In one sentence, describe what the following article is about:

During the mating season, male ducks will have very bright coloration in their plumage to attract mates. After mating season, the male duck will molt and lose his bright coloration and resemble a female.  Mallard ducks are sexually dimorphic, which means the males and females look different to each other. The females are brown and relatively dowdy, whereas the males have a vivid purple sash on the wings and are iridescent colors. The male Canvasback has solid white to light gray plumage. His female counterpart has plumage that is grayish-brown.  The male Wood Duck has gray feathers with blue markings on the wings during mating season. The female's plumage is usually grayish-brown.  Male and female Mottled Ducks have similarly colored feathers, making it difficult to tell them apart by plumage alone. Bill color is another way to tell the difference between a male and female duck. In many duck species, the bill color does not change during mating season, so this physical characteristic will stay the same throughout the year.  In Mallards, the male duck has a bright yellow bill and the female has a brown and orange bill.  In Mottled Ducks, the male duck has a bill that is a solid olive green to yellow color. The female's bill is brown to orange with dark splotches.  Male Wood Ducks have a red bill that has a patch of yellow at the bottom.  During mating season, the bill of the Ruddy Duck changes to a bright baby blue. Across species, male ducks tend to be larger than female ducks. In addition to have a larger body size in general, male Mallards, Rouens, and Welsh Harlequins, have larger heads and thicker necks than the females. Male ducks will have an upwardly curled feather near the tail; this is known as the ‘sex feather.' This feather, which will become noticeable in male ducks when they are between two and four months old, remains after molting. Females do not have a sex feather. Female ducks tend to have a loud and hard quack. The quack of male ducks is usually soft and rough. If you have ducks as pets and you are comfortable handling them, you can gently hold the duck by its tail until it quacks.  The sound of a quack can be used to differentiate between male and female ducks from the time that ducks are about one month old.  In Muscovy ducks, the female's quack sounds like a trill or a coo. A male Muscovy will make a quack that's very deep and breathy (sounds like 'huch-uch-uch').  The female Grey Teal makes a quack that sounds like a cackling noise, which differentiates it from the male Grey Teal.

Summary:
Observe the duck's plumage (feathers). Observe the bill color. Look at the duck's size. Look for a curled feather near the tail. Listen to a duck's quack.