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Methods for excluding cliff swallows from nesting on highway structures.
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  • Abstract:
    Cliff swallows (Petrochelidon pyrrhonota) are colonially breeding migratory birds that frequently nest on highway

    structures. Protected by the Migratory Bird Treaty Act of 1918, nesting control methods cannot harm swallows or active

    nests. This causes problems and delays for structures and maintenance divisions of many departments of transportation.

    Two aversion strategies, bioacoustic deterrents and surface modifications, were evaluated for their effect on cliff swallow

    nesting behavior. The bioacoustic deterrents (BC) consisted of sonic devices that broadcast 8 unique recordings of alarm

    and distress calls. Surface modification consisted of plastic sheeting with a low coefficient of friction. In year 1, surface

    modifications with high density polyethylene (HDPE) sheeting were mounted on the vertical surfaces at typical nesting

    locations. Twenty-eight bridges in the Sacramento Valley of California were used to test the aversion strategies, using a 22

    factorial design with 7 replicates. In year 2, silicone-based paint and polytetrafluoroethylene (PTFE, commonly called

    Teflon) sheeting were evaluated as surface modifications. Nine bridges were divided into three treatment groups: control

    (no treatment), silicone paint, and PTFE. In year 3, 15 bridges were divided into three treatment groups: control (no

    treatment), PTFE, and PTFE+BC. Each year, completed nests were counted on a weekly basis for several months. In year 1,

    both broadcast calls and HDPE treatments reduced the number of nests built at a site, but neither treatment nor the

    combination completely stopped nesting. In year 2, swallows were able to complete nests on silicone paint, but did not

    successfully complete any nests on PTFE. Silicone paint was determined to be an ineffective surface modification. In year

    3, nests were completed at all control sites, and several PTFE and PTFE+BC sites. Nests built at sites with PTFE or

    PTFE+BC were never started on the PTFE sheeting itself, but instead on the bare concrete and next to the sheeting or at a

    location where sheeting had peeled away from the surface. Altogether, these tests indicated that only PTFE was wholly

    effective in preventing cliff swallows from building on a treated surface, however nests were still completed at non-covered

    locations on the bridge surface or at locations of failed sheeting attachment. Broadcast calls (BC) reduced the number of

    completed nests by delaying the onset of building, but did not stop nest construction altogether.

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