Investigation of Glandula Uropygialis in Different Avian Species Using Morphometric and Histological Methods.

The aim of this study was to identify the glandula uropygialis's macroanatomical and histological structure in male and female birds (stork, goose, eagle, pigeon, crow and sparrowhawk) that belong to different populations. A total of 58 specimens were used in the study. The study materials were delivered to our laboratory by nature conservation and national parks, and no animals were euthanised for this study. The longitudinal and transversal lengths, dorsoventral heights and feather length of the glandula uropygialis and papilla uropygialis were measured with a digital calliper. Haematoxylin-eosin and Masson trichrome staining were performed for histological examinations. The shape of the glandula uropygialis was found to be pear-shaped in pigeons and sparrowhawks, heart-shaped in geese, kidney-shaped in eagles and oval-fascule-shaped in storks. In the crow, the shape of the glandula uropygialis was different from the other species in that it was located dorso-caudally. Histomorphological examination of the glands of these species revealed that the gland generally consisted of two lobes, right and left, surrounded by connective tissue from the outside. The parenchyma of these lobes consisted of tubulo-alveolar secretory glands with a radial arrangement from the periphery to the centre. The glands within the lobes differed from the periphery to the centre and although the general histomorphological appearance was similar between bird species, some differences were observed between species. Similar stromal structure was observed in all bird species evaluated in the study. However, the reticular connective tissue forming the roof of the gland was found to be more developed in pigeons, especially in Masson's trichroma staining. The degenerative layer in the glands was more prominent in the eagle, followed by the goose and crow. Although a common general histological structure was observed among bird species, simple histomorphological differences were found between these formations, but no differences were found between the sexes. The results obtained will be compared with the findings of the aves class and will provide a data source for this special gland specific to birds. It is thought that the results obtained may help to determine the functional properties of the gland and contribute to the science of ornithology.

Geometric morphometric analysis of beak shape of Columbimorphae (Columbas, Van, Mardin and Dönek).

Selective breeding over centuries has led to the emergence of numerous pigeon breeds from the single species Columba livia, showcasing unparalleled phenotypic diversity. In Eastern Turkey, Van pigeons originate, while Tumbler pigeon varieties thrive countrywide, reflecting local traditions. The avian beak, vital for survival, offers insights into domestication and traits influenced by natural selection. Geometric morphometrics, a shape analysis method, allows for a comprehensive examination of beak shapes among domestic pigeons, providing a nuanced understanding of their complexity. Understanding beak diversity in pigeons, especially those found in Turkey, enhances our knowledge of avian evolution and adaptation processes. The study utilized 48 skulls from 4 pigeon breeds, including wild rock pigeons and domestic pigeons of Tumbler, Mardin and Van breeds, all free from pathological lesions and adults. Geometric morphometric analyses of beak shape were conducted using dorsal and lateral photographs, with landmarks placed using tpsDig software. MorphoJ software facilitated procrustes analysis and principal component analysis (PCA) to assess morphological variability and differentiate pigeon breeds based on shape patterns, with significance set at p < 0.05. PCA revealed significant shape variations among pigeon breeds, with 47 principal components identified for lateral beak views and 36 principal components for dorsal views. Canonical variates analysis further distinguished morphological patterns among breeds, indicating distinct shape variations in both dorsal and lateral views, elucidating the unique characteristics of each breed's beak morphology. Our results demonstrate statistically significant differences in pigeon beak shape, particularly in the lateral view, confirming the importance of these variations (p < 0.05) and suggesting that such differences occur less than 5% of the time under the null hypothesis.

Comparative study of the ciliary body and iris morphology in the anterior eye chamber of five different vertebrate classes.

One crucial component of the optical system is the ciliary body (CB). This body secretes the aqueous humour, which is essential to maintain the internal eye pressure as well as the clearness of the lens and cornea. The histological study was designed to provide the morphological differences of CB and iris in the anterior eye chambers of the following vertebrate classes: fish (grass carp), amphibians (Arabian toad), reptiles (semiaquatic turtle, fan-footed gecko, ocellated skink, Egyptian spiny-tailed lizard, Arabian horned viper), birds (common pigeon, common quail, common kestrel), and mammals (BALB/c mouse, rabbit, golden hamster, desert hedgehog, lesser Egyptian jerboa, Egyptian fruit bat). The results showed distinct morphological appearances of the CB and iris in each species, ranging from fish to mammals. The present comparative study concluded that the morphological structure of the CB and iris is the adaptation of species to either their lifestyle or survival in specific habitats.

