Every Halloween, scarecrows become standard lawn decor. Trick-or-treaters might find them frightening, but what about the birds that these effigies are supposed to repel?

Apparently, some avians dislike them more than others. A series of tests conducted in 1980 found that small ponds near which a scarecrow was planted saw a 95 percent drop in visits by local ducks. On the other hand, certain species don’t seem to notice them. During the 1930s, wildlife scientist K.R. Lagler sent one scarecrow adrift on a floating buoy at a West Virginia fish hatchery. While most birds steered clear of the thing, he noted that it failed to deter kingfishers.

Let’s forget about bodies of water for a moment. After all, most people associate scarecrows with cornfields rather than ponds or fisheries. So, how good are they at protecting crops? Not very—unless you’re willing to put some extra effort into them.

While traditional, motionless scarecrows do work against “pest birds” (e.g. crows and blackbirds), the effect is almost always temporary. Over time, the birds get used to stationary dummies and resume their destructive habits.

However, a few tricks can up your scarecrow’s game. Researchers have learned that those with realistic facial features and brightly colored clothes are slightly better at shooing away birds. Also, moving a scarecrow around every few days often helps.

According to several studies, flailing models get the very best results. In 1989, one scientist reported that a “human-like mannequin” which occasionally lurched upwards via a double propane cannon managed to keep four-to-six acres of sunflowers safe from blackbirds.

Future farmers may have plenty of high-tech options to choose from. A robotic alternative known as the “Agrilaser” randomly deploys sweeping laser beams and, so far, the reviews are pretty good. “The system is noiseless,” says farmer Arnold Bosgoed (who’s been testing it out), “and the birds do not seem to get used to the laser beam. The installation was easy and requires no maintenance.” Another contraption—the solar-powered “digital scarecrow”—detects nearby animals with an infrared eye that surveys 178,000 square feet. When a critter gets too close, it’s warded off with a harmless supersonic wave.

Now there’s one scarecrow that won’t be asking for a brain anytime soon.