Applications of chemical bird repellents for crop and resource protection: a review and synthesis

Abstract

Non-lethal repellents are needed to protect newly planted and ripening crops, to prevent valuable resources from being damaged by some wild birds worldwide. We systematically searched all scientific publications, patents and product registrations to develop a current review and synthesis regarding chemical bird repellents for wildlife researchers, ecologists, managers and conservationists. We then developed a database regarding the testing procedures and repellency results associated with the published and unpublished literature. For this comprehensive database, we developed an ‘index of success’, or relative efficacy level (e.g. effective in most experiments), associated with each tested bird repellent. We found 345 papers published in 1948–2022, including 2994 tests of 1478 repellent chemicals. From 224 publications regarding seed repellents, chemicals that were effective in most experiments and tested in three or more experiments include fungicides (cycloheximide, thiuram), insecticides (carbamates, imidacloprid), starlicide (3-chloro-p-toluidine hydrochloride), human pharmaceuticals (aminopyridine, quinine sulfate), petroleum distillate (paranapthalene), alkaloids (caffeine, quinine sulfate), monoterpenes (d-pulegone) and naturally occurring or synthetic polyphenolic compounds (anthraquinone). Among 114 publications regarding repellents used for foliar/fruit applications, chemicals that were effective in most experiments include activated charcoal, anthraquinone and carbamate. Among other bird repellents that were reportedly effective in most experiments, chemicals used for water applications and tested in three or more experiments include benzaldehyde, ortho-aminoacetophenone and sodium chloride; chemicals used as bait repellents include anthraquinone, methyl anthranilate and 2-carbamoyloxyethyl(trimethyl)azanium chloride; and the single chemical regarded as an area repellent was methyl anthranilate. There are currently 17 registered bird repellent products in the USA for five active ingredients, including anthraquinone, capsaicin, methiocarb, methyl anthranilate and polybutene. Future research and development of chemical bird repellents should include biopesticides (i.e. pesticides derived from natural materials) and pesticides that are already registered for human food use. The future discovery of repellent active ingredients and repellent products can be facilitated by an understanding of the scientific literature, patents and product registrations regarding bird repellent applications summarised in this review.