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PubMed2006

Detection of interaural correlation by neurons in the superior olivary complex, inferior colliculus and auditory cortex of the unanesthetized rabbit.

A critical binaural cue important for sound localization and detection of signals in noise is the interaural time difference (ITD), or difference in the time of arrival of sounds at each ear. The ITD can be determined by cross-correlating the sounds at the two ears and finding the ITD where the correlation is maximal. The amount of interaural correlation is affected by properties of spaces and can therefore be used to assess spatial attributes. To examine the neural basis for sensitivity to the overall level of the interaural correlation, we identified subcollicular neurons and neurons in the inferior colliculus (IC) and auditory cortex of unanesthetized rabbits that were sensitive to ITDs and examined their responses as the interaural correlation was varied. Neurons at each brain level could show linear or non-linear responses to changes in interaural correlation. The direction of the non-linearities in most neurons was to increase the slope of the response change for correlations near 1.0. The proportion of neurons with non-linear responses was similar in subcollicular and IC neurons but increased in the auditory cortex. Non-linear response functions to interaural correlation were not related to the type of response as determined by the tuning to ITDs across frequencies. The responses to interaural correlation were also not related to the frequency tuning of the neuron, unlike the responses to ITD, which broadens for neurons tuned to lower frequencies. The neural discriminibility of the ITD using frozen noise in the best neurons was similar to the behavioral acuity in humans at a reference correlation of 1.0. However, for other reference ITDs the neural discriminibility was more linear and generally better than the human discriminibility of the interaural correlation, suggesting that stimulus rather than neural variability is the basis for the decline in human performance at lower levels of interaural correlation.

Animals↗
PubMed2006

Lentoid bodies in the avian retina.

In-vitro studies suggest that, in avian retina, lentoid bodies arise from Müller cells or developing neuroretina. This report describes lentoid bodies in adult avian retinas in association with retinal trauma or degeneration. Retinal lentoids were identified in four birds (three owls and one parrot) in the course of routine diagnostic histopathology. Sections were stained with periodic acid-Schiff for the purposes of descriptive histology, and immunolabelled for a Müller cell marker (glial fibrillary acidic protein; GFAP) and a lens-specific marker (crystallin alpha-A). Intraretinal lentoids of varying size were identified, the constituent cells resembling bladder cells similar to those seen in cataracts. The process of lentoid formation followed a consistent pattern, characterized by progressive Müller cell hypertrophy in damaged areas, culminating in lentoid formation. GFAP immunoreactivity was strongest in Müller cells in the early stages of hypertrophy and receded as Müller cell hypertrophy advanced and lentoids developed. In contrast to GFAP immunoreactivity, crystalline alpha-A labelling increased in distribution and intensity as Müller hypertrophy became more prominent and lentoids were formed. This represents the first report of intraretinal lentoids in birds in vivo. The immunohistochemical data suggest that they arise from Müller cells. Association of lentoids with retinal damage supports the assertion that they arise following disruption of normal cell-cell communication.

Animals↗
PubMed2005

40K, 137Cs, 90Sr, 238,239+240Pu and 241Am in mammals' skulls from owls' pellets and owl skeletons in Poland.

Skulls of small mammals belonging to two species of rodents and three species of insectivores collected in Eastern Poland were the subject of the present investigation. The skulls were separated from owl pellets. Activities of 40K, 137Cs, 90Sr, 238,239+240Pu and 241Am were determined by means of gamma spectrometry as well as liquid scintillation spectrometry or alpha spectrometry along with relevant radiochemical procedures. A detailed description of the procedures is provided. The research was supplied with the analysis of three skeletons of owls. No measurable difference between the skulls of rodents and insectivorous animals with regard to activity of any of the examined radionuclides was found. No accumulation effect in the owl skeletons was detected. Though measured activities of 137Cs and 40K for the skulls were of the same magnitude as those found previously for large wild herbivorous animals from typical locations in Poland, those for 90Sr were even lower than previously determined. A big difference was found for activities of plutonium and americium isotopes. Their mean activities were higher by an order of magnitude when compared to the examined previously values. The maximum 239+240Pu activity was equal to 97.5+/-7.7 mBq/kg, with 65% of it originating from global fallout. Relatively high content of transuranic elements found for rodents and insectivorous mammals seems to be unrelated to their feeding habits and should rather be attributed to the living conditions. It is suggested that small mammals, together with tiny soil particles present in mid-soil living tunnels, can inhale the transuranic elements.

