Effect of primary and secondary repellents on European starlings: An initial assessment

Wildlife managers need chemical repellents that are effective at deterring damage by birds, but these repellents must be environmentally and toxicologically safe. The number of commercially available bird repellents has been reduced because of concerns about environmental safety. Currently, these are 2 categories of avian repellents. Chemicals that are reflexively avoided by birds because they irritate the peripheral chemical senses are referred to as primary repellents. Chemicals that cause gastrointestinal illness and learned avoidance of ancillary sensory cues that are paired with the illness are known as secondary repellents. Secondary repellents most often identified as the most effective avian repellents are derived from synthetic agrichemical pesticides and generally are regulated against because of their toxicity and concerns about the consequences of adding them to the environment. Primary repellents are usually derived from natural products and human food and flavor ingredients, and their use as bird repellents has been promoted as fulfilling the need for environmentally safe repellents. However, primary repellents are considered to be less potent than secondary repellents. We found that if the primary repellent, methyl anthranilate, was delivered enterically in European starlings (Sturnus vulgaris), we could achieve the same level of repellency as with the secondary repellent, methiocarb. Equal repellent effects for the 2 chemicals were found despite differences in their mode of action. Also, birds given an enteric delivery of the primary repellent methyl anthranilate showed fewer signs of behavioral distress (e.g., immobility and regurgitation) relative to those birds given the secondary repellent, methiocarb. By redirecting the site of action of a primary repellent, we have shown the feasibility to optimally combine the potency levels of secondary repellents with the biological and environmental safety attributes of primary repellents, without sacrificing efficacy. Primary repellents may be converted to secondary repellents via gastrointestinal delivery thus potentially increasing efficacy and economic viability of these chemicals. Formulations that mask the irritating qualities of primary repellents are needed so that the chemical will be freely consumed by the target animal and exert its effect in the gastrointestinal tract.