Comparative histology of the trachea and lung in migratory and predatory birds: the white stork (Ciconia ciconia), long-legged buzzard (Buteo rufinus), and common kestrel (Falco tinnunculus)

Abstract

This study comparatively examined the histological and histochemical features of the respiratory systems (trachea and lungs) of the white stork ( Ciconia ciconia ), long-legged buzzard ( Buteo rufinus ), and common kestrel ( Falco tinnunculus ), which have different ecological niches and flight characteristics. In this study, trachea and lung tissues from three birds of each species were used. After fixation in 10% formaldehyde, the tissues were subjected to routine histological procedures, embedded with paraffin, and 5 μm sections were obtained. Crossmon's triple staining technique was used to determine the general histological structure, and PAS with light green and AB/PAS (pH: 1 and pH: 2.5) staining were applied for the detection of mucopolysaccharides. In all three species examined, it was determined that the trachea has a tunica mucosa composed of pseudostratified columnar ciliated epithelium and goblet cells, and that the hyaline cartilage rings are "C" shaped. Intraepithelial mucous glands were observed to be more dense and prominent in active predators such as buzzards and kestrels compared to storks. Lung histology revealed the presence of intrapulmonary primary bronchi, secondary bronchi, parabronchi, atria, and air capillaries. Type I and Type II pneumocytes have been distinguished in the air capillaries where gas exchange takes place. Histochemical analyses showed that tracheal glands secrete both acidic and neutral mucopolysaccharides. The findings of the present study suggest that differences in the respiratory system morphology among the examined species may be associated with ecological adaptations, including flight behavior, respiratory rate, and exposure to environmental irritants. The relatively lower number of intraepithelial mucus glands observed particularly in the trachea of ​​storks may reflect species-specific respiratory adaptations and could be associated with relatively lower respiratory rates and different non-vocal communication behaviors (*bill clattering*). However, further functional and comparative studies are needed to clarify these potential relationships.