Influence of behavioural and morphological group composition on pigeon flocking dynamics.

Animals rely on movement to explore and exploit resources in their environment. While movement can provide energetic benefits, it also comes with energetic costs. This study examines how group phenotypic composition influences individual speed and energy expenditure during group travel in homing pigeons. We manipulated the composition of pigeon groups based on body mass and leadership rank. Our findings indicate that groups of 'leader' phenotypes show faster speeds and greater cohesion than 'follower' phenotype groups. Additionally, we show that groups of homogenous mass composition, whether all heavy or all light, were faster and expended less energy over the course of a whole flight than flocks composed of a mixture of heavy and light individuals. We highlight the importance of considering individual-level variation in social-level studies, and the interaction between individual and group-level traits in governing speed and the costs of travel.

Radial porosity profiles are a powerful tool for tracing locomotor maturation in developing limb bones.

Radial porosity profiles (RPP) are a new quantitative osteohistological parameter designed to capture the dynamic changes in the primary porosity of limb bones through ontogeny, providing insights into skeletal growth and functional development of extant and extinct vertebrates. Previous work hypothesized that RPP channelization-the intraskeletal alignment of RPPs across different bones resulting from similar cortical compaction patterns-indicates increasing locomotor performance of the developing limbs. By investigating RPPs in ontogenetic series of pheasants, pigeons and ducks representing distinct locomotor developmental strategies, we test this hypothesis here and show that RPPs are indeed powerful osteohistological correlates of locomotor ontogeny. Qualitative and quantitative analyses reveal strong association between RPP channelization and fledging, the most drastic locomotor transition in the life history of volant birds. The channelization signal is less clear in precocial leg function; however, when additional intraskeletal and intercohort RPP characteristics are considered, patterns related to leg precocity can also be identified. Thus, we demonstrate that RPPs can be used in future by palaeobiologists to generate breakthroughs in the study of the ontogeny and evolution of flight in fossil birds and pterosaurs. With further baseline data collection from modern terrestrial vertebrates, RPPs could also test hypotheses regarding ontogenetic postural shifts in dinosaurs and other terrestrial archosaurs.

Low parasite infestations in high densities: The paradox of woodpigeons in urban areas.

The type of habitat occupied by avian populations has a marked effect on the parasitises they host. The growth of cities and urban areas in recent decades has favoured some species of birds adapted to these types of habitats - urban exploiters - although the effects of urbanisation on the parasitism of wildlife are not always well known. This study compares the ectoparasites characteristic of two differentiated populations of woodpigeons, one located in a predominantly urban environment and the other in a rural one. Most of the species found were chewing lice, with Columbicola claviformis and Campanulotes bidentatus being dominant. Despite the higher density of the urban population, woodpigeon individuals were characterised by a lower abundance of chewing lice, as well as the presence of ectoparasites typical of feral pigeons such as Hohorstiella lata and the hippoboscids fly, Pseudolynchia canariensis. Similarly, birds with lower weights showed a higher parasitic load, which became more noticeable in urban woodpigeons. The lower ectoparasite load of urban hosts represents a health advantage compared with rural populations, which could be one of the causes of greater growth and reproductive success in urban populations of woodpigeons.

