The barn owls' Minimum Audible Angle

Interaural time differences (ITD) and interaural level differences (ILD) are physical cues that enable the auditory system to pinpoint the position of a sound source in space. This ability is crucial for animal communication and predator-prey interactions. The barn owl has evolved an exceptional sense of hearing and shows abilities of sound localisation that outperform most other species. So far, behavioural studies in the barn owl often used reflexive responses to investigate aspects of sound localisation. Furthermore, they predominately probed the higher frequencies of the owl's hearing range (> 3 kHz). In the present study we used a Go/NoGo paradigm to measure the barn owl's behavioural sound localisation acuity (expressed as the Minimum Audible Angle, MAA) as a function of stimulus type (narrow-band noise centred at 500, 1000, 2000, 4000 and 8000 Hz, and broad-band noise) and sound source position. We found significant effects of both stimulus type and sound source position on the barn owls' MAA. The MAA improved with increasing stimulus frequency, from 14° at 500 Hz to 6° at 8000 Hz. The smallest MAA of 4° was found for broadband noise stimuli. Comparing different sound source positions revealed smaller MAAs for frontal compared to lateral stimulus presentation, irrespective of stimulus type. These results are consistent with both the known variations in physical ITDs and variation in the width of neural ITD tuning curves with azimuth and frequency. Physical and neural characteristics combine to result in better spatial acuity for frontal compared to lateral sounds and reduced localisation acuity at lower frequencies.

Dental Microwear and Mesowear of the Microtus Voles Molars before and after Experimental Feeding of Owls

In small mammals, the degree of micro- and mesowear of molars depends on the feed hardness, abrasiveness, and some other characteristics. Analysis of micro- and mesorelief of the paleontological material is used for reconstruction of some animal diet parameters. Small mammals pass through a series of complex transformations on the way from the objects of biocenosis to paleontological objects. Bone remains underwent transformations during accumulation and fossilization. In particular, bone remains from ornithogenous deposits were exposed to the bird digestive system elements. We have experimentally studied changes in some parameters of the narrow-headed vole (Microtus gregalis) molars derived from the owl pellets. Comparison of the same samples before and after exposure to the digestive system of the polar owl (Nyctea scandiaca) and eagle owl (Bubo bubo) showed that the tooth enamel microrelief undergoes serious changes and therefore, provides no information on the intravital diet of voles. A different degree of preservation of the characteristics of the mesorelief was shown. Depending on this, an assessment of their applicability to paleoreconstructions was given.

Effects of presentation rate and onset time on auditory brainstem responses in Northern saw-whet owls (Aegolius acadicus)

Monitoring auditory brainstem responses (ABRs) is a common method of assessing auditory processing in non-model species. Although ABRs are widely used to compare auditory abilities across taxa, the extent to which different features of acoustic stimuli affect the ABR is largely unknown in most non-mammalian species. The authors investigated the effects of varying presentation rate and onset time to determine how different features of acoustic stimuli influence the ABR in Northern saw-whet owls (Aegolius acadicus), a species known for their unique auditory adaptations and hunting abilities. At presentation rates ranging from 21.1 to 51.1 s^-1, there were no differences in the size or synchrony of ABRs, suggesting that stimuli can be presented at a relatively rapid rate to maximize the number of observations recorded for analysis. While increasing onset time was associated with a decrement in response size and synchrony, tonebursts with 1 ms onset times produced overgeneralized neural responses as a result of spectral splatter. This suggests that 2 to 3 ms onset times may balance the trade-off between response synchrony and frequency specificity when comparing relative neural recruitment across frequencies. These findings highlight the importance of considering stimulus parameters when interpreting ABR data.

Describing vegetation characteristics used by two rare forest-dwelling species: Will established reserves provide for coastal marten in Oregon?

