Well, not very, it turns out, unless you're willing to put up some extra effort. While traditional motionless scarecrows do work against pest birds like crows and blackbirds, the effect is almost always temporary. Over time, the birds get used to the stationary dummies, and then they resume their destructive habits. However, a few tricks can help you put your scarecrow back in the game. Researchers have learned that those with realistic facial features and brightly colored clothes are slightly better in shooing away the birds