Revision of some mensural measurements, food preference, and haematological parameters in breeding pairs of blue rock pigeon, Columba livia sampled from Punjab Pakistan / Revisão de algumas medidas mensurais, preferência alimentar e parâmetros hematológicos em pares de criação de pombo blue rock (Columba livia), amostragem de Punjab, Paquistão

The present study describes the haematological profile, feeding preference, and comparison of morphometric characters of blue rock pigeon (Columba livia) breeding pairs. For this purpose, 25 pairs (25 samples per sex) were sampled through Mist nets from district Okara and Bahawalnagar, Punjab, Pakistan. Birds were then anaesthetized with a combination of ketamine HCL (10 mg/kg) and diazepam (0.2 mg/kg) and subjected to morphometric measurements. 5µL blood also was taken from the jugular vein of each anaesthetized bird for haematological analysis. Few pairs were also dissected to remove gastrointestinal tracts (GITs) for food preferences. Results revealed that there are no significant differences in the haematological parameters and feeding preference of breeding pairs of Columba livia. The gut analysis further revealed, the major portion of gut contents consisted of pea and corn in most of the pairs. Regarding the mensural measurements, significant differences were recorded in the body weight, length of the longest primary feather, and chest circumference, whereas the rest of the studied parameters remain nonsignificant between sexes. So, it is concluded that apart from 3 morphometric parameters (body weight, length of longest primary feather and chest circumference), both sexes are alike in term of morphometry, haematology and food preference.

O presente estudo descreve o perfil hematológico, a preferência alimentar e a comparação de caracteres morfométricos de casais reprodutores de pombo-rocha (Columba livia). Para tanto, 25 pares (25 amostras por sexo) foram amostrados por meio de redes de névoa do distrito de Okara e Bahawalnagar, Punjab, Paquistão. As aves foram então anestesiadas com uma combinação de cetamina HCL (10 mg/kg) e diazepam (0,2 mg/kg) e submetidas a medidas morfométricas; 5 µL de sangue também foram retirados da veia jugular de cada ave anestesiada para análise hematológica. Poucos pares também foram dissecados para remover o trato gastrointestinal (GITs) para preferências alimentares. Os resultados revelaram que não há diferenças significativas nos parâmetros hematológicos e na preferência alimentar dos casais reprodutores de Columba livia. A análise intestinal revelou ainda que a maior parte do conteúdo intestinal consistia em ervilha e milho na maioria dos pares. Em relação às medidas mensurais, foram registradas diferenças significativas no peso corporal, comprimento da pena primária mais longa e circunferência torácica, enquanto os demais parâmetros estudados permanecem não significativos entre os sexos. Assim, conclui-se que além de três parâmetros morfométricos (peso corporal, comprimento da pena primária mais longa e circunferência torácica), ambos os sexos são semelhantes em termos de morfometria, hematologia e preferência alimentar.

Pretecto- and ponto-cerebellar pathways to the pigeon oculomotor cerebellum follow a zonal organization.

Both birds and mammals have relatively large forebrains and cerebella. In mammals, there are extensive sensory-motor projections to the cerebellum through the pontine nuclei originating from several parts of the cerebral cortex. Similar forebrain-to-cerebellum pathways exist in birds, but the organization of this circuitry has not been studied extensively. Birds have two nuclei at the base of the brainstem that are thought to be homologous to the pontine nuclei of mammals, the medial and lateral pontine nuclei (PM, PL). Additionally, birds are unique in that they have a pretectal nucleus called the medial spiriform nucleus (SpM) that, like the pontine nuclei, also receives projections from the forebrain and projects to the oculomotor cerebellum (OCb; folia VI to VIII). The OCb also receives input from the pretectal nucleus lentiformis mesencephali (LM), which analyzes visual optic flow information resulting from self-movement. In this study, we used single or double injections of fluorescent tracers to study the organization of these inputs from PM, PL, SpM and LM to the OCb in pigeons. We found that these inputs follow a zonal organization. The most medial zone in the OCb, zone A1, receives bilateral inputs from the lateral SpM, PL and LM. Zones A2 and C receive a bilateral projection from the medial SpM, and a mostly contralateral projection from PM and LM. We discuss how the pathway to zone A1 processes mainly visuo-motor information to spinal premotor areas, whereas the pathways to zone A2/C processes somato-motor and visuo-motor information and may have a feedback/modulatory role.

Change in the neurochemical signature and morphological development of the parvocellular isthmic projection to the avian tectum.