Americium↗
PubMed2005

The palaeoecology of the micromammals from the late middle Pleistocene site of Hoedjiespunt 1 (Cape Province, South Africa).

The palaeontological site of Hoedjiespunt 1 (HDP1) represents a fossilized hyaena lair. A rich mammalian fauna, including four hominid teeth, has been recovered from the site. Micromammals were recovered from the same sediments as the larger fauna. Taphonomic analysis suggests that the micromammal assemblages from HDP1 were accumulated by a barn owl. The barn owl produces micromammal assemblages that provide a broad sample of micromammals, within a certain size range, living in the hunting area of the owl. There are size-related and other biases inherent in the prey selection of this predator, and owls may roost in one area and hunt in another however, the barn owl has frequently been found to provide a better indication of micromammals living within an area than trapping. The micromammals from HDP1 were used to reconstruct the microhabitats in the vicinity of the site. Two taxonomic habitat indexes were used to assess the environment and dominant habitat types at Hoedjiespunt 1. The variability and adaptability of many of the southern African micromammals complicates interpretation of the results, however, it appears that the micromammals from the HDP1 fossil assemblages utilized habitats of open, scrub vegetation, and rocky and sandy areas. It is suggested that the environment was not markedly different from today, but it may have been relatively more arid. A comparison between HDP1 and other fossil sites in the area dating from the terminal Pleistocene to the Holocene indicates that HDP1 is lacking certain species that are common to all the other west coast fossil sites. There is some discrepancy in the environment indicated by the large mammals as compared that indicated by to the micromammals at the site. It is suggested that this discrepancy may reflect the fact that an owl is likely to have hunted in the vicinity of the hyaena den, probably in the more open areas around the roost site, whereas the macrofauna, accumulated by the further-ranging brown hyaena (Hyaena brunnea), represents environments from further afield.

Animals↗
PubMedDate not supplied

Coding interaural time differences at low best frequencies in the barn owl.

In birds and mammals, precisely timed spikes encode the timing of acoustic stimuli, and interaural acoustic disparities propagate to binaural processing centers. The Jeffress model proposes that these projections act as delay lines to innervate an array of coincidence detectors, every element of which has a different relative delay between its ipsilateral and contralateral excitatory inputs. Thus, interaural time difference (ITD) is encoded into the position of the coincidence detector whose delay lines best cancel out the acoustic ITD. Neurons of the avian nucleus laminaris and mammalian MSO phase-lock to both monaural and binaural stimuli but respond maximally when phase-locked spikes from each side arrive simultaneously, i.e. when the difference in the conduction delays compensates for the ITD. McAlpine et al. [Nat. Neurosci. 4 (2001) 396] identified an apparent difference between avian and mammalian ITD coding. In the barn owl, the maximum firing rate appears to encode ITD. This may not be the case for the guinea pig, where the steepest region of the function relating discharge rate to interaural time delay (ITD) is close to midline for all neurons, irrespective of best frequency (BF). These data suggest that low BF ITD sensitivity in the guinea pig is mediated by detection of a change in slope of the ITD function, and not by maximum rate. We review coding of low best frequency ITDs in barn owls and mammals and discuss whether there may be differences in the code used to signal ITD in mammals and birds.

Acoustic Stimulation↗
PubMedDate not supplied

Bi-sensory, striped representations: comparative insights from owl and platypus.