Forest management guidelines for rare or declining species in the Pacific Northwest, USA, include both late successional reserves and specific vegetation management criteria. However, whether current management practices for well-studied species such as northern spotted owls (Strix occidentallis caurina) can aid in conserving a lesser known subspecies-Humboldt martens (Martes caurina humboldtensis)-is unclear. To address the lack of information for martens in coastal Oregon, USA, we quantified vegetation characteristics at locations used by Humboldt martens and spotted owls in two regions (central and southern coast) and at two spatial scales (the site level summarizing extensive vegetation surveys and regionally using remotely sensed vegetation and estimated habitat models). We estimated amount of predicted habitat for both species in established reserves. If predicted overlap in established reserves was low, then we reported vegetation characteristics to inform potential locations for reserves or management opportunities. In the Central Coast, very little overlap existed in vegetation characteristics between Humboldt martens and spotted owls at either the site or regional level. Humboldt martens occurred in young forests composed of small diameter trees with few snags or downed logs. Humboldt martens were also found in areas with very dense vegetation when overstory canopy and shrub cover percentages were combined. In the South Coast, Humboldt martens occurred in forests with smaller diameter trees than spotted owl sites on average. Coastal Humboldt martens may use stands of predicted high quality spotted owl habitat in the Pacific Northwest. Nonetheless, our observations suggest that coastal Humboldt martens exist in areas that include a much higher diversity of conifer size classes as long as extensive dense shrub cover, predominantly in the form of high salal and evergreen huckleberry, are available. We suggest that managers consider how structural characteristics (e.g., downed logs, shrub cover, patch size), are associated with long-term species persistence rather than relying on reserves based on broad cover types. Describing vegetation may partially describe suitability, but available prey or predation risk ultimately influence likelihood of individual Humboldt marten use. Guidelines for diversifying vegetation management, and retaining or restoring appropriate habitat conditions at both the stand level and regionally, may increase management flexibility and identify forest conditions that support both spotted owls and Humboldt martens.

Numerical investigation of low-noise airfoils inspired by the down coat of owls

Numerical analysis of airfoil geometries inspired by the down coat of the night owl is presented. The bioinspired geometry consists of an array of 'finlet fences', which is placed near the trailing edge of the baseline (NACA 0012) airfoil. Two fences with maximum nondimensional heights, [Formula: see text] and [Formula: see text] are investigated, where [Formula: see text] is the displacement thickness at 2.9% chord upstream of the airfoil trailing edge. Wall-resolved large eddy simulations are performed at chord-based Reynolds number, [Formula: see text], flow Mach number, [Formula: see text], and angle of attack, [Formula: see text]. The simulation results show significant reductions in unsteady surface pressure and farfield radiated noise with the fences, in agreement with the measurements available in the literature. Analysis of the results reveals that the fences increase the distance between the boundary layer turbulence (source) and the airfoil trailing (scattering) edge, which is identified to be the mechanism behind high-frequency noise reduction. These reductions are larger for the taller fence as the source-scattering edge separation is greater. Two-point correlations show that the fences reduce the spanwise coherence at low frequencies for separation distances greater than a fence pitch (distance between two adjacent fences) and increase the coherence for smaller distances, the increase being higher for the taller fence. This increase in coherence and the reduced obliqueness of the leading edge of the fence are hypothesized to be responsible for the small increase in farfield noise at low frequencies observed in the simulations with the taller fence.

Aerodynamic robustness in owl-inspired leading-edge serrations: a computational wind-gust model

Owls are a master to achieve silent flight in gliding and flapping flights under natural turbulent environments owing to their unique wing morphologies. While the leading-edge serrations are recently revealed, as a passive flow control micro-device, to play a crucial role in aerodynamic force production and sound suppression (Rao et al 2017 Bioinspiration Biomim. 12 1-13), the characteristics of wind-gust rejection associated with leading-edge serrations remain unclear. Here we address a large-eddy simulation-based study of aerodynamic robustness in owl-inspired leading-edge serrations, which is conducted with clean and serrated wing models through mimicking wind-gusts under a longitudinal fluctuation in free-stream inflow and a lateral fluctuation in pitch angle over a broad range of angles of attack (AoAs) over 0°  ⩽  Φ  ⩽  20°. Our results show that the leading-edge serration-based passive flow control mechanisms associated with laminar-turbulent transition work effectively under fluctuated inflow and wing pitch, indicating that the leading-edge serrations are of potential gust fluctuation rejection or robustness in aerodynamic performance. Moreover, it is revealed that the tradeoff between turbulent flow control (i.e. aero-acoustic suppression) and force production in the serrated model holds independently to the wind-gust environments: poor at lower AoAs but capable of achieving equivalent aerodynamic performance at higher AoAs  >15° compared to the clean model. Our results reveal that the owl-inspired leading-edge serrations can be a robust micro-device for aero-acoustic control coping with unsteady and complex wind environments in biomimetic rotor designs for various fluid machineries.