Neurons can change their classical neurotransmitters during ontogeny, sometimes going through stages of dual release. Here, we explored the development of the neurotransmitter identity of neurons of the avian nucleus isthmi parvocellularis (Ipc), whose axon terminals are retinotopically arranged in the optic tectum (TeO) and exert a focal gating effect upon the ascending transmission of retinal inputs. Although cholinergic and glutamatergic markers are both found in Ipc neurons and terminals of adult pigeons and chicks, the mRNA expression of the vesicular acetylcholine transporter, VAChT, is weak or absent. To explore how the Ipc neurotransmitter identity is established during ontogeny, we analyzed the expression of mRNAs coding for cholinergic (ChAT, VAChT, and CHT) and glutamatergic (VGluT2 and VGluT3) markers in chick embryos at different developmental stages. We found that between E12 and E18, Ipc neurons expressed all cholinergic mRNAs and also VGluT2 mRNA; however, from E16 through posthatch stages, VAChT mRNA expression was specifically diminished. Our ex vivo deposits of tracer crystals and intracellular filling experiments revealed that Ipc axons exhibit a mature paintbrush morphology late in development, experiencing marked morphological transformations during the period of presumptive dual vesicular transmitter release. Additionally, although ChAT protein immunoassays increasingly label the growing Ipc axon, this labeling was consistently restricted to sparse portions of the terminal branches. Combined, these results suggest that the synthesis of glutamate and acetylcholine, and their vesicular release, is complexly linked to the developmental processes of branching, growing and remodeling of these unique axons.

Assessment of the pigeon (Columba livia) retina with spectral domain optical coherence tomography.

BACKGROUND: To assess the normal retina of the pigeon eye using spectral domain optical coherence tomography (SD-OCT) and establish a normative reference. METHODS: Twelve eyes of six ophthalmologically normal pigeons (Columba livia) were included. SD-OCT images were taken with dilated pupils under sedation. Four meridians, including the fovea, optic disc, red field, and yellow field, were obtained in each eye. The layers, including full thickness (FT), ganglion cell complex (GCC), thickness from the retinal pigmented epithelium to the outer nuclear layer (RPE-ONL), and from the retinal pigmented epithelium to the inner nuclear layer (RPE-INL), were manually measured. RESULTS: The average FT values were significantly different among the four meridians (p < 0.05), with the optic disc meridian being the thickest (294.0 ± 13.9 µm). The average GCC was thickest in the optic disc (105.3 ± 27.1 µm) and thinnest in the fovea meridian (42.8 ± 15.3 µm). The average RPE-INL of the fovea meridian (165.5 ± 18.3 µm) was significantly thicker than that of the other meridians (p < 0.05). The average RPE-ONL of the fovea, optic disc, yellow field, and red field were 91.2 ± 5.2 µm, 87.7 ± 5.3 µm, 87.6 ± 6.5 µm, and 91.4 ± 3.9 µm, respectively. RPE-INL and RPE-ONL thickness of the red field meridian did not change significantly with measurement location (p > 0.05). CONCLUSIONS: Measured data could be used as normative references for diagnosing pigeon retinopathies and further research on avian fundus structure.

Vision adaptation in the laughing dove (Streptopelia senegalensis, Linnaeus, 1766) inferred from structural, ultrastructural, and genetic characterization.

Neuroanatomy of the retina reflects adaptation and acclimation for dark and light conditions. Retinal cells and genes must be functionally adjusted to various environmental luminosities. Opsins are brilliant molecules to assess the adaptations at the genetic and phenotypic levels. Photic adaptations may reveal new mechanisms that enhance vision abilities. Through the investigation of histological, ultrastructural constituents of the whole retinal layers, and the sequencing of shortwave length sensitive opsin 1 (SWS1) of the laughing dove (Streptopelia senegalensis), the current study confirms the plasticity of the retina in response to the natural photic conditions. Retinal pigmented epithelium has plentiful melanosomes, signifying a highly adapted eye for maximum light perception and protection. Variously colored oil droplets signify high color vision ability. Stratified outer nuclear layer with many Müller cells suggests high sensitivity to dim conditions and high retinal regeneration. The penetration of outer limiting membrane by photoreceptor nuclei and Müller cell microvilli could minimize the light reflection. Oligodendrocytes establish thick myelination demanded for a keen visual acuity. A functional violet sensitive SWS1 with crucial Ser90 is presumed. Molecular phylogeny showed a secondary loss as color vision was shifted back from ultraviolet (UV) sensitivity to the ancestral avian violet sensitivity, thus improving visual resolution. However, SWS1 has some UV sensitive residues. These findings implicate not only spectral adaptations with high color vision ability and acuity but also photoinduced structural reorganizations. Further studies are needed to assess the secrets between photons and the structural genes.

