Shaped like bowling pins with webbed feet and a beak, Indian runners are some of the most efficient egg layers and meat producers of all duck breeds, making them one of the best ducks for the farm pond. Although they can all look very much alike, it's fairly easy to tell which duck is male and which is female from their physical build, feathering, and even coloration.
Listen to their voice
You don't need to try to catch or pick up an Indian runner duck to know which is male or female — they'll happily tell you. Females, known as ducks or hens, make the typical "quack quack" sound. The hens quack loudly and proudly, as the sound is used to summon their ducklings, attract mates, and otherwise communicate over long distances.
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Female ducklings start quacking at 4 or 5 weeks old, but you might notice a difference in sound before then. Like male ducklings, females make a peeping sound, but it is sometimes interspersed with a strange coughing sound that denotes a developing quack. Boy ducklings have a monotone peep that is completely unpunctuated by any other sound. Indian runner drakes stay rather monotone as they become mature. Their low, whispery grunts make them far quieter to keep than their noisier female counterparts.
Foot the bill
Indian runner drakes have a paler, pinker bill and usually paler feet as well. The female duck has a bright yellow or orange beak, sometimes with spots of black pigment as she grows older. By contrast, a male has a paler bill that is pinkish in color.
Male Indian runners are larger than the females, so they will have larger feet with thicker legs to support their larger bodies. Their legs will also be longer, as they need to straddle the female duck during breeding. When Indian ducklings hatch, the males usually tend to outgrow the females right from the start. They'll develop longer legs, bigger feet, and more widely spaced legs within the first few days and weeks.
Note the feathers
You might notice that some adult ducks have a curly feather on their tail and others do not. The curly feather is known as a drake feather, and it develops when a male is sufficiently mature enough to mate. A hen's tail has feathers that are uniform across the back. The top feathers lay down flat and do not curl. When spread, the tail feathers are uniform in size and form an even, rounded edge.
Feathers can also be useful in sexing ducklings. Young hens develop feathers quicker than males. Both sexes have papery thin wings when they hatch out of the egg. The female's wings will start plumping within hours, and the first wing sprouts will erupt along their edges within just a few days. This is a good time to put leg bands on those that you observe as potential females should you wish to keep track of the gender of your ducklings.
Indian runners can be bred to produce female ducklings that are chocolate in color. The sex-linked coloration is based on using a chocolate-colored drake, who has two copies of the chocolate gene. When bred to a non-chocolate female, he will pass on the chocolate coloration to his daughters only.
Sex-linked Indian runners are available online, making it easy to name your new ducklings and observe the physical attributes and sounds of each gender while knowing who's who. Keep in mind that future generations of mixed colors won't follow the sex-link pattern since their genetics are different, and you will have males and females of mixed colors.