Metal Concentrations in Eurasian Eagle Owl Pellets as a Function of Reproductive Variables in Korea

Eight metals were analyzed in the pellet of Eurasian eagle owls (Bubo bubo) breeding in Korea: Paju, Ganghwa, Gimpo, and Sihwa, Gyeonggi-do (N = 15, respectively). Except for cadmium (Cd), concentrations of all metals differed among sites (ANOVA, p < 0.001); Sihwa had relatively higher metal concentrations compared with other sites. Clutch size did not differ among the four sites. However, Sihwa had the greatest nesting success and number of fledglings (per hatchlings and laid egg) and highest mean weight of diet. Lead concentrations in the pellets were generally lower than the excrements of various birds worldwide. We suggest that all metal concentrations in pellets do not negatively affect the reproduction of Eurasian eagle owls, and food supply at Sihwa seems likely more important to breeding success than metal contamination.

From biokinematics to a robotic active vision system

Barn owls move their heads in very particular motions, compensating for the quasi-immovability of their eyes. These efficient predators often perform peering side-to-side head motions when scanning their surroundings and seeking prey. In this work, we use the head movements of barn owls as a model to bridge between biological active vision and machine vision. The biomotions are measured and used to actuate a specially built robot equipped with a depth camera for scanning. We hypothesize that the biomotions improve scan accuracy of static objects. Our experiments show that barn owl biomotion-based trajectories consistently improve scan accuracy when compared to intuitive scanning motions. This constitutes proof-of-concept evidence that the vision of robotic systems can be enhanced by bio-inspired viewpoint manipulation. Such biomimetic scanning systems can have many applications, e.g. manufacturing inspection or in autonomous robots.

Determination of Gastrointestinal Transit Times in Barred Owls ( Strix varia ) by Contrast Fluoroscopy

Contrast imaging studies are routinely performed in avian patients when an underlying abnormality of the gastrointestinal (GI) tract is suspected. Fluoroscopy offers several advantages over traditional radiography and can be performed in conscious animals with minimal stress and restraint. Although birds of prey are commonly encountered as patients, little is known about GI transit times and contrast imaging studies in these species, especially owls. Owls are commonly encountered in zoological, educational, and wildlife settings. In this study, 12 adult barred owls ( Strix varia ) were gavage fed a 30% weight-by-volume barium suspension (25 mL/kg body weight). Fluoroscopic exposures were recorded at 5, 15, 30, 60, 120, 180, 240, and 300 minutes after administration. Overall GI transit time and transit times of various GI organs were recorded. Median (interquartile range [IQR]) overall GI transit time was 60 minutes (IQR: 19-60 minutes) and ranged from 5-120 minutes. Ventricular and small intestinal contrast filling was rapid. Ventricular emptying was complete by a median of 60 minutes (IQR: 30-120 minutes; range: 30-240 minutes), whereas small intestinal emptying was not complete in 9/12 birds by 300 minutes. Median small intestinal contraction rate was 15 per minute (IQR: 13-16 minutes; range: 10-19 minutes). Median overall GI transit time in barred owls is more rapid than mean transit times reported for psittacine birds and red-tailed hawks ( Buteo jamaicensis ). Fluoroscopy is a safe, suitable method for investigating GI motility and transit in this species.

Owl-inspired leading-edge serrations play a crucial role in aerodynamic force production and sound suppression

Owls are widely known for silent flight, achieving remarkably low noise gliding and flapping flights owing to their unique wing morphologies, which are normally characterized by leading-edge serrations, trailing-edge fringes and velvet-like surfaces. How these morphological features affect aerodynamic force production and sound suppression or noise reduction, however, is still not well known. Here we address an integrated study of owl-inspired single feather wing models with and without leading-edge serrations by combining large-eddy simulations (LES) with particle-image velocimetry (PIV) and force measurements in a low-speed wind tunnel. With velocity and pressure spectra analysis, we demonstrate that leading-edge serrations can passively control the laminar-turbulent transition over the upper wing surface, i.e. the suction surface at all angles of attack (0°  <  AoA  <  20°), and hence play a crucial role in aerodynamic force and sound production. We find that there exists a tradeoff between force production and sound suppression: serrated leading-edges reduce aerodynamic performance at lower AoAs  <  15° compared to clean leading-edges but are capable of achieving both noise reduction and aerodynamic performance at higher AoAs  >  15° where owl wings often reach in flight. Our results indicate that the owl-inspired leading-edge serrations may be a useful device for aero-acoustic control in biomimetic rotor designs for wind turbines, aircrafts, multi-rotor drones as well as other fluid machinery.

