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At least 73 records · Page 4Linked to original sources
PubMed2006

Killing of a pearl-spotted owlet (Glaucidium perlatum) by male red colobus monkeys (Procolobus tephrosceles) in a forest fragment near Kibale National Park, Uganda.

Adult male red colobus (Procolobus tephrosceles) were observed capturing and killing an owl (Glaucidium perlatum) in the Rurama forest fragment near Kibale National Park in western Uganda. The owl was not subsequently eaten by the colobus, their conspecifics, or the other primates present during the attack. Because the incident was preceded by an agonistic encounter with a raptor, the event is best interpreted as a misdirected antipredator behavior. Although antipredator behaviors are not unknown in red colobus, this is the first such incident directed against a raptor to be documented.

Animals↗
PubMed2003

Anatomical markers for the subdivisions of the barn owl's inferior-collicular complex and adjacent peri- and subventricular structures.

The anatomy of the inferior-collicular complex of the barn owl, situated below the fourth ventricle in the tectal lobe, was studied by determining the distribution of antigens with antibodies directed against tyrosine hydroxylase, gamma-aminobutyric acid (GABA)(Abeta), dopamine- and cyclic AMP-regulated phosphoprotein (DARPP-32), calretinin, and calbindin. Additionally, the somata were stained with cresyl violet, and fibers were marked according to the Gallyas procedure. These markers were chosen to allow for an easy delineation of the boundaries between the subnuclei of the inferior colliculus. We could discriminate eight structures that belong to the three subnuclei of the inferior colliculus [the central nucleus (ICC), the superficial nucleus (ICS), the external nucleus (ICX)] and to the optic tectum. Periventricular tectal layers 15a and 15b stained well with all the antibodies used. The ICS, embedded in tectal layer 15a, may be divided into a dorsal and a ventral lamina. It does not have direct contact with the other nuclei of the inferior colliculus. The border between tectal layer 15a and ICX was well marked by all antibodies, but less so in Gallyas and cresyl violet stains. The ICC consists of a core and a medial and lateral shell. The core was clearly demarcated with antibodies against calretinin and calbindin. The border between the lateral shell and the ICX was marked less well than the borders between ICX and 15a, but the somata were much more darkly labeled with the DARPP-32 antibody in ICX than in the lateral shell of ICC. None of the markers delineated the border between the medial and lateral shell of ICC.

Animals↗
PubMed2003

Development of output connections from the inferior colliculus to the optic tectum in barn owls.

We studied the development of the projection from the external nucleus of the inferior colliculus (ICX) to the optic tectum (OT) in the barn owl. The projection was labeled by tracer application in vitro to either the OT or the ICX, or by staining ICX cells intracellularly with biocytin. The axons of ICX neurons bifurcated into an ascending branch that projected toward the OT and a descending branch that coursed caudally to an unknown target in the brainstem. Axons of the ICX were observed to grow into the OT from embryonic day 16 (E16) on. From E22 on, side branches of the axonal projections could be found within the OT. At the day of hatching (E32), the projection displayed a dorsoventral topography comparable to the adult owl; however, atopically projecting cells remained. The complexity of the axonal arborization in the adult barn owl was found to be slightly increased compared with the hatchling. The terminal area of individual ICX cells in the OT of the adult barn owl was still broad, a finding that had not been expected from the sharply defined physiological response properties of the bimodal neurons in the space map of the OT. However, the width of the termination zone was in accordance with the large dendritic tree of the adult ICX cells, because both spanned comparable angles in their respective maps. Our data suggest that a coarse projection from the ICX to the OT can develop without coherent sensory input and may, therefore, be innately determined.

Aging↗
PubMed2004

Low density of membrane particles in auditory hair cells of lizards and birds suggests an absence of somatic motility.

Hair cells are the mechanoreceptive cells of the vertebrate lateral line and inner ear. In addition to their sensory function, hair cells display motility and thus themselves generate mechanical energy, which is thought to enhance sensitivity. Two principal cellular mechanism are known that can mediate hair-cell motility in vitro. One of these is based on voltage-dependent changes of an intramembrane protein and has so far been demonstrated only in outer hair cells of the mammalian cochlea. Correlated with this, the cell membranes of outer hair cells carry an extreme density of embedded particles, as revealed by freeze fracturing. The present study explored the possibility of membrane-based motility in hair cells of nonmammals, by determining their density of intramembrane particles. Replicas of freeze-fractured membrane were prepared from auditory hair cells of a lizard, the Tokay gecko, and a bird, the barn owl. These species were chosen because of independent evidence for active cochlear mechanics, in the form of spontaneous otoacoustic emissions. For quantitative comparison, mammalian inner and outer hair cells, as well as vestibular hair, cells were reevaluated. Lizard and bird hair cells displayed median densities of 2,360 and 1,880 intramembrane particles/microm2, respectively. This was not significantly different from the densities in vestibular and mammalian inner hair cells; however, it was about half the density in of mammalian outer hair cells. This suggests that nonmammalian hair cells do not possess high densities of motor protein in their membranes and are thus unlikely to be capable of somatic motility.