Soft biohybrid morphing wings with feathers underactuated by wrist and finger motion.

Since the Wright Flyer, engineers have strived to develop flying machines with morphing wings that can control flight as deftly as birds. Birds morph their wing planform parameters simultaneously-including sweep, span, and area-in a way that has proven to be particularly challenging to embody robotically. Previous solutions have primarily centered around the classical aerospace paradigm of controlling every degree of freedom to ensure predictable performance, but underperform compared with birds. To understand how birds accomplish wing morphing, we measured the kinematics of wing flexion and extension in common pigeons, Columba livia The skeletal and feather kinematics show that the 20 primary and 20 secondary feathers are coordinated via approximately linear transfer functions controlled by wrist and finger motion. To replicate this control principle in a robot, we developed a biohybrid morphing wing with real feathers to understand the underlying design principles. The outcome, PigeonBot, embodies 42 degrees of freedom that control the position of 40 elastically connected feathers via four servo-actuated wrist and finger joints. Our flight tests demonstrate that the soft feathered wings morph rapidly and robustly under aerodynamic loading. They not only enable wing morphing but also make robot interactions safer, the wing more robust to crashing, and the wing reparable via "preening." In flight tests, we found that both asymmetric wrist and finger motion can initiate turn maneuvers-evidence that birds may use their fingers to steer in flight.

A cortex-like canonical circuit in the avian forebrain.

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.

Effects of incubation and chick rearing on intestinal morphology, digestive enzyme activities, and mRNA expression of nutrient transporter genes in the pigeon (Columba livia) under artificial farming conditions.

The present study investigated the changes in morphology, enzyme activities in the pancreas and mucosa, and nutrient transporter gene expression in the duodenum and jejunum in male and female pigeons during the incubation and chick-rearing periods. Forty-two pairs of White King pigeons with 2 fertile eggs per pair were randomly divided into 7 groups by different breeding stages. The crypt depth of the duodenum and jejunum reached the peak at day 1 (R1) and day 7 (R7) of chick rearing, respectively. The jejunum surface area increased to a maximum value at R1. Amylase activity in the pancreas decreased to the lowest value at R1, whereas trypsin and lipase activities peaked at 17 D of incubation (I17) and R7, respectively. In male pigeons, mucosal Na+-K+-ATPase activity in the duodenum and jejunum was the highest at R15 and it was at I17 in female pigeons. Jejunum sucrose activity in female pigeons was higher at I4 than that at I17 (P < 0.05). The gene expression of FAT/CD36 and I-FABP in the duodenum gradually increased and then declined in the late chick-rearing period. SGLT1 in the jejunum decreased to a lower level at I17 and R25 in male pigeons (P < 0.05). GLUT2 expression in female duodenum and male jejunum decreased to a lower value at I17 compared with that at R15 (P < 0.05). In the late of incubation (from I10 to I17), expression of duodenum CAT1, B0AT1, and PepT1 and jejunum CAT1, ASCT1, and PepT1 in female pigeons was significantly reduced (P < 0.05), whereas opposite results were found in male jejunum CAT1 and duodenum ASCT1. In conclusion, variations of intestinal morphology, activities of pancreatic and mucosal enzymes, and gene expression of nutrient transporters during incubation and chick-rearing periods, underlying potential changes of digestive and absorptive function and intestinal adaptation with sexual effects, may represent a complicated response to stimuli of different breeding stages.

Comparative gross and scanning electron microscopical study of the oropharyngeal roof of young and adult domestic pigeons (Columba livia domestica).