Home range size of Tengmalm's owl during breeding in Central Europe is determined by prey abundance

Animal home ranges typically characterized by their size, shape and a given time interval can be affected by many different biotic and abiotic factors. However, despite the fact that many studies have addressed home ranges, our knowledge of the factors influencing the size of area occupied by different animals is, in many cases, still quite poor, especially among raptors. Using radio-telemetry (VHF; 2.1 g tail-mounted tags) we studied movements of 20 Tengmalm’s owl (Aegolius funereus) males during the breeding season in a mountain area of Central Europe (the Czech Republic, the Ore Mountains: 50° 40’ N, 13° 35’ E) between years 2006–2010, determined their average hunting home range size and explored what factors affected the size of home range utilised. The mean breeding home range size calculated according to 95% fixed kernel density estimator was 190.7 ± 65.7 ha (± SD) with a median value of 187.1 ha. Home range size was affected by prey abundance, presence or absence of polygyny, the number of fledglings, and weather conditions. Home range size increased with decreasing prey abundance. Polygynously mated males had overall larger home range than those mated monogamously, and individuals with more fledged young possessed larger home range compared to those with fewer raised fledglings. Finally, we found that home ranges recorded during harsh weather (nights with strong wind speed and/or heavy rain) were smaller in size than those registered during better weather. Overall, the results provide novel insights into what factors may influence home range size and emphasize the prey abundance as a key factor for breeding dynamics in Tengmalm’s owl.

Low frequency eardrum directionality in the barn owl induced by sound transmission through the interaural canal

The middle ears of birds are typically connected by interaural cavities that form a cranial canal. Eardrums coupled in this manner may function as pressure difference receivers rather than pressure receivers. Hereby, the eardrum vibrations become inherently directional. The barn owl also has a large interaural canal, but its role in barn owl hearing and specifically in sound localization has been controversial so far. We discuss here existing data and the role of the interaural canal in this species and add a new dataset obtained by laser Doppler vibrometry in a free-field setting. Significant sound transmission across the interaural canal occurred at low frequencies. The sound transmission induces considerable eardrum directionality in a narrow band from 1.5 to 3.5 kHz. This is below the frequency range used by the barn owl for locating prey, but may conceivably be used for locating conspecific callers.

Increased rodenticide exposure rate and risk of toxicosis in barn owls (Tyto alba) from southwestern Canada and linkage with demographic but not genetic factors

Among many anthropogenic drivers of population decline, continual rapid urbanization and industrialization pose major challenges for the survival of wildlife species. Barn owls (Tyto alba) in southwestern British Columbia (BC) face a multitude of threats ranging from habitat fragmentation to vehicle strikes. They are also at risk from secondary poisoning of second-generation anticoagulant rodenticides (SGARs), a suite of toxic compounds which at high doses results in a depletion of blood clotting factors leading to internal bleeding and death. Here, using long-term data (N = 119) for the hepatic residue levels of SGAR, we assessed the risk of toxicosis from SGAR for the BC barn owl population over the past two decades. We also investigated whether sensitivity to SGAR is associated with genetic factors, namely Single Nucleotide Polymorphisms (SNPs) found in the CYP2C45 gene of barn owls. We found that residue concentration for total SGAR was significantly higher in 2006-2013 (141 ng/g) relative to 1992-2003 (57 ng/g). The proportion of owls exposed to multiple SGAR types was also significantly higher in 2006-2013. Those measures accordingly translate directly into an increase in toxicosis risk level. We also detected demographic differences, where adult females showed on average lower concentration of total SGAR (64 ng/g) when compared to adult males (106 ng/g). Juveniles were overall more likely to show signs of toxicosis than adults (33.3 and 6.9 %, respectively), and those symptoms were positively predicted by SGAR concentrations. We found no evidence that SNPs in the CYP2C45 gene of barn owls were associated with intraspecific variation in SGAR sensitivity. We recommend several preventative measures be taken to minimize wildlife exposure to SGAR.