Animals↗
PubMed2005

Distribution within the barn owl's inferior colliculus of neurons projecting to the optic tectum and thalamus.

Behavioral studies in barn owls indicate that both the optic tectum (OT) and the auditory arcopallium (AAr) mediate sound localization through the presence of neurons that respond only when sound comes from a circumscribed direction in space. The early stages of the computations leading to these so-called space-specific neurons are shared in a common brainstem pathway, which then splits at the level of the inferior colliculus (IC) such that the last computational stage is thought to be duplicated. The study presented here addresses whether the space-specific neurons in OT and AAr are indeed partially independent of each other by using anatomical methods more precise than those used in previous studies. Specifically, projection neurons in IC were retrogradely labelled with injections of fluorescein- and rhodamine-conjugated dextran amines into OT and nucleus ovoidalis (OV), the thalamic nucleus leading to AAr. By labelling the OT-projecting and OV-projecting neurons in the same owl, it was confirmed that neurons in IC project to either OV or OT but not both. However, although a segregation was generally observed between the medially positioned OV-projecting neurons and the laterally positioned OT-projecting neurons, there was also a slight overlap between the two populations. Moreover, electrolytic lesions demarcating physiological tuning properties indicate that many OV-projecting neurons are within the area containing space-specific neurons. These results highlight the need for more detailed studies elucidating the microcircuitry and corresponding physiology of IC, such as have been done in the cortices of the mammalian cerebellum and cerebrum.

Animals↗
PubMed2005

Embryonic and posthatching development of the barn owl (Tyto alba): reference data for age determination.

The normal development of the barn owl was documented with the intent of providing a guideline for determining the maturational stage of embryos and posthatching individuals. Embryonic development up to stage 39 could be well described using the well-known developmental atlas for the chicken (Hamburger and Hamilton [1951] J. Morphol. 88:49-92). For later stages, limb size was established as a suitable indicator. In addition, measuring the egg's vascularized area through candling was found to be a useful, noninvasive method for staging very early embryos, up to stage 25. An average relationship between incubation period and embryonic stage was derived, which showed that development in the barn owl initially lags that in the chicken. For posthatching individuals, skeletal measures (tarsal and ulnar length, skull width and length) were the most reliable parameters for judging maturation, up to 1 month. For older individuals, feather development (e.g., length of primary wing feathers) provided the only cue.

Age Factors↗
PubMed2003

Localization of KCNC1 (Kv3.1) potassium channel subunits in the avian auditory nucleus magnocellularis and nucleus laminaris during development.

The KCNC1 (previously Kv3.1) potassium channel, a delayed rectifier with a high threshold of activation, is highly expressed in the time coding nuclei of the adult chicken and barn owl auditory brainstem. The proposed role of KCNC1 currents in auditory neurons is to reduce the width of the action potential and enable neurons to transmit high frequency temporal information with little jitter. Because developmental changes in potassium currents are critical for the maturation of the shape of the action potential, we used immunohistochemical methods to examine the developmental expression of KCNC1 subunits in the avian auditory brainstem. The KCNC1 gene gives rise to two splice variants, a longer KCNC1b and a shorter KCNC1a that differ at the carboxy termini. Two antibodies were used: an antibody to the N-terminus that does not distinguish between KCNC1a and b isoforms, denoted as panKCNC1, and another antibody that specifically recognizes the C terminus of KCNC1b. A comparison of the staining patterns observed with the panKCNC1 and the KCNC1b specific antibodies suggests that KCNC1a and KCNC1b splice variants are differentially regulated during development. Although panKCNC1 immunoreactivity is observed from the earliest time examined in the chicken (E10), a subcellular redistribution of the immunoproduct was apparent over the course of development. KCNC1b specific staining has a late onset with immunostaining first appearing in the regions that map high frequencies in nucleus magnocellularis (NM) and nucleus laminaris (NL). The expression of KCNC1b protein begins around E14 in the chicken and after E21 in the barn owl, relatively late during ontogeny and at the time that synaptic connections mature morphologically and functionally.

Animals↗
PubMed2000

A generalized fecal glucocorticoid assay for use in a diverse array of nondomestic mammalian and avian species.