The present study aims to compare the morphology of the oropharyngeal roof of young and adult domestic pigeon (Columba livia domestica) by gross observation, morphometric measurements, and scanning electron microscopy (SEM). The oropharyngeal roof was divided into the palate and pharyngeal roof. The palate was narrow triangular in shape and concave along its length. It could be divided into a rostral part contained three longitudinal palatine ridges and a caudal part contained the choanal slit. The choanal slit consisted of narrow rostral and wide caudal parts. The edges of the narrow part were encircled by small caudomedially directed papillae. On the contrary, the edges of the wide part of slit were free from papillae. By SEM, the palatal mucosa in young pigeon showed primordia of small papillae which increased in number and size forming a longitudinal row of papillae parallel to the edges of the rostral narrow part of slit in adult pigeon. The surface of the pharyngeal roof appeared smooth in young pigeon, while in adult pigeon, it showed dome-shaped elevations. The infundibular cleft had smooth edges. The caudal part of the pharyngeal roof formed an elevated transverse mucosal fold on which a transverse row of conical-shaped papillae was present. In conclusion, our results documented the presence of some differences between the oropharyngeal roof of young and adult pigeon, which suggest a high degree of functional adaptation in adult pigeon to their diet compared to young pigeon. Such adaptations might increase the efficiency of food prehension in adult pigeon. The present study compared the morphology of the oropharyngeal roof of young and adult domestic pigeon by gross observation, morphometry, and scanning electron microscopy. The morphometrical data showed higher values in adult pigeon compared to young pigeon. The palatal mucosa and the pharyngeal roof of adult pigeon showed papillae and elevations that were not present in young pigeon. Our results suggest a high degree of functional adaptation in adult pigeon to their diet compared to young pigeon. Such adaptations might increase the efficiency of food prehension in adult pigeon.

Comparative study of the distribution of NOS-positive neurons in pigeon intestine.

Nitric oxide (NO) plays an important role in regulating gut motility, mucosal barrier function and secretions in the enteric nervous system. Nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) staining has been used to identify nitrergic neurons of the enteric nervous system in different species. However, NADPH-d staining lacks specificity because it also reflects the presence of enzymes other than nitric oxide synthase (NOS). Therefore, NOS immunohistochemistry techniques are needed to test for nitrergic neurons in the avian gut. In the present work, the morphology, density and size of NOS-positive neurons in the duodenum, jejunum, ileum, caecum and rectum myenteric plexus of adult pigeons were investigated using NOS immunohistochemistry and whole-mount preparations techniques. The density of NOS-positive ganglion was highest in the ileum, similar to the caecum and rectum, and the lowest staining levels were observed in the duodenum. The staining intensity of NOS-positive neurons in the duodenum, jejunum and ileum was dark, followed by the rectal regions, with weak staining in the caecum. These results suggested that NOS immunohistochemistry and whole-mount preparation techniques provide an effective assessment method of the ganglia in the pigeon intestinal myenteric nerve plexus and are more accurate for cell counting compared with conventional sections.

Searching for magnetic compass mechanism in pigeon retinal photoreceptors.

Migratory birds can detect the direction of the Earth's magnetic field using the magnetic compass sense. However, the sensory basis of the magnetic compass still remains a puzzle. A large body of indirect evidence suggests that magnetic compass in birds is localized in the retina. To confirm this point, an evidence of visual signals modulation by magnetic field (MF) should be obtained. In a previous study we showed that MF inclination impacts the amplitude of ex vivo electroretinogram (ERG) recorded from isolated pigeon retina. Here we present the results of an analysis of putative MF effect on one component of ERG, the photoreceptor's response, isolated from the total ERG by adding sodium aspartate and barium chloride to the perfusion solution. Photoresponses were recorded from isolated retinae of domestic pigeons Columba livia. The retinal samples were placed in MF that was modulated by three pairs of orthogonal Helmholtz coils. Light stimuli (blue and red) were applied under two inclinations of MF, 0° and 90°. In all the experiments, preparations from two parts of retina were used, red field (with dominant red-sensitive cones) and yellow field (with relatively uniform distribution of cone color types). In contrast to the whole retinal ERG, we did not observe any effect of MF inclination on either amplitude or kinetics of pharmacologically isolated photoreceptor responses to blue or red half-saturating flashes. A possible explanations of these results could be that magnetic compass sense is localized in retinal cells other than photoreceptors, or that photoreceptors do participate in magnetoreception, but require some processing of compass information in other retinal layers, so that only whole retina signal can reflect the response to changing MF.