Multistate Models Reveal Long-Term Trends of Northern Spotted Owls in the Absence of a Novel Competitor

Quantifying spatial and temporal variability in population trends is a critical aspect of successful management of imperiled species. We evaluated territory occupancy dynamics of northern spotted owls (Strix occidentalis caurina), California, USA, 1990–2014. The study area possessed two unique aspects. First, timber management has occurred for over 100 years, resulting in dramatically different forest successional and structural conditions compared to other areas. Second, the barred owl (Strix varia), an exotic congener known to exert significant negative effects on spotted owls, has not colonized the study area. We used a Bayesian dynamic multistate model to evaluate if territory occupancy of reproductive spotted owls has declined as in other study areas. The state-space approach for dynamic multistate modeling imputes the number of territories for each nesting state and allows for the estimation of longer-term trends in occupied or reproductive territories from longitudinal studies. The multistate approach accounts for different detection probabilities by nesting state (to account for either inherent differences in detection or for the use of different survey methods for different occupancy states) and reduces bias in state assignment. Estimated linear trends in the number of reproductive territories suggested an average loss of approximately one half territory per year (-0.55, 90% CRI: -0.76, -0.33), in one management block and a loss of 0.15 per year (-0.15, 90% CRI: -0.24, -0.07), in another management block during the 25 year observation period. Estimated trends in the third management block were also negative, but substantial uncertainty existed in the estimate (-0.09, 90% CRI: -0.35, 0.17). Our results indicate that the number of territories occupied by northern spotted owl pairs remained relatively constant over a 25 year period (-0.07, 90% CRI: -0.20, 0.05; -0.01, 90% CRI: -0.19, 0.16; -0.16, 90% CRI: -0.40, 0.06). However, we cannot exclude small-to-moderate declines or increases in paired territory numbers due to uncertainty in our estimates. Collectively, we conclude spotted owl pair populations on this landscape managed for commercial timber production appear to be more stable and do not show sharp year-over-year declines seen in both managed and unmanaged landscapes with substantial barred owl colonization and persistence. Continued monitoring of reproductive territories can determine whether recent declines continue or whether trends reverse as they have on four previous occasions. Experimental investigations to evaluate changes to spotted owl occupancy dynamics when barred owl populations are reduced or removed entirely can confirm the generality of this conclusion.

Combined particle-image velocimetry and force analysis of the three-dimensional fluid-structure interaction of a natural owl wing

Low-speed aerodynamics has gained increasing interest due to its relevance for the design process of small flying air vehicles. These small aircraft operate at similar aerodynamic conditions as, e.g. birds which therefore can serve as role models of how to overcome the well-known problems of low Reynolds number flight. The flight of the barn owl is characterized by a very low flight velocity in conjunction with a low noise emission and a high level of maneuverability at stable flight conditions. To investigate the complex three-dimensional flow field and the corresponding local structural deformation in combination with their influence on the resulting aerodynamic forces, time-resolved stereoscopic particle-image velocimetry and force and moment measurements are performed on a prepared natural barn owl wing. Several spanwise positions are measured via PIV in a range of angles of attack [Formula: see text] 6° and Reynolds numbers 40 000 [Formula: see text] 120 000 based on the chord length. Additionally, the resulting forces and moments are recorded for -10° ≤ α ≤ 15° at the same Reynolds numbers. Depending on the spanwise position, the angle of attack, and the Reynolds number, the flow field on the wing's pressure side is characterized by either a region of flow separation, causing large-scale vortical structures which lead to a time-dependent deflection of the flexible wing structure or wing regions showing no instantaneous deflection but a reduction of the time-averaged mean wing curvature. Based on the force measurements the three-dimensional fluid-structure interaction is assumed to considerably impact the aerodynamic forces acting on the wing leading to a strong mechanical loading of the interface between the wing and body. These time-depending loads which result from the flexibility of the wing should be taken into consideration for the design of future small flying air vehicles using flexible wing structures.

Morphological Variations of Leading-Edge Serrations in Owls (Strigiformes)

Background

Owls have developed serrations, comb-like structures, along the leading edge of their wings. Serrations were investigated from a morphological and a mechanical point of view, but were not yet quantitatively compared for different species. Such a comparative investigation of serrations from species of different sizes and activity patterns may provide new information about the function of the serrations.