Noninvasive fecal glucocorticoid analysis has tremendous potential as a means of assessing stress associated with environmental disturbance in wildlife. However, interspecific variation in excreted glucocorticoid metabolites requires careful selection of the antibody used in their quantification. We compared four antibodies for detecting the major fecal cortisol metabolites in yellow baboons following (3)H cortisol administration, ACTH challenge, and HPLC separation of fecal glucocorticoid metabolites. The most effective antibody (ICN corticosterone RIA; Cat. No. 07-120102) demonstrated relatively high cross-reactivities to the major cortisol metabolites present in feces during peak excretion, following both radiolabel infusion and ACTH challenge. This same antibody also detected increased fecal glucocorticoid metabolites after ACTH administration in the African elephant, black rhinoceros, Roosevelt elk, gerenuk, scimitar-horned oryx, Alaskan sea otter, Malayan sun bear, cheetah, clouded leopard, longtailed macaque, and northern spotted owl. Results suggest that (1) fecal glucocorticoid assays reliably detect endogenous changes in adrenal activity of a diverse array of species and (2) where comparisons were made, the ICN corticosterone antibody generally was superior to other antibodies for measuring glucocorticoid metabolites in feces.

Adrenocorticotropic Hormone↗
PubMed2002

A dynamic model for intertemporal allocation of old-growth forests in the Pacific Northwest.

Across the globe, continued policy debates regarding the management of old-growth forests center around the difficult task of balancing economic and ecological considerations. Though the forests of the Pacific Northwest United States are among the most studied old-growth ecosystems, ecological and economic analyses have yielded public land management directives that remain controversial. Specifically, the recently adopted Northwest Forest Plan lacks explicit goals for maintaining intergenerational equity for the use of forest resources and the diversity of old-growth ecosystems. Unlike previous studies which rely on monetary quantification of costs and benefits, this study develops and applies a conceptual framework for evaluating socially optimal Pacific Northwest old-growth forest utilization strategies. Conditions for the optimal management of old-growth forests are derived using dynamic programming. The objective function synthesizes relevant biological and economic attributes of the old-growth allocation problem. Results in the form of extraction paths are compared given social pressure for consumptive and non-consumptive benefits, as well as different planning horizons, rates of social time preference, and environmental variance. Lengthening the planning horizon results in a vast divergence of optimal policies in the absence of discounting. Extraction rates appear to approach zero as the planning horizon approaches infinity. While higher rates of social time preference increase the rate of extraction, forest stocks remaining at the terminal time period equal levels remaining with a lower discount rate. Increasing environmental variance results in a higher level of stock remaining at the terminal time period. This analysis, while specific to the old-growth controversy of the Pacific Northwest, does provide general guidelines for addressing similar problems of multiple uses of natural areas, particularly where such uses are mutually incompatible, or where one use may be irreversibly destructive to another.

Animals↗
PubMed2006

A link between eumelanism and calcium physiology in the barn owl.

In many animals, melanin-based coloration is strongly heritable and is largely insensitive to the environment and body condition. According to the handicap principle, such a trait may not reveal individual quality because the production of different melanin-based colorations often entails similar costs. However, a recent study showed that the production of eumelanin pigments requires relatively large amounts of calcium, potentially implying that melanin-based coloration is associated with physiological processes requiring calcium. If this is the case, eumelanism may be traded-off against other metabolic processes that require the same elements. We used a correlative approach to examine, for the first time, this proposition in the barn owl, a species in which individuals vary in the amount, size, and blackness of eumelanic spots. For this purpose, we measured calcium concentration in the left humerus of 85 dead owls. Results showed that the humeri of heavily spotted individuals had a higher concentration of calcium. This suggests either that plumage spottiness signals the ability to absorb calcium from the diet for both eumelanin production and storage in bones, or that lightly spotted individuals use more calcium for metabolic processes at the expense of calcium storage in bones. Our study supports the idea that eumelanin-based coloration is associated with a number of physiological processes requiring calcium.

Animals↗
PubMed2000

Supercritical fluid extraction of polycyclic aromatic hydrocarbons from liver samples and determination by HPLC-FL.

An extraction/clean-up procedure by SFE was developed for isolating PAHs from liver samples for subsequent HPLC-FL determination of ten PAHs in the enriched extract. Recoveries (90-115%) and RSD % (< or =7.7) were satisfactory. When applied to 11 samples of bird of prey (Tyto alba) protected species and classified of special interest, from the Galicia (Northwest to Spain), benzo[ghi]perylene and indeno[1,2,3-cd]pyrene were undetectable; chrysene and benzo[a]pyrene are only detected in one sample; benzo[a]anthracene and benzo[k]fluoranthene are only quantified in one sample and benzo[b]fluoranthene in two samples. The other PAHs, anthracene, fluoranthene and pyrene are present in almost all the samples.

Animals↗
PubMed2005

A risk assessment approach to DDE exposure based on the case of the eastern screech-owl (Megascops asio) in apple orchards of southern Quebec,Canada.

