Facial Ruff Research Articles

Development of frequency tuning shaped by spatial cue reliability in the barn owl's auditory midbrain.

Sensory systems preferentially strengthen responses to stimuli based on their reliability at conveying accurate information. While previous reports demonstrate that the brain reweighs cues based on dynamic changes in reliability, how the brain may learn and maintain neural responses to sensory statistics expected to be stable over time is unknown. The barn owl's midbrain features a map of auditory space where neurons compute horizontal sound location from the interaural time difference (ITD). Frequency tuning of midbrain map neurons correlates with the most reliable frequencies for the neurons' preferred ITD (Cazettes et al., 2014). Removal of the facial ruff led to a specific decrease in the reliability of high frequencies from frontal space. To directly test whether permanent changes in ITD reliability drive frequency tuning, midbrain map neurons were recorded from adult owls, with the facial ruff removed during development, and juvenile owls, before facial ruff development. In both groups, frontally tuned neurons were tuned to frequencies lower than in normal adult owls, consistent with the change in ITD reliability. In addition, juvenile owls exhibited more heterogeneous frequency tuning, suggesting normal developmental processes refine tuning to match ITD reliability. These results indicate causality of long-term statistics of spatial cues in the development of midbrain frequency tuning properties, implementing probabilistic coding for sound localization.

Great Gray Owls hunting voles under snow hover to defeat an acoustic mirage.

How do Great Gray Owls (Strix nebulosa) capture voles (Cricetidae) through a layer of snow? As snow is a visual barrier, the owls locate voles by ear alone. To test how snow absorbs and refracts vole sound, we inserted a loudspeaker under the snowpack and analysed sound from the loudspeaker, first buried, then unburied. Snow attenuation coefficients rose with frequency (0.3 dB cm-1 at 500 Hz, 0.6 dB cm-1 at 3 kHz) such that low-frequency sound transmitted best. The Great Gray Owl has the largest facial disc of any owl, suggesting they are adapted to use this low-frequency sound. We used an acoustic camera to spatially localize sound source location, and show that snow also refracts prey sounds (refractive index: 1.16). To an owl not directly above the prey, this refraction creates an 'acoustic mirage': prey acoustic position is offset from its actual location. Their hunting strategy defeats this mirage because they hover directly over prey, which is the listening position with least refraction and least attenuation. Among all birds, the Great Gray Owl has the most extreme wing morphologies associated with quiet flight. These extreme wing traits may function to reduce the sounds of hovering, with implications for bioinspiration.

Paint it black: first record of melanism in Canada lynx (Lynx canadensis)

Abstract Variation in coat colour within mammal species is of enduring interest, likely because of its potential to be either adaptive or maladaptive. Coat colour in the genus Lynx tends to be stable, with little variation within species compared to that of other felids. Canada lynx (Lynx canadensis) have coats that typically are silver grayish in winter and reddish brown in summer with dark spots, and black hairs on the tips of their tails and ears. A rare pallid colourmorph is occasionally observed, suggestive of partial albinism. Here, I report the first record of a melanistic Canada lynx. The individual was photographed during summer in the Yukon (Canada). It had a black coat containing whitish gray guard hairs throughout, as well as whitish gray hairs in the facial ruff and the rostrum and dorsal regions. There are only a small number of records of coat colour polymorphisms in the genus Lynx. The adaptive significance of melanism in lynx is unknown, but the loss of camouflage when hunting during winter is likely maladaptive.