Results

Serrations on complete wings and on tenth primary remiges of seven owl species were investigated. Small, middle-sized, and large owl species were investigated as well as species being more active during the day and owls being more active during the night. Serrations occurred at the outer parts of the wings, predominantly at tenth primary remiges, but also on further wing feathers in most species. Serration tips were oriented away from the feather rachis so that they faced into the air stream during flight. The serrations of nocturnal owl species were higher developed as demonstrated by a larger inclination angle (the angle between the base of the barb and the rachis), a larger tip displacement angle (the angle between the tip of the serration and the base of the serration) and a longer length. Putting the measured data into a clustering algorithm yielded dendrograms that suggested a strong influence of activity pattern, but only a weak influence of size on the development of the serrations.

Conclusions

Serrations are supposed to be involved in noise reduction during flight and also depend on the aerodynamic properties that in turn depend on body size. Since especially nocturnal owls have to rely on hearing during prey capture, the more pronounced serrations of nocturnal species lend further support to the notion that serrations have an important function in noise reduction. The differences in shape of the serrations investigated indicate that a silent flight requires well-developed serrations.

Rapid warming and drought negatively impact population size and reproductive dynamics of an avian predator in the arid southwest

Avian communities of arid ecosystems may be particularly vulnerable to global climate change due to the magnitude of projected change for desert regions and the inherent challenges for species residing in resource limited ecosystems. How arid-zone birds will be affected by rapid increases in air temperature and increased drought frequency and severity is poorly understood because avian responses to climate change have primarily been studied in the relatively mesic northern temperate regions. We studied the effects of increasing air temperature and aridity on a Burrowing Owl (Athene cunicularia) population in the southwestern United States from 1998 to 2013. Over 16 years, the breeding population declined 98.1%, from 52 pairs to 1 pair, and nest success and fledgling output also declined significantly. These trends were strongly associated with the combined effects of decreased precipitation and increased air temperature. Arrival on the breeding grounds, pair formation, nest initiation, and hatch dates all showed significant delays ranging from 9.4 to 25.1 days over 9 years, which have negative effects on reproduction. Adult and juvenile body mass decreased significantly over time, with a loss of 7.9% mass in adult males and 10.9% mass in adult females over 16 years, and a loss of 20.0% mass in nestlings over 8 years. Taken together, these population and reproductive trends have serious implications for local population persistence. The southwestern United States has been identified as a climate change hotspot, with projections of warmer temperatures, less winter precipitation, and an increase in frequency and severity of extreme events including drought and heat waves. An increasingly warm and dry climate may contribute to this species' decline and may already be a driving force of their apparent decline in the desert southwest.

Divergence in sink contributions to population persistence

Population sinks present unique conservation challenges. The loss of individuals in sinks can compromise persistence; but conversely, sinks can improve viability by improving connectivity and facilitating the recolonization of vacant sources. To assess the contribution of sinks to regional population persistence of declining populations, we simulated source-sink dynamics for 3 very different endangered species: Black-capped Vireos (Vireo atricapilla) at Fort Hood, Texas, Ord's kangaroo rats (Dipodomys ordii) in Alberta, and Northern Spotted Owls (Strix occidentalis caurina) in the northwestern United States. We used empirical data from these case studies to parameterize spatially explicit individual-based models. We then used the models to quantify population abundance and persistence with and without long-term sinks. The contributions of sink habitats varied widely. Sinks were detrimental, particularly when they functioned as strong sinks with few emigrants in declining populations (e.g., Alberta's Ord's kangaroo rat) and benign in robust populations (e.g., Black-capped Vireos) when Brown-headed Cowbird (Molothrus ater) parasitism was controlled. Sinks, including ecological traps, were also crucial in delaying declines when there were few sources (e.g., in Black-capped Vireo populations with no Cowbird control). Sink contributions were also nuanced. For example, sinks that supported large, variable populations were subject to greater extinction risk (e.g., Northern Spotted Owls). In each of our case studies, new context-dependent sinks emerged, underscoring the dynamic nature of sources and sinks and the need for frequent re-assessment. Our results imply that management actions based on assumptions that sink habitats are generally harmful or helpful risk undermining conservation efforts for declining populations.

