Preventing birds from perching on the sensor units of the Federal Aviation Administration's Low Level Wind-shear Alert System (LLWAS) is crucial to its successful operation. In this study we evaluated, under controlled conditions, responses of brown-headed cowbirds (Molothrus ater), fish crows (Corvus ossifragus), great horned owls (Bubo virginianus), barred owls (Strix varia), and black vultures (Coragyps atratus) to several anti-perching devices. No device was totally successful against every species. Of the 5 original test devices, the most effective perching deterrent was a set of 17 stout spikes (“AgSpikes”) secured to the central portion of the sensor unit that point up 0° to 30° from the vertical. The central spikes were subsequently redesigned and combined with 9 metal bushings (3 for each arm of the sensor unit) that fit loosely on the sensor arms and that were armed with 5 sharp spikes each. This “AgSpikes and SpikedSpinner” combination unit was as effective as the original AgSpikes for all birds except owls, which were able to place their feet within the open spaces of the redesigned AgSpike portion of the device and perch on the 3 horizontal spikes. The combination units should adequately discourage most large and small birds from perching on LLWAS sensors. The availability of alternate perches in the field will likely enhance the effectiveness of the deterrent. Monitoring performance of the combination units deployed in the field is recommended to verify that they are working as expected.
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