Quiet flight, the leading edge comb, and their ecological correlates in owls (Strigiformes)

Abstract Owls have evolved sensitive hearing facilitated by a facial disc, and flight that is quieted in part by a leading-edge comb on their wing. This comb is a series of modified barbs, or serrations, which project up from the outermost primary feathers on the leading edge of the wing. Here we explore the evolution of comb and facial disc morphology. We measured leading-edge comb morphology on museum skins of 147 owl species, and facial disc morphology from photos, as well as ecological traits, on 66 species. The first principal component of comb morphology loaded on serration length, which varied between 0 and ~6 mm long in the species we sampled. Comb size (PC1) was correlated with relative facial disc size, suggesting that owls with good hearing also tend to have quiet flight. Two non-exclusive hypotheses for why quiet flight evolved are for stealth, allowing the owl to approach prey undetected; or to reduce self-masking, enabling the owl to hear prey better midflight. We examined whether ecological variables (prey type, active period and habitat) suggest whether stealth or self-masking better explain the evolution of comb size. Phylogenetic analyses suggested support for both the stealth and the self-masking hypotheses for the evolution of quiet flight.

The possible occurrence of cranial asymmetry in three harrier (Accipitridae: Circus) species

Abstract The harriers (Accipitridae: Circus) represent a unique group of raptorial birds due to their hunting behaviour and their facial ruff and prominent facial disc. During previous studies it was suggested that harrier species may have other convergent features shared with owls like asymmetric or enlarged ear openings related to sensitive hearing capabilities. In this study, cranial asymmetry was done using SAGE (Symmetry and Asymmetry of Geometric Data) software. 32 skulls of 3 species (Western Marsh Harrier (Circus aeruginosus) n=8, Montagu’s Harrier (Circus pygargus) n=10, Hen Harrier (Circus cyaneus) n=14) were photographed, digitized and assigned with 2D landmarks with TpsDig software. The variables were analysed based on Generalized Procrustes analysis. The morphometric data showed cranial asymmetry of harriers. This asymmetry should rather be explained by foraging strategies as the results are corresponding to the exceptionally good hearing of these species among diurnal raptors.

Sex identification comparison of barn owls (Tyto alba javanica) using morphological features and molecular-based methods

Abstract Sexing of barn owls, Tyto alba javanica, using morphological traits has not been accurate enough due to ambiguous sexual dimorphism between sexes. This has been one of the major problems for the management of barn owls worldwide, especially for translocation and captive-breeding programs. In order to increase the success rate of sexing the barn owl, we compared the results of a molecular sexing method to six morphological traits for sexing the owls: the shape and colour of the facial disc, the colour of the throat area, the tail plumage, the colour of their tarsus, the back plumage, and the frequency of spotting on the chest and underside of the wings. The result of our comparison showed that sex identification using morphological traits had an accuracy of only 72.7%. Three of our samples were identified as females using morphological traits, but molecular sexing determined that these samples were males. We also used our results to determine the best morphological traits for sexing barn owls, and concluded that the best traits for morphological sexing are the frequency of spotting on the chest and underparts of barn owls (accuracy of 81.8%), as well as colour of the owls’ facial disc and throat area (accuracy of 63.6%).

Table Books

Book Review| September 01 2018 Table Books The Enigma of the Owl: An Illustrated Natural History. By Mike Unwin and David Tipling. 2016. Yale University Press. (ISBN 9780300222739). 288 pp. Hardcover, $40. The American Biology Teacher (2018) 80 (7): 546–547. https://doi.org/10.1525/abt.2018.80.7.546b Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Table Books. The American Biology Teacher 1 September 2018; 80 (7): 546–547. doi: https://doi.org/10.1525/abt.2018.80.7.546b Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe American Biology Teacher Search It is a rare lover of the natural world who can resist the beauty, elegance, and … well … the enigma of owls. And thus, inherently, there are few who will be able to resist the fascination, charm, and beauty of this lovely book. Oversized and lavish, with exquisite photographs, The Enigma of the Owl brings the owls of the world to life in front of your eyes. The book opens with a short introduction examining both the history and the natural history of owls. A discussion of owls as a group informs the reader of the two owl families and surveys both living and prehistoric species (including an extinct barn owl that stood a meter tall). Basic general owl anatomy is described – distinguished, in particular, by large eyes for binocular vision while hunting and, less obviously, by keen hearing, aided by the distinctive feathered facial disc of most... You do not currently have access to this content.

