There are no odor repellents presently available. Chemical roost repellents (polybutenes, sticky pastes, sprays) have not been proven effective. Unless a suitable nesting site is almost entirely covered with repellent, swallows will still be able to land, gain a foothold, and begin nest construction. A sticky repellent may actually be counterproductive by improving nest adherence. Cliff swallow nests built over a sticky repellent have been observed. Since state pesticide registrations vary, check with your local Cooperative Extension office for information on possible repellents. The best method to prevent nest building is exclusion. Remember that swallows are a federally protected species. Permits are required for any kind of lethal control or nest disturbance activity. Disturbance is usually defined at the point at which eggs appear in the nest, so knocking down nests as they are being constructed is an effective technique. Check with your state wildlife officials about how they interpret this law.
Resources: (online)
Swallows
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