A large number of rods and very few cones.
Explanation
The vertebrate eye functions as an optical instrument where the retina acts as the screen for image formation. The retina contains two primary types of photoreceptor cells: rods and cones, which react differently to light intensity and color.
Detailed Analysis:
- Rods: These cells are highly sensitive to light intensity and are essential for vision in low-light or dim conditions (scotopic vision). They do not detect color.
- Cones: These cells function best in bright light (photopic vision) and are responsible for color perception and high visual acuity.
- Adaptation in Nocturnal Birds: To see effectively in the dark, nocturnal birds like owls require maximum light sensitivity. Therefore, their retinas contain a large number of rods to capture the minimal available light. They possess very few cones, which is why they have poor color vision.
- Pupil Size: Contrary to A permanently contracted pupil during the day., the pupil of a nocturnal bird is large and dilates significantly in the dark to allow the maximum amount of light to enter the eye. A contracted pupil is a response to bright light.
Key Takeaway:
Rods are responsible for night vision and light sensitivity, whereas Cones are responsible for day vision and color differentiation.