Combination of Interaural Level and Time Difference in Azimuthal Sound Localization in Owls.

A function of the auditory system is to accurately determine the location of a sound source. The main cues for sound location are interaural time (ITD) and level (ILD) differences. Humans use both ITD and ILD to determine the azimuth. Thus far, the conception of sound localization in barn owls was that their facial ruff and asymmetrical ears generate a two-dimensional grid of ITD for azimuth and ILD for elevation. We show that barn owls also use ILD for azimuthal sound localization when ITDs are ambiguous. For high-frequency narrowband sounds, midbrain neurons can signal multiple locations, leading to the perception of an auditory illusion called a phantom source. Owls respond to such an illusory percept by orienting toward it instead of the true source. Acoustical measurements close to the eardrum reveal a small ILD component that changes with azimuth, suggesting that ITD and ILD information could be combined to eliminate the illusion. Our behavioral data confirm that perception was robust against ambiguities if ITD and ILD information was combined. Electrophysiological recordings of ILD sensitivity in the owl’s midbrain support the behavioral findings indicating that rival brain hemispheres drive the decision to orient to either true or phantom sources. Thus, the basis for disambiguation, and reliable detection of sound source azimuth, relies on similar cues across species as similar response to combinations of ILD and narrowband ITD has been observed in humans.

Development of auditory sensitivity in the barn owl

Adult barn owl hearing is acute, but development of this sense is not well understood. We, therefore, measured auditory brainstem responses in barn owls from before the onset of hearing (posthatch day 2, or P2) to adulthood (P69). The first consistent responses were detected at P4 for 1 and 2kHz, followed by responses to 0.5 and 4kHz at P9, and 5kHz at P13. Sensitivity to higher frequencies increased with age, with responses to 12kHz appearing about 2months after hatching, once the facial ruff was mature. Therefore, these altricial birds achieve their sensitivity to sound during a prolonged period of development, which coincides with maturation of the skull and facial ruff (Haresign and Moiseff in Auk 105:699-705, 1988).

Sex Differences in Long-eared Owl Plumage Coloration

Abstract Most species of owls lack distinctive sexual color dimorphism, and plumage is not considered reliable for distinguishing sex. In North America, Long-eared Owls (Asio otus) are generally considered monomorphic in color, although there are subtle color differences between the sexes. From 1987 to 2015, we investigated differences in plumage coloration of male and female Long-eared Owls in western Montana. We initially used an observational method (1987–1993), followed by a quantitative method (1994–1999), and then a simplified method (2000–2015). When we used the observational method, we correctly sexed all 22 Long-eared Owls. For the quantitative method, we used a Munsell Soil Color Chart to score underwing coverts, tarsometatarsus, and facial disc of breeding males and females and museum specimens purportedly sexed correctly. We found significant sex-specific color differences: underwing coverts (G = 136.77, df = 5, P < 0.01), tarsometatarsus (G = 44.50, df = 4, P < 0.01), and facial disc (G = 50....

A case of partial leucism in the American Barn Owl (Tyto furcata) (Temminck, 1827), from Buenos Aires province, Argentina

The diverse colorations of a birds’ plumage are due to either structural colors or pigments that are synthesized in specialized cells or incorporated through the diet. However, plumage color aberrations can occur; several cases of albinism and leucism have been reported for different bird species and some examples are found in Strigiformes. A specimen of the American Barn Owl (Tyto furcata) with partial leucism was found in Carhué, Buenos Aires province. The plumage of its facial disc, tail and the ventral region was completely white; furthermore, the neck, primaries, and secondaries were pigmented although in a significantly lighter fashion than in normal-phenotype specimens. The rest of the body presented a normal pattern for the species.

