The adult Mallard drake has a beautiful green metallic green head when it catches the light, a white collar, yellow bill, rich red-brown breast, finely-marked light grey body,
bright blue wingflash (speculum) and curly tail. The Mallard is a ubiquitous wild duck prevalent in most parts of the world.
"It was this big . . ."
The Mallard is the ancestor of most domestic and many wild ducks, is promiscuous and can produce fertile hybrids with many related species.
"My halo has fallen"
The blue speculum
Mallard pair, as often with ducks, the female is much plainer so she's camouflaged when on eggs and with young.