A New Framework for Spatio-temporal Climate Change Impact Assessment for Terrestrial Wildlife

We describe a first step framework for climate change species' impact assessments that produces spatially and temporally heterogeneous models of climate impacts. Case study results are provided for great gray owl (Strix nebulosa) in Idaho as an example of framework application. This framework applies species-specific sensitivity weights to spatial and seasonal models of climate exposure to produce spatial and seasonal models of climate impact. We also evaluated three methods of calculating sensitivity by comparing spatial models of combined exposure and sensitivity. We found the methods used to calculated sensitivity showed little difference, except where sensitivity was directional (i.e., more sensitive to an increase in temperature than a decrease). This approach may assist in the development of State Wildlife Action Plans and other wildlife management plans in the face of potential future climate change.

Factors Affecting Growth of Tengmalm's Owl (Aegolius funereus) Nestlings: Prey Abundance, Sex and Hatching Order

In altricial birds, energy supply during growth is a major predictor of the physical condition and survival prospects of fledglings. A number of experimental studies have shown that nestling body mass and wing length can vary with particular extrinsic factors, but between-year observational data on this topic are scarce. Based on a seven-year observational study in a central European Tengmalm's owl population we examine the effect of year, brood size, hatching order, and sex on nestling body mass and wing length, as well as the effect of prey abundance on parameters of growth curve. We found that nestling body mass varied among years, and parameters of growth curve, i.e. growth rate and inflection point in particular, increased with increasing abundance of the owl's main prey (Apodemus mice, Microtus voles), and pooled prey abundance (Apodemus mice, Microtus voles, and Sorex shrews). Furthermore, nestling body mass varied with hatching order and between sexes being larger for females and for the first-hatched brood mates. Brood size had no effect on nestling body mass. Simultaneously, we found no effect of year, brood size, hatching order, or sex on the wing length of nestlings. Our findings suggest that in this temperate owl population, nestling body mass is more sensitive to prey abundance than is wing length. The latter is probably more limited by the physiology of the species.

Subtle Gardeners: Inland Predators Enrich Local Topsoils and Enhance Plant Growth

Inland vertebrate predators could enrich of nutrients the local top soils in the area surrounding their nests and dens by depositing faeces, urine, and prey remains and, thus, alter the dynamics of plant populations. Surprisingly, and in contrast with convincing evidence from coastal habitats, whether and how this phenomenon occurs in inland habitats is largely uncertain even though these habitats represent a major fraction of the earth's surface. We investigated during two consecutive breeding seasons the potential enrichment of the top-soils associated with inland ground-nesting eagle owls Bubo bubo, as well as its possible consequences in the growth of two common annual grasses in southern Spain. Top-soils associated with owl nests differed strongly and significantly from control top-soils in chemical parameters, mainly fertility-related properties. Specifically, levels of available phosphorus, total nitrogen, organic matter, and available potassium were 49.1, 5.6, 3.1, and 2.7 times higher, respectively, in top-soils associated with owl nests as compared to control top-soils. Germination experiments in chambers indicated that nutrient enrichment by nesting owls enhanced seedling growth in both annual grasses (Phalaris canariensis and Avena sativa), with seedling size being 1.4-1.3 times higher in owl nest top-soils than in control top-soils. Our experimental study revealed that pervasive inland, predatory birds can profoundly enrich the topsoil around their nests and, thus, potentially enhance local vegetation growth. Because diverse inland vertebrate predators are widespread in most habitats they have a strong potential to enhance spatial heterogeneity, impinge on plant communities, and exert an overlooked effect on primary productivity worldwide.

Particle-image velocimetry investigation of the fluid-structure interaction mechanisms of a natural owl wing

The increasing interest in the development of small flying air vehicles has given rise to a strong need to thoroughly understand low-speed aerodynamics. The barn owl is a well-known example of a biological system that possesses a high level of adaptation to its habitat and as such can inspire future small-scale air vehicle design. The combination of the owl-specific wing geometry and plumage adaptations with the flexibility of the wing structure yields a highly complex flow field, still enabling the owl to perform stable and at the same time silent low-speed gliding flight. To investigate the effects leading to such a characteristic flight, time-resolved stereoscopic particle-image velocimetry (TR-SPIV) measurements are performed on a prepared natural owl wing in a range of angles of attack 0° ≤ α ≤ 6° and Reynolds numbers 40,000 ≤ Re(c) ≤ 120,000 based on the chord length at a position located at 30% of the halfspan from the owl's body. The flow field does not show any flow separation on the suction side, whereas flow separation is found on the pressure side for all investigated cases. The flow field on the pressure side is characterized by large-scale vortices which interact with the flexible wing structure. The good agreement of the shedding frequency of the pressure side vortices with the frequency of the trailing-edge deflection indicates that the structural deformation is induced by the flow field on the pressure side. Additionally, the reduction of the time-averaged mean wing curvature at high Reynolds numbers indicates a passive lift-control mechanism that provides constant lift in the entire flight envelope of the owl.