Hinterland's Who’s Who: Birding, Multiplicity, and Barn Owls

Hinterland's Who’s Who: Birding, Multiplicity, and Barn Owls

Properties of low-frequency head-related transfer functions in the barn owl (Tyto alba)

The barn owl (Tyto alba) possesses several specializations regarding auditory processing. The most conspicuous features are the directionally sensitive facial ruff and the asymmetrically arranged ears. The frequency-specific influence of these features on sound has consequences for sound localization that might differ between low and high frequencies. Whereas the high-frequency range (>3 kHz) is well investigated, less is known about the characteristics of head-related transfer functions for frequencies below 3 kHz. In the present study, we compared 1/3 octaveband-filtered transfer functions of barn owls with center frequencies ranging from 0.5 to 9 kHz. The range of interaural time differences was 600 micros at frequencies above 4 kHz, decreased to 505 micros at 3 kHz and increased again to about 615 micros at lower frequencies. The ranges for very low (0.5-1 kHz) and high frequencies (5-9 kHz) were not statistically different. Interaural level differences and monaural gains increased monotonically with increasing frequency. No systematic influence of the body temperature on the measured localization cues was observed. These data have implications for the mechanism underlying sound localization and we suggest that the barn owl's ears work as pressure receivers both in the high- and low-frequency ranges.

Improvements of Sound Localization Abilities by the Facial Ruff of the Barn Owl (Tyto alba) as Demonstrated by Virtual Ruff Removal

BackgroundWhen sound arrives at the eardrum it has already been filtered by the body, head, and outer ear. This process is mathematically described by the head-related transfer functions (HRTFs), which are characteristic for the spatial position of a sound source and for the individual ear. HRTFs in the barn owl (Tyto alba) are also shaped by the facial ruff, a specialization that alters interaural time differences (ITD), interaural intensity differences (ILD), and the frequency spectrum of the incoming sound to improve sound localization. Here we created novel stimuli to simulate the removal of the barn owl's ruff in a virtual acoustic environment, thus creating a situation similar to passive listening in other animals, and used these stimuli in behavioral tests.Methodology/Principal FindingsHRTFs were recorded from an owl before and after removal of the ruff feathers. Normal and ruff-removed conditions were created by filtering broadband noise with the HRTFs. Under normal virtual conditions, no differences in azimuthal head-turning behavior between individualized and non-individualized HRTFs were observed. The owls were able to respond differently to stimuli from the back than to stimuli from the front having the same ITD. By contrast, such a discrimination was not possible after the virtual removal of the ruff. Elevational head-turn angles were (slightly) smaller with non-individualized than with individualized HRTFs. The removal of the ruff resulted in a large decrease in elevational head-turning amplitudes.Conclusions/SignificanceThe facial ruff a) improves azimuthal sound localization by increasing the ITD range and b) improves elevational sound localization in the frontal field by introducing a shift of iso–ILD lines out of the midsagittal plane, which causes ILDs to increase with increasing stimulus elevation. The changes at the behavioral level could be related to the changes in the binaural physical parameters that occurred after the virtual removal of the ruff. These data provide new insights into the function of external hearing structures and open up the possibility to apply the results on autonomous agents, creation of virtual auditory environments for humans, or in hearing aids.

Influence of the facial ruff on the sound-receiving characteristics of the barn owl’s ears

The barn owl, a nocturnal predator, derives its German name ("Schleiereule", direct English translation "veil owl") from the conspicuous ruff that covers the ear openings and gives the head a face-like appearance. The ruff is a specialization for the perception of sound. The densely-ramified reflector feathers forming the border of the ruff direct sound to the ear-openings. We studied the influence of the ruff on the behaviorally relevant sound-localization parameters interaural time difference (ITD) and interaural level difference (ILD). The directionality of the ear was much greater when the ruff was intact than when the reflector feathers were removed. With ruff intact, the distribution of ILDs was oblique and the maximum ITD occurred around 110 degrees of azimuth. When all head feathers were removed, the steepest ILD gradient was much closer to the horizontal axis and ITD was maximal at 90 degrees . Many effects were frequency specific. Thus, the ruff reflects some properties of the human pinna. However, by shifting the point where ITD becomes maximal beyond 90 degrees , the ruff also introduces a break of the front-back symmetry of ITD.

