Improved Methods for Deterring Cliff Swallow Nesting on Highway Structures

Abstract

Cliff swallows (Petrochelidon pyrrhonota) are migratory birds that frequently nest on highway structures, such as bridges. Because cliff swallows are protected by the Migratory Bird Treaty Act of 1918, nesting control methods must not harm cliff swallows or disturb active nests. This can cause delays for maintenance divisions of state departments of transportation, resulting in additional cost. In a multiyear project, we evaluated the effects of bioacoustic deterrents and bridge surface modifications on nesting behavior of cliff swallows. We used cliff swallow alarm and distress calls as bioacoustic deterrents (hereafter, broadcast calls [BC]) because they previously had been shown to delay the onset of nesting. We used low-friction plastic sheeting (PTFE, commonly called by its trade name, Teflon®) and silicone-based paint for bridge surface modification. In 2007, swallows were able to complete nests on silicone paint, but did not successfully complete any nests on PTFE. In 2008, PTFE+BC treatment significantly reduced nesting compared with no treatment, although some nests were completed at PTFE and PTFE+BC sites on the bare concrete next to the sheeting or at locations where sheeting had peeled away. We recommend treatment with PTFE+BC to reduce the likelihood of cliff swallow nesting on bridge surfaces, but this should be supplemented with weekly site visits to check treatment integrity and to remove any partial nests on untreated surfaces.

Keywords

• alarm call
• bioacoustics
• bridge
• cliff swallow
• distress call
• human–wildlife conflicts
• nest
• petrochelidon pyrrhonota
• surface modification
• teflon
• transportation