Pecten oculi of kestrel (Falco tinnunculus rupicolaeformes) and little owl (Athene noctua glaux): Scanning electron microscopy and histology with unique insights into SEM-EDX elemental analysis.

There is scanty data about the comparative morphological features between the pecten oculi of two carnivorous birds with different visual active clock hours: the diurnal common kestrel and the nocturnal little owl. This study illustrated the comparative gross, scanning electron microscopy, and histological characteristics between pecten oculi of kestrel and little owl. This study first attempts to describe the scanning electron microscopy-energy dispersive x-ray (SEM-EDX) elemental analysis at the parts (apex, middle, and base) of the pecten oculi of these two birds. The present study results observed the same position, origin, directions, parts, convoluted outer pleat surfaces, and SEM-EDX elemental analysis, but there were some minor variations due to the different visual active clock hours. These minor variations were summarized in the following points: pleat number (21-23 in the kestrel and 10-11 in the owl), shape (fan rhomboid in the kestrel and accordion in the owl), inter-pleat spaces (wider in the kestrel than in the owl), pigmentations (highly black pigmented in the owl than in the kestrel), hyalocyte cell aggregations (highest in the middle and dwindling at the apex and base in the kestrel, while highest in the middle and base and dwindling at the apex in the owl), and SEM-EDX elemental analysis percentage. SEM/EDX elemental analysis confirmed the presence of oxygen (the highest one), carbon, nitrogen (the second one), nitrogen (the third one), and aluminum (the lowest one) in varying percentages within the pecten oculi; these findings contribute to our understanding of its structural, adaptations with different visual active clock hours, and functional characteristics. RESEARCH HIGHLIGHTS: This study compared the pecten oculi of two carnivorous birds with different visual active clock hours: the diurnal common kestrel and the nocturnal little owl. Anatomically, the characteristic features were similar in both the birds, but some minor variations were observed adapted to their visual active clock hours. The pecten oculi of both birds were analyzed using SEM-EDX for elemental analysis, and it revealed that oxygen was the highest elemental concentration, followed by carbon and nitrogen. Aluminum concentrations were small as per SEM-EDX analysis. The study suggested that the pecten oculi of these birds are related to their active visual clocks and adaptive nutritional mechanisms.