Comparative Morphological Features of Syrinx in Male Domestic Fowl Gallus gallus domesticus and Male Domestic Pigeon Columba livia domestica: A Histochemical, Ultrastructural, Scanning Electron Microscopic and Morphometrical Study.

Many studies have been carried out to investigate the morphological structure of the syrinx in many bird species. However, the cellular organization of the syrinx in the fowls and pigeons is still unclear. The current study revealed that in fowl and pigeon, the syrinx is formed of three main parts including tympanum (cranial) part, intermediate syringeal part, and bronchosyringeal (caudal) part, in addition to pessulus and tympaniform membranes. A great variation in the structural characteristics of syrinx of fowl and pigeon was recorded. In fowl, the tympaniform membranes showed a characteristic distribution of elastic and collagen fibers which increase the elasticity of tympaniform membranes. Moreover, the bony pessulus helps the medial tympaniform membranes to be stiffer, vibrate more strongly so that louder sound will be generated. In pigeon, the lateral tympaniform membrane is of greater thickness so that the oscillation of this membrane is reduced and the amplitude is lower. Moreover, the pessulus is smaller in size and is formed mainly of connective tissue core (devoid of cartilaginous or bony plates), resulting in the failure of stretching and vibrating of the medial tympaniform membranes, that leads to the generation of deeper sound. Electron microscopic examination of the syringes of fowls and pigeons revealed numerous immune cells including dendritic cells, plasma cells, mast cells, and lymphocytes distributed within syringeal mucosa and invading the syringeal epithelium. Telocytes were first recorded in the syrinx of fowls and pigeons in this study. They presented two long telopodes that made up frequent close contacts with other neighboring telocytes, immune cells, and blood capillaries.

Ultrastructural studies on the pancreatic acini in duck (Anas boscas) and pigeon (Columba livia).

The aim of this research work was to study the histological structure of the pancreatic acini by transmission electron microscope in two avian species, duck and pigeon. The specimens were collected and processed for electron microscopic study. The results showed that the acini of the two avian species were two types; the first one was an electron dense and the second one an electron lucent. The light acinar cells were larger in size than the dark cells. These cells contained centrally located ovoid nuclei with prominent nucleoli and abundant euchromatin. The cytoplasm was electron lucent, with many rough endoplasmic reticulum, polymorphic mitochondria. Numerous zymogen granules were distributed in the basal part and around the nucleus, so these cells considered active cells. The dark acinar cells were characterized by an electron dense cytoplasm. The most prominent cell organelle in these cells were the zymogen granules that appeared in different sizes while other organelles as mitochondria, and rough endoplasmic reticulum were inconspicuous or few, so these cells were considered as inactive cells. The nucleus with indented nuclear membrane located centrally with prominent nucleoli and abundant heterochromatin. Prominent intercellular spaces between the individual acinar cells, as well as well-developed basement membrane separating the electron dense cells and the lumen contained the secretion between acinar cells. It could be concluded that the acinar cells in ducks and pigeons were divided into two types, that is, light and dark acinar cells which mainly attributed to the activity of these cells.

How flight feathers stick together to form a continuous morphing wing.

Variable feather overlap enables birds to morph their wings, unlike aircraft. They accomplish this feat by means of elastic compliance of connective tissue, which passively redistributes the overlapping flight feathers when the skeleton moves to morph the wing planform. Distinctive microstructures form "directional Velcro," such that when adjacent feathers slide apart during extension, thousands of lobate cilia on the underlapping feathers lock probabilistically with hooked rami of overlapping feathers to prevent gaps. These structures unlock automatically during flexion. Using a feathered biohybrid aerial robot, we demonstrate how both passive mechanisms make morphing wings robust to turbulence. We found that the hooked microstructures fasten feathers across bird species except silent fliers, whose feathers also lack the associated Velcro-like noise. These findings could inspire innovative directional fasteners and morphing aircraft.