As part of a larger study assessing exposure of the Eastern screech-owl to pesticides in apple orchards from consumption of contaminated small-mammal prey, we evaluated the potential for owls in orchards of southern Quebec to be exposed to persistent contaminants with emphasis on DDE. Levels were highest in short-tailed shrews (0.94 to 26.29 microg/g wet wt). Based on a worst-case scenario, it is possible that consumption of small-mammal prey in orchards of the study area may result in exposure to DDE at a level associated with significant eggshell thinning; however, consumption of other prey, (e.g., robins) may represent a more important threat. Other organochlorines and persistent contaminants such as trace metals and PCBs, reported elsewhere, were found at negligible levels only. Based on an evaluation of the data used, we identify critical information required to enhance the proposed risk assessment.

Animals↗
PubMed2004

Effectiveness of voluntary habitat stewardship in conserving grassland: case of operation burrowing owl in Saskatchewan.

There have been no published performance evaluations of nongovernmental, voluntary habitat stewardship programs. The Operation Burrowing Owl (OBO) stewardship program, initiated in 1987, was evaluated for its effectiveness in conservation of grassland habitat during 1986-1993. The 108 OBO sites from 1987 to 88 and 98 randomly selected non-OBO sites that were grassland in 1986 in the Regina-Weyburn, Saskatchewan study area were classified by size and agricultural soil suitability. By 1993, 41 (38%) of the 108 OBO sites had been withdrawn from the program. The 1986 area of grassland was compared with grassland area calculated from digitized 1993 LANDSAT imagery. A correction for satellite inaccuracies was determined. Grassland retention in 1993 was significantly higher at OBO sites (66%) than at random sites (49%), demonstrating that the OBO voluntary program effectively conserved habitat. Also, grassland retention was significantly lower on sites with better agricultural soils, and for sites <12 ha in size. Site type (OBO or random), size and their interaction, followed by agricultural soil suitability, had the greatest effects on grassland retention. During an era of accelerated grassland loss, OBO strongly and positively (statistically significant) affected conservation of grassland sites most at risk: sites <12 ha in size and with good to excellent agricultural soils. This suggests that grassland conservation efforts focus on vulnerable sites (small size and/or good agricultural soils) to provide nesting habitat for burrowing owls. Our study demonstrates that a voluntary stewardship program can significantly increase conservation of habitat.

Agriculture↗
PubMed2002

Temporal modulation transfer functions in the barn owl (Tyto alba).

Barn owls (Tyto alba) have evolved several specializations in their auditory system to achieve the high sensory acuity required for prey capture, including superior processing of interaural time differences and phase coding in the auditory periphery. Here, we tested whether barn owls are capable of high temporal resolution that may be a prerequisite for the accuracy in binaural processing. Temporal resolution was measured psychoacoustically and demonstrated in temporal modulation transfer functions. Four barn owls were trained in an operant task with food reward to detect sinusoidal amplitude modulations within an 800-ms gated white-noise burst or 800-ms periods of modulation in continuous white noise (spectrum levels of -5 dB and 15 dB SPL). Within the range of tested amplitude modulation frequencies from 5 Hz to 1280 Hz, barn owls' detection thresholds were lowest at 10-20 Hz. This sensitivity corresponds to an intensity-difference limen of between 0.9 dB and 1.4 dB. For all conditions, temporal modulation transfer functions showed band-pass characteristics with a high-frequency cutoff in the range of 37 Hz to 92 Hz, corresponding to minimum integration times of 4.3 ms and 1.7 ms, respectively. In summary, these data indicate a temporal resolution in the owl's auditory system that is good, but not unusual, compared to other vertebrates.

Animals↗
PubMed2002

Depth generalization from stereo to motion parallax in the owl.

Although many sources of three-dimensional information have been isolated and demonstrated to contribute independently, to depth vision in animal studies, it is not clear whether these distinct cues are perceived to be perceptually equivalent. Such ability is observed in humans and would seem to be advantageous for animals as well in coping with the often co-varying (or ambiguous) information about the layout of physical space. We introduce the expression primary-depth-cue equivalence to refer to the ability to perceive mutually consistent information about differences in depth from either stereopsis or motion-parallax. We found that owls trained to detect relative depth as a perceptual category (objects versus holes) when specified by binocular disparity alone (stereopsis), immediately transferred this discrimination to novel stimuli where the equivalent depth categories were available only through differences in motion information produced by head movements (observer-produced motion-parallax). Motion-parallax discrimination did occur under monocular viewing conditions and reliable performance depended heavily on the amplitude of side-to-side head movements. The presence of primary-depth-cue equivalence in the visual system of the owl provides further conformation of the hypothesis that neural systems evolved to detect differences in either disparity or motion information are likely to share similar processing mechanisms.

Animals↗