Mallard derivatives often engage in a foraging behavior that some people call “drilling.” Whenever these ducks encounter standing water, their instincts tell them that water has tendency to draw out worms and other invertebrates. The best way to capitalize on this situation is to stick their bills into the water or mud and to force the water out of through these tooth-like structures on the insides of their mouths. Any worms or invertebrates that are caught on these structures are quickly eaten.
It is almost like how baleen whales feed, but it’s done much smaller amounts of water and so rapidly that it appears as if the ducks are drilling into the at full steam.
They use this same method on the water, but on land, they can easily turn an area into a muddy morass in very short order.
This is what they left behind after only about 15 minutes drilling.