- 1). Wait two months to see what colors their adult feathers are. Female mallards are mostly brown with some streaking of white and black. Their heads and undersides are a little paler. Male mallards have heads of solid dark green and chests of solid brown, while their body and wing feathers are similar to a female's, except with white predominating. The appearance of any distinctively male plumage lets you know what the gender is.
- 2). Check the tail. As a male mallard matures, it develops a distinctive clump of curly feathers around its tail.
- 3). Vent the duckling if you need to know the gender before its adult plumage starts to show. Hold the duck on its back in your hand, head toward you. Find the vent, the opening under the tail.
- 4). Hold the tail away front the vent, and use a thumb and index finger to apply gentle, steady pressure on each side of it. Take care to avoid hurting the duckling. You should be able to squeeze the vent open.
- 5). Wipe away any liquid that the duckling emits when you apply this pressure, and examine the genitalia. The male has an open circular fold of skin that holds a penis. The female has a similar circle, but it is semiclosed with the skin folded up. It's possible that the muscles of the vent are constricted. Wait, and with continued pressure from your thumb and forefinger, these should relax. If not, it is impossible to tell the duckling's gender.