenticide consistently detected in our samples. Brodifacoum detections exceeded 75% in barred owls, great horned owls, and red-shouldered hawks. Sixty-nine percent of owl samples were within (or exceeded) a threshold of brodifacoum residue associated with a 10-20% risk of acute toxicity. Correlations between residues and human population density were not significant for either mercury or brodifacoum. Our data suggest that mercury residues for most raptors were not of significant concern with the exception of osprey and possibly red-shouldered hawks. Rodenticide exposures associated with a risk of acute toxicity appear to be common and warrant further investigation.

Home Range and Habitat Selection of Long-Eared Owls (Asio Otus) in Mediterranean Agricultural Landscapes (Crete, Greece)

The Long-eared Owl (Asio otus) in Crete (Greece) is a common agricultural species affected by the recent changes in agro-forestry systems. Concrete studies of habitat selection are needed in order to improve our knowledge of its foraging behaviour in managed rural landscapes. In the present study, we analysed the home range size and habitat selection of 11 Long-eared Owls inside olive groves in the plain of central Crete using radio tracking data and remote sensing images. Six nominal scale and 11 landscape scale predictors were used for habitat selection analysis, using a maximum entropy approach. Home range size ranged between 337 and 969 ha while a 52% of home range overlap was observed suggesting that Long-eared Owls do not defend hunting territories. At the nominal scale, distance to potential roosts (trees) was the most important contributor to model performance, followed by vegetation heterogeneity. Furthermore, local heterogeneity of greenness was a better predictor than simply greenness at the presence location. At the landscape scale the amount of habitat openness significantly improved model performance. Incorporating landscape heterogeneity improved habitat selection prediction compared to using only discrete land cover classification. Results of our study pinpoint that although Long-eared Owls exhibit a wide range of habitat tolerance, they prefer mixed habitat conditions avoiding particularly open areas or dense olive plantations. The research has implications in the face of new reforms of European Common Agricultural policy which emphasised the importance of landscape structure in preserving biodiversity in agricultural areas of Europe.

Responses of Blue Jays (Cyanocitta Cristata) to Raptors that Differ in Predatory Threat

Some species of birds use their vocalisations to communicate predator presence and the level of threat they pose, including two species of corvids (Corvidae), American Crows (Corvus brachyrhynchos) and Siberian Jays (Perisoreus infaustus). Our objective was to determine if Blue Jays (Cyanocitta cristata), another corvid, also use specific calls or vary the characteristics of certain calls to convey information about the level of threat posed by aerial predators. During the non-breeding seasons of 2014 and 2015, we recorded and analysed the vocal responses of Blue Jays to study skins of six species of raptors that varied in size and the level of threat they pose to Blue Jays. Experiments were conducted at seven locations in Madison County, Kentucky. The mean number of Blue Jays present during trials was 2.6, and Blue Jays uttered five different vocalisations during trials, with ditonal and monotonal jeers given most frequently. The rate at which Blue Jays uttered ditonal jeers differed among trials, with rates highest during trials with an Eastern Screech-Owl (Megascops asio) and a Sharp-shinned Hawk (Accipiter striatus). However, the characteristics of ditonal and monotonal jeers (duration, low frequency, high frequency, and peak frequency) did not differ among trials. These results suggest that Blue Jays may either perceive Eastern Screech-Owls and Sharp-shinned Hawks as the greatest threats or, alternatively, as potential, but less threatening predators, and, therefore, they were willing to take greater risks when mobbing them. In contrast, Blue Jays mobbed the other raptors, i.e. American Kestrels (Falco sparverius), Red-tailed Hawks (Buteo jamaicensis), and Great Horned Owls (Bubo virginianus), with much less intensity, likely because they posed less of a threat or, in the case of Cooper's Hawks (Accipiter cooperii) that are known predators of Blue Jays, perhaps because mobbing with greater intensity, e.g. approaching more closely, posed too great a risk. Blue Jays in our study used the same calls with the same characteristics when responding to potential predators, only calling rates differed. However, such variation in calling rates when mobbing would likely provide useful information about the presence of, and possibly the threat posed by, potential predators for conspecifics and, perhaps, heterospecifics.