Maybe you've seen a scarecrow perched in a field or a plastic owl standing guard over a garden. The idea is that the decoy will scare away birds and small mammals from feasting on whatever goodies lie below. But do the fake people and pseudo-avian predators really do the trick?

Sort of, and here's why.

Scarecrows have long been the method of choice to dissuade birds from feasting on seeds and growing crops. They're often stick-like mannequins dressed in old clothes and placed in fields and gardens to ward off crows, sparrows and other hungry birds.

But one of the problems with scarecrows is they just stand there. Sooner or later, the birds figure out that the stick guy is no person because he just doesn't budge. Once they realize that, fear flies away.

"Many times they will turn scarecrows into a comfortable perch," writes Avian Enterprises, makers of a bird repellent.

Wising up to owls

This pigeon is not afraid of this plastic owl. This pigeon has gotten used to his plastic owl pal. (Photo: Eric Buemeyer/Shutterstock)

Realizing that scare-people aren't all that scary, inventors came up with new and improved decoys. They tried owls because so many birds and small mammals, like rabbits, are frightened of the winged predator.

Farmers, backyard gardeners, building managers and homeowners hang plastic owls in hopes hungry animals will recognize the owl shape and stay away. And that works, at least for a time.

A study by Linfield College found that songbirds are afraid of owl decoys. Researchers swapped out owl decoys and a cardboard box of the same size in an oak woodland within Oregon's Willamette Valley. Then measured how often birds visited feeders in the vicinity of the objects and found they were much less likely to go near the feeder when the owl decoy was stationed nearby. However, they weren't scared one bit by the cardboard box.

The birds wised up, however. After a few days, they realized the owl was fake and returned to the feeder.

Similarly, Cornell Lab of Ornithology says plastic owls hung from the eaves of a house will usually scare away woodpeckers and keep them from hammering on your home. But just like with the songbirds, that trick only works for a few days. "Birds often acclimate to the same visual stimulus in the same exact place every single day," they write.

So it's the scarecrow problem all over again. If something just sits there — no matter how frightening it appears at first glance — birds figure out it's not all that scary.

Movement is key

inflatable, dancing tube man Large farms might use dancing tube men to scare away hungry birds. (Photo: Michael Warwick/Shutterstock)

Fake owls might work if you need to keep birds or animals away from somewhere for just a day or two. Or you could move your plastic owl around your house or garden so it looks like it's real. Some people also tie it to a rope so it sways and moves, almost like it's flying.

There are also special products that move and bounce constantly to convince hungry visitors they are keeping guard.

Cornell mentions Terror Eyes manufactured by Bird-X, as an effective alternative to fake owls. These brightly colored balloons have fierce eyes that follow their prey. They bounce on a spring and move constantly so birds don't get used to them.

Some large farms have also turned to those inflatable tube men that you often see outside car dealerships. They dance and shimmy and whip their appendages all around. No bird would dare go near them.

California farmers also use shimmering aluminum PET ribbons, The Wall Street Journal reports. They're tied directly to the plants, reflecting the sun and scaring off any animal looking for a snack.

On the non-object front, people have turned to gas-powered propane cannons or flash powder to make loud noises that scare birds away from everything. But the birds get used to the sounds, too.

Deterrents in the water

shark eye stickers These eye stickers hope to trick a shark it's been spotted. (Photo: Will Creed/Shark Eyes)

It isn't just birds that are sometimes fooled by pretend predators. Surfers are finding their own decoys to try to deter sharks.

A company named Shark Eyes offers huge eye-shaped stickers that can be attached to surfboards, clothing and diving gear. The company says it, "aims to trick the shark into thinking it's been spotted, thereby removing the element of surprise and deterring an attack."

Richard Pierce, conservationist and founder of the Shark Conservation Society, tells Insider the eyes make sense as a deterrent.

"Great Whites are primarily ambush predators," he said, "and so it could be that if they were convinced their prey was observing them, they make look for an easier opportunity elsewhere."

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

Do fake owls and other decoys work?
You might be able to fool birds and bunnies with fake owls and scarecrows, but not for long.