Morphometry of auricular feathers of barn owls (Tyto alba).

In all owl species, the facial plumage forms a parabolic dish, the facial ruff, which is most conspicuous in the the barn owl (Tyto alba). The center of the ruff is formed by auricular feathers. Such feathers are also found on the preaural flaps which cover the ear openings, and in the region of the beak. In this study, we compare the different types of auricular feathers of the barn owl with contour feathers from the neck. Auricular feathers are characterised by an open vane structure and fewer barbs as compared to contour feathers. Auricular feathers also have fewer distal and proximal barbules than contour feathers. The open vane of the auricular feather results from an acute angle between the barb and the basis of the barbules, and from the extension of the pennula parallel to the barbs. These reductions are differently expressed in the three different types of auricular feathers investigated here and correspond with their function (protecting the ruff from dust).

Tonotopic and Somatotopic Representation in the Nucleus basalis of the Barn Owl, Tyto alba

We have investigated the somatosensory and auditory representations in the nucleus basalis of the barn owl. In pigeons and finches, the nucleus basalis contains a representation of the beak and an auditory area. In the barn owl, the nucleus basalis also contains a complete somatotopic map of the head and body (as in the budgerigar), with a tonotopically organized auditory area in close proximity to the representation of the facial ruff and the preaural area. Recordings within and around the nucleus basalis revealed predominantly (about 80%) contralateral responses to somatic stimulation. The somatotopic map was oriented with the head down and rostral. Penetrations revealed an over-representation of the feet in dorsal basalis, followed by the rest of the body and wings more ventrally. Towards more rostral positions in nucleus basalis, responses from the head and beak predominated ventrally. The auditory response area was encountered below the region that responded to stimulation of the facial ruff and preaural flap regions and above a region responsive to beak stimulation. Auditory responses were tonotopically organized, with low best frequencies dorsal. Some penetrations yielded predominantly monaural responses with a fairly broad dynamic range, similar to those recorded from the ventral nucleus of the lateral lemniscus (LLV) and the cochlear nucleus angularis, whereas other penetrations contained predominantly binaural responses sensitive to interaural time differences (ITD). The physiological responses could be predicted on the basis of auditory projections to the nucleus basalis. An injection of biotinylated dextran amine (BDA) in the auditory region of nucleus basalis retrogradely labeled cells in both the caudal and rostral parts of the intermediate lateral lemniscal nucleus (LLIc and LLIr), and a few cells in the anterior part of the dorsal lateral lemniscal nucleus (LLDa, previously known as nucleus ventralis lemnisci lateralis, pars anterior, or VLVa) and in the posterior part of the dorsal lateral lemniscal nucleus (LLDp, previously known as nucleus ventralis lemnisci lateralis, pars posterior, or VLVp). A large injection of cholera toxin B-chain (CTB) into the nucleus basalis also produced dense retrograde labeling of a previously unidentified nucleus on the lateral aspect of the rostral pons, that we here call nucleus pontis externus (PE). An injection of CTB into PE produced dense retrograde labeling of the contralateral dorsal column nuclei and anterograde labeling of the ipsilateral lateral and dorsolateral nucleus basalis. Together these results define major somatosensory and auditory projections to the owl telencephalon that bypass the thalamus.

Breeding Biology of Barred Forest-Falcons (Micrastur ruficollis) in Northeastern Guatemala

