Showing papers by "Hermann Wagner published in 2020"

A cortex-like canonical circuit in the avian forebrain

Abstract: Although the avian pallium seems to lack an organization akin to that of the cerebral cortex, birds exhibit extraordinary cognitive skills that are comparable to those of mammals. We analyzed the fiber architecture of the avian pallium with three-dimensional polarized light imaging and subsequently reconstructed local and associative pallial circuits with tracing techniques. We discovered an iteratively repeated, column-like neuronal circuitry across the layer-like nuclear boundaries of the hyperpallium and the sensory dorsal ventricular ridge. These circuits are connected to neighboring columns and, via tangential layer-like connections, to higher associative and motor areas. Our findings indicate that this avian canonical circuitry is similar to its mammalian counterpart and might constitute the structural basis of neuronal computation.

Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing

Abstract: This work describes a novel mechanism of laminar flow control of straight and backward swept wings with a comb-like leading edge device. It is inspired by the leading-edge comb on owl feathers and the special design of its barbs, resembling a cascade of complex 3D-curved thin finlets. The details of the geometry of the barbs from an owl feather were used to design a generic model of the comb for experimental and numerical flow studies with the comb attached to the leading edge of a flat plate. Due to the owls demonstrating a backward sweep of the wing during gliding and flapping from live recordings, our examinations have also been carried out at differing sweep angles. The results demonstrate a flow turning effect in the boundary layer inboards, which extends downstream in the chordwise direction over distances of multiples of the barb lengths. The inboard flow-turning effect described here, counter-acts the outboard directed cross-span flow typically appearing for backward swept wings. This flow turning behavior is also shown on SD7003 airfoil using precursory LES investigations. From recent theoretical studies on a swept wing, such a way of turning the flow in the boundary layer is known to attenuate crossflow instabilities and delay transition. A comparison of the comb-induced cross-span velocity profiles with those proven to delay laminar to turbulent transition in theory shows excellent agreement, which supports the laminar flow control hypothesis. Thus, the observed effect is expected to delay transition in owl flight, contributing to a more silent flight.

Embryonic development of the Little Owl (Athene noctua) and Tengmalm’s Owl (Aegolius funereus) compared to the American Barn Owl (Tyto furcata): reference data for staging

Abstract: Embryonic development is a fascinating subject for scientists from different biological disciplines, since it is determined by genetics, is linked to evolution, and involves morphological changes over a relatively short time period. Staging tables have been established to facilitate comparison between different clades of birds. However, embryological data for endangered and protected non-model birds are rare. Here we provide reference data for the embryonic development of the Little Owl (Athene noctua) and Tengmalm’s Owl (Aegolius funereus). We found differences in the development of these species compared with that of the American Barn Owl (Tyto furcata) with respect to the cere, beak and claws. Little Owls hatch at the most advanced state amongst these species with respect to plumage, size and weight; they incubate their eggs for just a week and can breed under more adverse conditions than the other two species.

Sound localization in barn owls studied with manipulated head-related transfer functions: beyond broadband interaural time and level differences.

Abstract: Interaural time and level differences are important cues for sound localization. We wondered whether the broadband information contained in these two cues could fully explain the behavior of barn owls and responses of midbrain neurons in these birds. To tackle this problem, we developed a novel approach based on head-related transfer functions. These filters contain the complete information present at the eardrum. We selected positions in space characterized by equal broadband interaural time and level differences. Stimulation from such positions provides reduced information to the owl. We show that barn owls are able to discriminate between such positions. In many cases, but not all, the owls may have used spectral components of interaural level differences that exceeded the known behavioral resolution and variability for discrimination. Alternatively, the birds may have used template matching. Likewise, neurons in the optic tectum of the barn owl, a nucleus involved in sensorimotor integration, contained more information than is available in the broadband interaural time and level differences. Thus, these data show that more information is available and used by barn owls for sound localization than carried by broadband interaural time and level differences.

Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing

Abstract: This work describes a novel mechanism of laminar flow control of a backward swept wing with a comb-like leading edge device. It is inspired by the leading-edge comb on owl feathers and the special design of its barbs, resembling a cascade of complex 3D-curved thin finlets. The details of the geometry of the barbs from an owl feather were used to design a generic model of the comb for experimental and numerical flow studies with the comb attached to the leading edge of a flat plate. Examination was carried out at different sweep angles, because life animal clearly show the backward sweep of the wing during gliding and flapping. The results demonstrate a flow turning effect in the boundary layer inboards, which extends along the chord over distances of multiples of the barb lengths. The inboard flow-turning effect described here, thus, counter-acts the outboard directed cross-span flow typically appearing for backward swept wings. From recent theoretical studies on a swept wing, such a way of turning the flow in the boundary layer is known to attenuate crossflow instabilities and delay transition. A comparison of the comb-induced cross-span velocity profiles with those proven to delay transition in theory shows excellent agreement, which supports the laminar flow control hypothesis. Thus, the observed effect is expected to delay transition in owl flight, contributing to a more silent flight