Background: The anatomical information about the structure of the choana is lacking in literature, and its role in the olfactory and feeding mechanism is still unknown Results: The present study discusses the adaptation of choana to cranial kinesis during feeding process in different bird species: kestrel, common moorhen, and hoopoe. Kestrel possesses a kinetic skull while the hoopoe and common moorhen have kinetic one; however, the common moorhen skull seems highly kinetic more than that of the hoopoe that properly effect on the choanal epithelium. The choana of kestrel and hoopoe are lined by pseudostratified ciliated columnar epithelium, while choana of common moorhen have transitional epithelium beside pseudostratified ciliated columnar epithelium. The choana epithelium of each bird species provides with simple alveolar glands and numerous goblet cells. In kestrel and hoopoe, the secretion products of choanal glands contain neutral and sulfated mucin, while in the common moorhen, these glands secret neutral and carboxylate mucopolysaccharides. Conclusion: The choana of the three studied bird species apparents adaptation to the olfaction process but also affects the movement of skeletal elements of the skull during the feeding process

The dorsal epithelium of the free portion of tongue of laughing dove, Streptopelia senegalensis (granivorous) is characterized by presence of well-developed keratinized epithelium with desquamate parakeratinized one which is covering the anterior part of the free portion. Highly keratinized and stratified epithelium is covering the ventral surface of the anterior third of the free portion of the tongue and forming the lingual nail. Laryngeal area is covered dorsally by non-keratinized squamous epithelium. Frenulum is covered by a transitional-like epithelium. Both the dorsal and ventral surfaces of the free portion of the tongue of the common hoopoe, Upupa epops (insectivorous) are covered by thin non-keratinized squamous epithelium except that covered the areas of lingual tubercles, lingual wings and lingual papillae, which are covered by epithelium furnished dorsally by detached keratin. The laryngeal area is covered by non-keratinized squamous epithelium. The frenulum is covered by non-keratinized stratified squamous epithelium. It has been summarized that the differences in the structures of the avian tongue reflecting the differences in the feeding habits. The epithelium covering the tongue of the laughing dove is constructed for high mobility (up-down movement) in comparison with the epithelium of the common hoopoe that depends on its first action of feeding on the movement of the jaws and beak.

The digestive tract of the little owl, Athene noctua (Strigiformes: Strigidae), is described in two different seasons. The digestive tract of this bird follows the basic model for that of a predatory bird. The cervical esophagus is not expanded to form a crop. The internal surface of the esophagus forms numerous longitudinal folds provided with numerous mucous glands. These longitudinal folds increase in number and vary in depth posteriorly. The folds of the proventriculus are composed of simple branched tubular glands. The ventriculus is lined by a thin layer of koilin. The number of goblet cells gradually increases from the duodenum to the rectum, and the lymphatic tissue diffuses within the lamina propria. The esophageal glands secrete acid mucopolysaccharides, while the gastric glands of the stomach, the goblet cells, and crypts of Lieberkühn secrete acid mucopolysaccharides. Proteins were observed in the different histological structures of the digestive tract. Morphometric and histometric studies showed differences between summer and winter in the esophagus and glandular stomach (especially in winter), but no seasonal differences were seen in the muscular stomach, or small and large intestines.

