Birds
Kingfisher
Alcedinidae · also called kingfishers
The kingfisher everyone pictures is a flash of blue over a river, plunging headfirst after a fish. That bird is real, and its dive is precise enough that engineers copied its bill to quiet a bullet train. But most kingfishers never see a river — the family is mainly forest birds, and the biggest of them is the laughing kookaburra.
Overview
Kingfishers are the family Alcedinidae, around 115 species, on every continent except Antarctica and most diverse in the forests of Southeast Asia and Australasia. They are compact, large-headed, short-tailed birds with a long, straight, dagger-shaped bill. All are carnivores, but only a minority are the fish-diving birds of streams and coasts; the rest, including the kookaburras, hunt insects and small vertebrates on land.
The dive
A fishing kingfisher watches from a perch, judges a fish’s position while correcting for the way water bends light, then dives almost vertically, closing a protective eyelid as it hits the surface and grabbing the fish in its bill. The smooth wedge of its bill enters the water with almost no splash — a shape Japanese engineers copied for the nose of the Shinkansen bullet train to kill the boom it made leaving tunnels.
Colour and nests
The brilliant blues and greens are structural colours, made by feather nanostructure rather than pigment, so they shift with the angle and never fade. Most kingfishers nest in a tunnel, dug into a bank or a termite mound or in a tree hole.
Status
Kingfishers as a family are Not Evaluated. Widespread species like the common and belted kingfishers and the kookaburra are secure, but many Pacific island kingfishers have tiny ranges and are threatened by deforestation and introduced predators — several are Critically Endangered, and the Guam kingfisher has been extinct in the wild since the 1980s.
Kingfisher: common questions
Do all kingfishers catch fish?
No, and this is the biggest misconception about them. The name comes from the bright riverside birds of Europe and North America that dive for fish, but they are a minority of the family. Most of the roughly 115 kingfisher species are birds of forest, woodland, and even dry scrub that hunt insects, spiders, worms, lizards, frogs, snakes, and small mammals and birds by watching from a perch and pouncing onto the ground or foliage. The kookaburras are the best-known example, being large land-hunting kingfishers of Australian woodland. The fishing habit evolved within the family, and the ancestral kingfisher was probably a forest bird.
How does a kingfisher see a fish to dive on it?
A fishing kingfisher perches over clear, still or slow water and scans for movement. Because light bends as it passes from water into air, a fish appears to be in a slightly different place than it really is, and a diving bird has to correct for this. Kingfishers appear to learn the adjustment, and they also have a second area of sharp vision in each eye angled to look down and forward, plus the ability to switch between monocular vision from the perch and binocular vision as they close in, which helps them judge the true depth and position. When it dives, the bird enters the water almost vertically, grabs the fish, and uses its wings to swim back out.
Why is a kingfisher so brightly coloured?
The vivid blue and green of many kingfishers is a structural colour rather than a pigment. The feather barbs contain a spongy nanostructure that scatters and reflects certain wavelengths of light, producing intense blue and green that shift slightly with the viewing angle and do not fade over time as pigments do. What the colour is for is less certain. It may serve in courtship and species recognition, and against a background of dappled water and foliage the flashing blue of a flying kingfisher can be surprisingly hard for a predator to track. Some kingfishers are also boldly patterned in black, white, and rufous rather than iridescent.
Is it true a kingfisher inspired a bullet train?
Yes. When Japan's Shinkansen trains reached high speeds, a train exiting a tunnel compressed the air ahead of it into a shock wave that produced a loud boom heard hundreds of metres away, a nuisance in residential areas. An engineer on the project who was also a birdwatcher noted that a kingfisher dives from air, a thin medium, into water, a dense one, with barely a splash, because of the smooth wedge shape of its bill and head. Redesigning the front of the train to a long, tapering, kingfisher-like nose reduced the tunnel boom, and also cut air resistance and power use. It is one of the most cited examples of biomimicry in engineering.