Researchers equip scarecrows with lasers to reduce crop damage

Researchers have recently published a new study revealing that scarecrows with laser technology can be an effective bird deterrent.

Efforts to frighten birds from eating crops or congregating where they aren’t wanted have been fruitless for centuries. In The Wizard of Oz, the kindly scarecrow lacked a brain, and birds flocked to sit on him.

More recently, managers of a hotel with a swimming pool on its roof that is adjacent to The Jerusalem Post’s building on Jaffa Road were at their wit's end when pigeons, starlings, and crows came to drink, bathe, and leave their guano in the water next to bathers. They purchased wooden statues of scary birds and installed them around the pool. In a few minutes, the smart avians that realized they didn’t move and weren’t alive perched on their heads. Damage to crops caused by birds costs huge amounts of money in countries around the world. Now, researchers from the University of Florida and the University of Rhode Island suggest that laser scarecrows – a high-tech solution using light to deter birds – can be effective.

Hi-tech, low-tech

In a new study published in Pest Management Science under the title “Experimental assessment of laser scarecrows for reducing avian damage to sweet corn,” the team presented 18 captive flocks of free-flying European starlings (Sturnus vulgaris) with fresh ears of sweetcorn and demonstrated that devices emitting a moving laser beam can significantly reduce damage to the crop up to 20 meters from the laser device.

Wildlife ecology and conservation Prof. Kathryn Sieving at the University of Florida explained that more and more growers are seeking inexpensive and portable laser units like the ones tested in the research. “Growers need big effects for affordable prices, and if they can spend $300 to $500 each for lasers to protect large fields for up to three weeks instead of more expensive options such as hiring people to patrol with dogs, falcons, or rifles, then lasers would be beneficial,” she said.

One reason why lasers provide a particularly effective solution for the protection of sweet corn is the short timeframe before harvest in which birds would target the crop, known as the ‘vulnerability window.’ This short window reduces the risk of birds becoming desensitized to the lasers.

Sieving explained that lasers are being explored widely for crops with short vulnerability windows like sweet corn. They seem to be performing very well, especially when different non-lethal deterrents, like lasers with loud noises, are combined. Birds attack sweet corn only during the brief ripening phase (called the milking stage), and this lasts only five to 10 days. So, as soon as it ripens, harvest begins. Therefore, in sweet corn, the protection does not need to last very long, and lasers seem to be working well; this reduces damage during milking stages by far more than 20%, they said.

The study involved two types of trials – stick trials in which fresh sweet corn ears were mounted on sticks at varying distances from laser units and natural trials in which birds foraged on ripe corn grown from seed in a flight pen. Laser and control treatments were alternated each day over five days, allowing the researchers to assess the birds’ response to repeated laser exposure.

“We designed the stick trials to increase the sample size for more robust results. Natural corn matures over several weeks but then is only attractive to birds for two weeks – so our planted crop was not going to give us enough sample size. With the stick corn experiments, we could study small-scale effects and amp up the sample sizes,” Sieving explained.

Simple yet effective

The results showed that lasers reduced sweet corn damage marginally in stick trials and dramatically in natural trials. Explaining this difference in effectiveness, Sieving noted that “the sticks we presented corn on were sturdy, and the birds would sometimes perch and feed on corn while avoiding the laser layer. Natural corn stalks are flimsy, though, and the birds would be bouncing in and out of the laser layer with no control. Thus, just as in larger fields, it seems that natural corn makes lasers quite effective.”

The researchers also examined how distance from the lasers affected the amount of damage to the sweetcorn. They found that there was effective deterrence up to 20 meters from the laser source, but beyond this distance, damage to the crop increased, with little to no deterrence at 30 meters. Sieving noted that “the data showing that relationship with distance is really the only data of its kind and was possible to get because we did the work with captive birds.”

However, she explained that in true field settings, this effect seems to be unimportant. “In open fields, birds will simply leave a field that has detectable laser protection, and they fly far out of its influence. It seems that just one laser per field can often do the trick to keep most birds out, so the fine-scale spatial effects might apply only if birds were overly committed to feeding a small area – then a grower may need to add a couple of laser units with overlapping ranges.”

Sieving hopes that laser scarecrows can offer a sustainable solution for the protection of crops with short vulnerability windows. “Lasers are silent, unlike acoustic deterrents like loud bangs and other noises occurring several times per hour that can be very annoying to neighbors and workers. Lethal deterrents require permits and time and labor to apply, and the potentially toxic secondary effects on wildlife, soil, and water are often unacceptable.”