Bi-sensory striped arrays are described in owl and platypus that share some similarities with the other variant of bi-sensory striped array found in primate and carnivore striate cortex: ocular dominance columns. Like ocular dominance columns, the owl and platypus striped systems each involve two different topographic arrays that are cut into parallel stripes, and interdigitated, so that higher-order neurons can integrate across both arrays. Unlike ocular dominance stripes, which have a separate array for each eye, the striped array in the middle third of the owl tectum has a separate array for each cerebral hemisphere. Binocular neurons send outputs from both hemispheres to the striped array where they are segregated into parallel stripes according to hemisphere of origin. In platypus primary somatosensory cortex (S1), the two arrays of interdigitated stripes are derived from separate sensory systems in the bill, 40,000 electroreceptors and 60,000 mechanoreceptors. The stripes in platypus S1 cortex produce bimodal electrosensory-mechanosensory neurons with specificity for the time-of-arrival difference between the two systems. This "thunder-and-lightning" system would allow the platypus to estimate the distance of the prey using time disparities generated at the bill between the earlier electrical wave and the later mechanical wave caused by the motion of benthic prey. The functional significance of parallel, striped arrays is not clear, even for the highly-studied ocular dominance system, but a general strategy is proposed here that is based on the detection of temporal disparities between the two arrays that can be used to estimate distance.

Animals↗
PubMed2006

Corticosterone is not correlated with nest departure in snowy owl chicks (Nyctea scandiaca).

Snowy owl chicks typically depart from nests at approximately 18 days of age, but 3 weeks before taking their first flight. High concentrations of corticosterone have been implicated in behavioral changes in many species, leading us to assess corticosterone's role in chick nest departure. Corticosterone titers in free-living chicks, however, do not predict this departure event. Baseline corticosterone concentrations decrease as chicks age. By 13 days, corticosterone concentrations are 50% of concentrations in 1-day-old chicks. Baseline concentrations, however, do not differ between departed and nest-bound chicks. Furthermore, corticosterone concentrations become significantly elevated 30min after collecting the baseline sample, indicating that chicks are able to mount a corticosterone response to handling. This stress-induced rise in corticosterone also did not differ between departed and nest-bound chicks. Brood sizes varied, possibly resulting in increased stress in chicks from larger broods. Although many chicks died before reaching departure age, brood sizes at time of nest departure ranged from 1 to 10 chicks. Brood size was not correlated with age of nest departure or individual corticosterone concentrations. These data indicate that it is unlikely that corticosterone plays a role in triggering nest departure in snowy owl chicks.

Animals↗
PubMed2001

Effect of melatonin on circadian rhythm, locomotor activity and body temperature in the intact house sparrow, Japanese quail and owl.

We compared the effect of melatonin on circadian rhythm, body temperature, and locomotion in the intact house sparrow, Japanese quail and owl. Daily treatment with melatonin at a fixed time did not entrain the free-running rhythm of locomotor activity in the house sparrow and the disrupted rhythm in Japanese quail under constant dim light. However, melatonin clearly inhibited movement for several hours after treatment. The duration of resting after injection of melatonin was dose-dependent. Body temperature was significantly decreased after melatonin treatment, the effect being more potent during the active phase than in the resting phase. Although this effect of melatonin on body temperature was also dose-dependent, the magnitude of the decrease in body temperature after injection of melatonin was greater in the house sparrow than in the Japanese quail. On the other hand, melatonin induced a further large decrease of body temperature in a nocturnal bird, the owl, whose pineal gland is degenerate. The decrease of body temperature was larger in the active phase than in the resting phase, and melatonin did not prevent movement in spite of the decrease in body temperature. These results suggest that the effects of melatonin on circadian rhythm, locomotor activity and body temperature differ among avian species, and that these mechanisms may not be linked to each other.

Animals↗
PubMed2003

Orientation mosaic in barn owl's visual Wulst revealed by optical imaging: comparison with cat and monkey striate and extra-striate areas.

Using the technique of intrinsic signal optical imaging, orientation preference maps were obtained from the Wulst of the barn owl in the area that represents central vision, and from the visual cortices (V1 and V2) of cat and marmoset monkey. Iso-orientation domains in barn owl's visual Wulst were patch-like structures with an inter-patch distance of approximately 0.9 mm, arranged in a pinwheel-like manner around singularity points. The size of the iso-orientation domains in barn owl was larger than those found in area V1, but comparable to those found in area V2, of cat and monkey. Superficial layers of the owl visual Wulst may be equivalent to extra-striate visual areas of primates and carnivores, as already suggested by electrophysiologists discussing the much increased radial dimensions of the Wulst compared with neocortex in mammals.