Little is known about the reproductive biology of most Neotropical raptors (Thiollay 1985). One particularly little-known genus is Micrastur, the forestfalcons, which comprise a group of six species of small to medium-sized falconids that inhabit tropical forests from central Mexico to northern Argentina (Brown and Amadon 1968, del Hoyo et al. 1994). Forest-falcons are characterized by a long tail, short wings, and a slight facial ruff (Brown and Amadon 1968, del Hoyo et al. 1994), which appear to be adaptations to tropical forest environments. Here, we report new information on the breeding biology of the Barred Forest-Falcon (M. ruficollis) in a relatively undisturbed lowland tropical forest in Guatemala. Study area and methods.-We studied Barred ForestFalcons in Tikal National Park, northeastern Guatemala (17?13'N, 89?36'W), from 1988 to 1996. Vegetation in the 576-km2 park is semideciduous tropical forest with rolling hills ranging from 200 to 400 m elevation. Tikal has a pronounced wet and dry season. Rains usually start in May or early June and decrease by December. During our study, monthly precipitation ranged from 1 mm in March 1991 to 302 mm in September 1989. Mean annual rainfall was 1,309 mm from 1988 to 1995 (pers. obs.), and mean monthly temperatures ranged from 15?C in January to 35?C in May from 1989 to 1995. We searched the forest daily from March through July to document activity of potential breeding pairs. Forest-falcons are most active in the morning and evening, and we concentrated our searches to these hours, usually beginning between first light and 0900. We followed pairs by sight and sound until a nest was confirmed by behavior of the birds. When possible, we climbed nest trees to observe eggs or young in cavities, sometimes with the aid of a flashlight. Nest observations totaled more than 1,800 h, most of which occurred during the breeding seasons of 1989 through 1992, with incidental observations from 1993 to 1995 and for four weeks in 1996. For each nest, we determined laying date, clutch size, hatching success (by periodic checks of nest cav-

Book ReviewsEthnography at the Edge: Crime, Deviance, and Field Research. Edited by Jeff Ferrell and Mark S. Hamm. Boston: Northeastern University Press, 1998. Pp. xviii+309. $55.00 (cloth); $22.50 (paper).

Previous articleNext article No AccessBook Reviews Ethnography at the Edge: Crime, Deviance, and Field Research. Edited by Jeff Ferrell and Mark S. Hamm. Boston: Northeastern University Press, 1998. Pp. xviii+309. $55.00 (cloth); $22.50 (paper).Sudhir Venkatesh Sudhir VenkateshHarvard University Search for more articles by this author Harvard UniversityPDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by American Journal of Sociology Volume 105, Number 1July 1999 Article DOIhttps://doi.org/10.1086/210296 Views: 17Total views on this site Citations: 2Citations are reported from Crossref Permission to reprint a book review in this section may be obtained only from the review's author.PDF download Crossref reports the following articles citing this article:Scott Jacques, Richard Wright Dangerous Intimacy: Toward a Theory of Violent Victimization in Active Offender Research, Journal of Criminal Justice Education 21, no.44 (Dec 2010): 503–525.https://doi.org/10.1080/10511253.2010.516567Mark von Campenhausen, Hermann Wagner Influence of the facial ruff on the sound-receiving characteristics of the barn owl’s ears, Journal of Comparative Physiology A 192, no.1010 (May 2006): 1073–1082.https://doi.org/10.1007/s00359-006-0139-0

The use of IR thermography to measure the radiative temperature and heat loss of a barn owl ( Tyto alba)

Infrared (IR) thermography was used to identify the major sites of heat loss from a female barn owl at an air temperature of 17.6°C. When perched, the mean radiative temperature of the owl was 21.1°C (SD=3.5). The facial disc averaged 23.9°C (SD=9.1) and the temperature of the eyes was greater than 33°C. Images showed an area on the lower abdomen that was warmer than 27°C. During flight, the temperature of plumage overlying wing muscles was more than 30°C. The metabolic heat production of the barn owl was estimated to be 42 W m −2 (1.68 W) at 17.6°C which agreed with previous measurements of metabolism. Heat loss from the head was almost double that from the body as a whole, indicating the importance of reducing exposure of the head during roosting. The metabolic rate during flight was calculated to be 13×BMR ( Pennycuick, 1989). This suggested that barn owls lose considerable amounts of heat during prolonged periods of flight. It is hypothesised that by being active in cool nocturnal conditions, barn owls may exploit waste metabolic heat for thermoregulation.