Laser scarecrows: A potential solution to protect crops

Both lethal and non-lethal deterrents are currently available to prevent avian pests from damaging grain crops. However, lethal control using guns, traps or chemical avicides is less preferred because of the difficulties in obtaining permits and declining effectiveness as birds usually learn how to avoid lethal threats.

In addition, the use of chemical avicides poses toxic effects on non-target animal species and the environment. As a result, reports show that growers and researchers are frequently turning to non-lethal deterrents to reduce crop damage. But despite the increasing number of non-lethal deterrents on the market today, none appear to provide permanent or singular solutions to bird depredation of crops.

In this new study, researchers from the University of Florida and the University of Rhode Island in the US tested the effectiveness of laser scarecrows in reducing damage to milking-stage sweet corn by European starling birds, in a controlled experimental setting where laser and control treatments were alternated each day, allowing each flock to forage over 5 days.

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Reduction in corn damage

The researchers observed a more than 20% reduction in corn damage in the laser-treated plots. “Visible lasers emit a focused, coherent beam of light at a single wavelength, in contrast to most light sources which emit non-polarized radiation at multiple wavelengths, with varying intensities. Thus, lasers appear to frighten birds and elicit escape responses like other scaring devices. Our results, therefore, show that lasers can effectively deter crop-depredating birds,” they said.

They also observed that birds foraging on natural corn ears usually perch on wobbly corn stalks forcing them to bob in and out of the laser layer, experiencing more laser scatter and distraction, and making behavioural avoidance of laser exposure much harder for them. Just as in larger fields, it seems that natural corn makes lasers quite effective, they said.

“Due to the corn foliage, there is a lack of visibility of surroundings, and of potential predators, which elevates starlings’ perceptions of predation risk — enhancing the effectiveness of the lasers,” they said. The hope is that, if made cost-effectively, lasers have great potential as effective and non-toxic tech solutions to help growers protect their crops from bird damage, they added.

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Does distance affect effectiveness?

In this study, the scale was confined to laser effects within 30 m. The researchers found a very strong laser deterrence effect up to 20 m, and little to no deterrence at 30 m. However, according to the researchers, the effect of distance observed in their study is less important or inapplicable in real field settings, as growers in field studies note that the entire flock will simply not settle in the field after detecting a laser.

“It is, therefore, important to understand how the foraging behaviours of the birds in a small-scale pen study may differ from those of free-flying bird flocks with access to large, sweet corn fields,” they said.

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Differences in crop vulnerability

The researchers highlighted that, as with other non-lethal deterrents, laser avoidance may decline with repeated exposure, because animals get used to discomfort and distraction provided that the deterrent is not dangerous; this is called habituation. However, sweet corn is one crop that is suitable for laser deterrence because it has a narrow temporal window of susceptibility or vulnerability; sweet corn typically has less than a week between the onset of the milking stage and harvest, and this short window limits the development of habituation. The researchers reiterated that “As tolerant behaviour toward uncomfortable stimuli can develop via habituation-like processes, this requires confirming that specific individual birds withstood increasing direct exposure over time, data that we did not collect.”

Researchers also pointed out that in cases where lasers are used to deter birds from crops with long vulnerable periods, such as fruits and berries, identifying the likelihood of laser avoidance or tolerance is important.

The researchers concluded that they encourage further studies of marked individuals in pen and field settings to deepen understanding of the likelihood of laser tolerance or avoidance via habituation and sensitization.