Animals↗
PubMed2003

Bilaterally-projecting efferent neurones to the basilar papilla in the barn owl and the chicken.

The efferent innervation of the auditory basilar papilla of birds and mammals is provided by a dedicated population of brainstem neurones that are separate from those supplying the vestibular organs. This study addresses the question whether a population of bilaterally-projecting efferents, contacting hair cells in both basilar papillae, is consistently present in birds. The chicken and the barn owl were chosen, two species where the total number of efferents was already known and which represent two extremes of an auditory generalist and an auditory specialist, respectively. Fluorogold and Choleratoxin, two potent retrograde tracers, were injected into one cochlear duct each of all individuals. Labelled neurones were subsequently identified in the brainstem using standard fluorescence techniques. A small proportion (up to 2% of the total population) of double-labelled cells was found in both species. The great majority of those double-labelled neurones could be assigned to the ventrolateral group of efferents, which has previously been shown to project exclusively to the auditory basilar papilla. Thus, in birds, like in mammals, a small subgroup of auditory efferents innervates both basilar papillae.

Animals↗
PubMed1999

Phylogenetic analysis of Sarcocystis spp. of mammals and reptiles supports the coevolution of Sarcocystis spp. with their final hosts.

Sequences of the small subunit rRNA genes were obtained for two coccidians, Sarcocystis dispersa and an unnamed Sarcocystis sp. which parasitise the European barn owl and an African viperid snake as their final host, respectively, and share mouse as their intermediate host. Phylogenetic analysis of the sequence data showed that Sarcocystis sp. from the viperid snake is most closely related to another Sarcocystis sp. isolated from an American crotalid snake, while S. dispersa grouped with other bird-transmitted species. The available dataset failed to resolve the evolutionary relationships among four major branches into which all Sarcocystidae and Isospora spp. were split. However, within these branches, the phylogenetic relationships of the majority of analysed members of the genus Sarcocystis reflected coevolution with their final, rather than intermediate hosts.

Animals↗
PubMed2003

Cadmium, chromium and lead contamination of Athene noctua, the little owl, of Bologna and Parma, Italy.

A study was conducted to determine cadmium, chromium and lead concentrations in liver and brain of 52 little owls (Athene noctua) from two provinces of Emilia Romagna region, with the aim of furnishing indirect information concerning contamination of their habitat, also considering possible environmental dispersion of the metals. Metal analysis was performed by atomic absorption spectrophotometry with graphite furnace. Variance analysis with sampling area, gender and age shows that no statistical difference was found for gender, while a significant difference (P<0.05) was found for cadmium and lead, but not for chromium, when sampling areas and age were of concern. For all metals highest mean concentrations were found in liver (170 ppb for cadmium, 297 ppb for chromium and 312 ppb for lead). These levels can be considered as indicative of chronic exposure to low and "background" amounts of pollutants and they are of no toxicological concern, as they are always well below the toxic thresholds defined for each metal. The present study can be considered as a starting point for further analyses, aimed to the definition of any possible subtle effect (e.g. effects on enzymes activity) and of any possible correlation between levels of pollutants and appearance of possible adverse effects. It also furnished useful data for diagnostic cases and potentially for monitoring local contamination.

Animals↗
PubMed2000

Miniature stereo radio transmitter for simultaneous recording of multiple single-neuron signals from behaving owls.

Wireless radiotelemetric transmission of neuronal activity is an elegant technique to study brain-behavior interaction in unrestrained animals. In the current study, a miniature FM-stereo radio transmitter is described that permitted simultaneous recordings from two microelectrodes in behaving barn owls. Input from two independent channels is multiplexed to form a stereo composite signal that modulates a radio frequency carrier. The high quality of broadcasted extracellular signals enabled separation of single units based on differences in spike waveforms. Recording several single cells from different electrodes allows the possibility of investigating correlations between small, distributed neuronal ensembles. Multi-channel radiotelemetry that meets the demands of modern electrophysiology might open a new perspective for combined behavioral/neurophysiological approaches in freely-behaving animals.