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This study gives a comprehensive description of eyelids movement in little owl and discusses the impact of some surrounding conditions in their kinetic performance. The present study used the video's recording technique to record the kinetic activity of eyelids, besides the anatomical and histological studies of the eyelid's structure. The fundamental eyelid movements can be uniquely and reliably characterized by their anatomical relationship that was confirmed via video recording for their kinetic activity. The levator palpebrae muscle is considered a main generating motor for the upper eyelid; in the little owl, this muscle splits into multiple directions and is distinguished from the levator palpebrae superioris (Lps) and the levator anguli oculi (Lao) muscle. That anatomical pattern of insertion increases the movement of the upper lid. On the other side, the contraction of depressor palpebrae inferioris (Dpi) muscle and the active upward forces of levator palpebrae muscle help in increasing the opening of the eye's fissure. However, the closure process is produced from the passive downward forces and relaxation of the levator palpebrae superioris (Lps), levator anguli oculi (Lao), and depressor palpebrae inferioris muscle, as well as the contraction of retractor anguli oculi lateralis (Raol) and medialis (Raom) muscle. The present results also recorded that nictitating membrane's (Nm) movement is reversely proportionate to the level of kinetic of other eyelids. The mobility of Nm in little owl occurs under the effect of artificial external stress. These anatomical data and sequence video recordings have confirmed that the upper eyelid moves more compared to other eyelids. The authors also suggest that the mobility of eyelids may get stimulated through external pressure force of some surrounding structure like the periorbital sheet. Also, the histological study exhibited that the structure of two eyelids is very similar in the little owl and the variability is showing in the number of cell layers that forms their epithelium of skin and palpebral surfaces, the distribution of pigment granules, and degree of keratinization on their surface. That variability in the histological characters of eyelids may counteract the abrasive forces occurring during the opening and closing processes.

This study used both anatomical and histological techniques to investigate the orbital gland's topographic relationship with the surrounding system, using the hoopoe and cattle egret as biological models. Hoopoe has a spindle‐shaped lacrimal gland that is suspended on the lateral edge of the frontal bone, whereas cattle egret has a tiny lacrimal gland that is embedded posteriorly within the periorbital fascia. The hoopoe's lacrimal gland has a single duct that runs parallel to the nasolacrimal duct and opens into the posterior nostril hole. In the cattle egret, the tubule‐alveolar secretory components comprise neutral and acid glycosaminoglycan. In addition, the Harderian gland is found in both these species, but their draining ducts differ; the Harderian gland of the hoopoe opens into the anterodorsal to the conjunctival fornix, whereas the Harderian gland of the egret opens anteriorly. In both hoopoe and egret, the secretions of Harderian gland include neutral and acid glycosaminoglycan. The Harderian gland is categorized as type II in hoopoe and type I in cattle egrets. The present results concluded that both orbital glands of two bird species studied play an essential role in eye health, where cleaning and lubrication of the cornea surface. Furthermore, the lacrimal gland's location and secretory features may strengthen the olfactory sensitivity of hoopoe, which relies heavily on scent to locate their food, whereas egret relies heavily on visual cues.

This study gives a comprehensive description of eyelids movement in little owl and discusses the impact of some surrounding conditions in kinetic performance of these eyelids. The present study used the video's recording technique to record the kinetic activity of lids, beside the anatomical, and the histological studies of the eyelids structure. The present authors found that the fundemental eyelids movements can be uniquely and reliably characterized by their anatomical relationships that confirmed also via video record of kinetic performance of these eyelids. The results show that levator palpebrae muscle split into many directions as a main generate motor to increasing the movement of the upper lid. In other side, the contraction of Depressor palpebral inferioris muscle together with the active upward forces of levator palpebrae muscle resultin g in opening the eye. While, the closure of lids arise from the passive downward forces and relaxation of the levator palpebrae and Depressor palpebral inferioris muscle as well as, the cooperation action of retractor anguli oculi lateralis and medialis muscle. The results also recorded that NM movement is reversely proportion to the level of kinetic of other eyelids. . The mobility of Nm in little owl occurs under effect artificially external stress. These anatomical data and sequence video records have confirmed that the upper eyelid move more compare to other lids. The present authors also suggest that the mobility of lids may stimulate through external pressure force of some surrounding structure like periorbital sheet. Also, the histological study exhibited that the structure of two eyelids is very similar in the little owl and the variability are showing in the number of cell layers that forms their epithelium of skin and palpebral surfaces, the distribution of pigment granules within them, as well as, the degree of keratinization on their surface.