Clutch size of a vole-eating bird of prey as an indicator of vole abundance

Voles are often considered as harmful pests in agriculture and silviculture. Then, the knowledge of their abundance may be of considerable economical importance. Commonly used methods in the monitoring of vole abundances are relatively laborious, expensive, and spatially quite restricted. We demonstrate how the mean clutch size of the tawny owl Strix aluco may be cost-effectively used to predict relative densities of voles over large areas. Besides installing a number of suitable nest boxes, this vole monitoring system primarily includes only the inspection of the nest boxes and counting the number of tawny owl eggs found two times during a few weeks period in spring. Our results showed a considerable agreement between the fluctuations in the mean clutch size of tawny owls and the late spring abundance indices of small voles (Myodes, Microtus) in our study areas in southern Finland. The mean clutch size of the tawny owl reflected spring vole abundance over the spatial range examined, suggesting its suitability for general forecasting purposes. From the pest management point of view, an additional merit of the present method is that it may increase numbers of vole-eaters that provide biological control of vole populations.

Optimal Prediction of Moving Sound Source Direction in the Owl

Capturing nature's statistical structure in behavioral responses is at the core of the ability to function adaptively in the environment. Bayesian statistical inference describes how sensory and prior information can be combined optimally to guide behavior. An outstanding open question of how neural coding supports Bayesian inference includes how sensory cues are optimally integrated over time. Here we address what neural response properties allow a neural system to perform Bayesian prediction, i.e., predicting where a source will be in the near future given sensory information and prior assumptions. The work here shows that the population vector decoder will perform Bayesian prediction when the receptive fields of the neurons encode the target dynamics with shifting receptive fields. We test the model using the system that underlies sound localization in barn owls. Neurons in the owl's midbrain show shifting receptive fields for moving sources that are consistent with the predictions of the model. We predict that neural populations can be specialized to represent the statistics of dynamic stimuli to allow for a vector read-out of Bayes-optimal predictions.

Genetic Signatures of Demographic Changes in an Avian Top Predator during the Last Century: Bottlenecks and Expansions of the Eurasian Eagle Owl in the Iberian Peninsula

The study of the demographic history of species can help to understand the negative impact of recent population declines in organisms of conservation concern. Here, we use neutral molecular markers to explore the genetic consequences of the recent population decline and posterior recovery of the Eurasian eagle owl (Bubo bubo) in the Iberian Peninsula. During the last century, the species was the object of extermination programs, suffering direct persecution by hunters until the 70's. Moreover, during the last decades the eagle owl was severely impacted by increased mortality due to electrocution and the decline of its main prey species, the European rabbit (Oryctolagus cuniculus). In recent times, the decrease of direct persecution and the implementation of some conservation schemes have allowed the species' demographic recovery. Yet, it remains unknown to which extent the past population decline and the later expansion have influenced the current species' pattern of genetic diversity. We used eight microsatellite markers to genotype 235 eagle owls from ten Spanish subpopulations and analyse the presence of genetic signatures attributable to the recent population fluctuations experienced by the species. We found moderate levels of differentiation among the studied subpopulations and Bayesian analyses revealed the existence of three genetic clusters that grouped subpopulations from central, south-western and south-eastern Spain. The observed genetic structure could have resulted from recent human-induced population fragmentation, a patchy distribution of prey populations and/or the philopatric behaviour and habitat selection of the species. We detected an old population bottleneck, which occurred approximately 10,000 years ago, and significant signatures of recent demographic expansions. However, we did not find genetic signatures for a recent bottleneck, which may indicate that population declines were not severe enough to leave detectable signals on the species genetic makeup or that such signals have been eroded by the rapid demographic recovery experienced by the species in recent years.