Amazing Facts: The Common Kingfisher
The Common Kingfisher hunts from a perch 1–2 m (3–6 ft) above the water, on a branch, post or riverbank, bill pointing down as it searches for prey. It bobs its head when food is detected to gauge the distance, and plunges steeply down to seize its prey usually no deeper than 25 cm (19 in) below the surface. The wings are opened under water and the open eyes are protected by the transparent third eyelid. A challenge for any diving bird is the change in refraction between air and water. The eyes of many birds have two foveae (the fovea is the area of the retina the greatest density of light receptors), and a kingfisher is able to switch from the main central fovea to the auxiliary fovea when it enters water; a retinal streak of high receptor density which connects the two foveae allows the image to swing temporally as the bird drops onto the prey.
The egg-shaped lens of the eye points towards the auxiliary fovea, enabling the bird to maintain visual acuity underwater. Because of the positions of the foveae, the kingfisher has monocular vision in air, and binocular vision in water. The underwater vision is not as a sharp as in air, but the ability to judge the distance of moving prey is more important than the sharpness of the image. Each cone cell of a bird’s retina contains an oil droplet which may contain carotenoid pigments. These droplets enhance colour vision and reduce glare. Aquatic kingfishers have high numbers of red pigments in their oil droplets; the reason red droplets predominate is not understood, but the droplets may help with the glare or the dispersion of light from particulate matter in the water. The common Kingfisher must eat around 60% of its body weight each day.
The common kingfisher Pu la Deshpande Garden Pune