Action Potentials↗
PubMed2001

Synthesizing spatially complex sound in virtual space: an accurate offline algorithm.

The study of spatial processing in the auditory system usually requires complex experimental setups, using arrays of speakers or speakers mounted on moving arms. These devices, while allowing precision in the presentation of the spatial attributes of sound, are complex, expensive and limited. Alternative approaches rely on virtual space sound delivery. In this paper, we describe a virtual space algorithm that enables accurate reconstruction of eardrum waveforms for arbitrary sound sources moving along arbitrary trajectories in space. A physical validation of the synthesis algorithm is performed by comparing waveforms recorded during real motion with waveforms synthesized by the algorithm. As a demonstration of possible applications of the algorithm, virtual motion stimuli are used to reproduce psychophysical results in humans and for studying responses of barn owls to auditory motion stimuli.

Acoustic Stimulation↗
PubMed2003

Ecotoxicological suitability of floodplain habitats in The Netherlands for the little owl (Athene noctua vidalli).

This study describes the actual risks of exposure to contaminants, which little owls (Athene noctua vidalli) face in Dutch river floodplains. The results indicate that PCBs pose a risk: not only are levels in little owls from floodplains higher than levels found in little owls from a reference site but the PCB patterns in owls from the floodplains also indicate induction of hepatic cytochrome P450 enzymes by dioxin like compounds, possibly PCBs. Of the heavy metals, only cadmium is thought to pose a risk in certain conditions, for example, when little owls are feeding only on earthworms over a prolonged period of time. The results do not indicate any effects on the occurrence of prey items of the little owl like for instance earthworm, beetles and shrews. Hence, it is not expected that little owls will be affected by diminishing prey availability due to contamination.

Animals↗
PubMed2003

Variation of heavy metals within and among feathers of birds of prey: effects of molt and external contamination.

In this study we examined the effect of external contamination on the heavy metal (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn) concentration in feathers. We compared the heavy metal content among the 10 primary wing feathers of sparrowhawks (Accipiter nisus), little owls (Athene nocta) and barn owls (Tyto alba) and the variation within the outermost tail feather of sparrowhawks and tawny owls (Strix aluco). The concentration of Hg was significantly higher in feathers molted first, suggesting that levels in feathers reflect levels in the blood during formation. For some other elements (Al, Co, Ni, Pb, Zn) on the other hand, there are strong indications that external contamination may have an important impact on the levels detected in the feathers. This should be taken into account in future monitoring studies.

Animals↗
PubMed2002

Manipulation of inhibition in the owl's nucleus laminaris and its effects on optic tectum neurons.

Differences in arrival time and intensity (or level) of sound between the ears serve as cues for localization of sound in many animals. Barn owls use interaural time difference (ITD) and interaural level difference (ILD) for localization in azimuth and elevation, respectively. The owl's brain processes these two cues in separate pathways. The nucleus laminaris is the first site that detects ITDs by methods of delay lines and coincidence detection. The nucleus ventralis lemnisci lateralis, pars posterior is the first site of processing ILDs. The two pathways merge in the inferior colliculus to give rise to sensitivity to combinations of ITD and ILD. This selectivity is relayed to the optic tectum where neurons are sensitive to both visual and auditory stimuli. The present paper reports the results of manipulating inhibition in the nucleus laminaris and its effects on the optic tectum neurons. Injection of GABA or muscimol (a GABA(A) receptor agonist) in the nucleus laminaris reduces the responses of its neurons to ITD. This finding proves that GABA(A) receptor-mediated inhibition acts on the nucleus laminaris neurons. The same treatment did not affect the neurons of the nucleus ventralis lemnisci lateralis, pars posterior, whereas it reduced the response of the optic tectum neurons to ITD-ILD pairs. We conclude that although the two pathways are independent, the process of combining ITD and ILD creates a new relationship in which the output of the neuron varies with the amplitude of either input. This conclusion is consistent with the recent finding that the combination sensitivity is due to a multiplication of ITD and ILD inputs.

Animals↗