Common Kingfisher (Alcedo atthis)
The common kingfisher (Alcedo atthis) also known as Eurasian kingfisher, or river kingfisher, is a small kingfisher. It feeds mainly on fish, caught by diving, and has special visual adaptions to enable it to see prey under water. This sparrow-sized bird has the typical short-tailed, large-headed kingfisher profile; it has blue upperparts, orange underparts and a long bill.
The adult male has black bill with some red at the base. The legs and feet are bright red.
The female is identical in appearance to the male except that her lower mandible is orange-red with a black tip. The juvenile is similar to the adult, but with duller and greener upperparts and paler underparts. Its bill is black, and the legs are also initially black.
Habitat and distribution
Common kingfishers are important members of ecosystems and good indicators of freshwater community health.
The highest densities of breeding birds are found in habitats with clear water, which permits optimal prey visibility, and trees or
shrubs on the banks.
These habitats have also the highest quality of water, so the presence of this bird confirms the standard of the water.
Like all kingfishers, the common kingfishers is highly territorial; since it must eat around 60% of its body weight each day,
it is essential to have control of a suitable stretch of river. It is solitary for most of the year, roosting alone in heavy cover.
If another kingfisher enters its territory, both birds display from perches, and fights may occur, where a bird will grab the other’s
beak and try to hold it under water.
The courtship is initiated by the male chasing the female while calling continually, and later by ritual feeding, copulation usually following.
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 (10 in) below the surface. The wings are opened under water and the open eyes are protected by the transparent third eyelid. The bird rises beak-first from the
surface and flies back to its perch. At the perch the fish is adjusted until it is held near its tail and beaten against the perch several times.
Once dead, the fish is positioned lengthways and swallowed head-first. A few times each day, a small greyish pellet of fish bones and other indigestible remains is regurgitated.
The food is mainly fish up to 12.5 cm (4.9 in) long, but the average size is 2.3 cm (0.91 in). Minnows, sticklebacks, small roach and trout are typical prey.
About 60% of food items are fish, but this kingfisher also catches aquatic insects such as dragonfly larvae and water beetles, and, in winter, crustaceans including freshwater shrimps.
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 presence of a Common Kingfisher confirms the standard of the water.