Date of this Version
Secondary repellents have been demonstrated to effectively reduce avian crop depredation. However, these compounds frequently are toxins and there are concerns about environmental safety. Many primary repellents are toxicologically and environmentally safer, but these chemicals are not as effective when traditional delivery methods are used. We set out to determine whether the difference in efficacy of primary vs. secondary repellents was due to differences in potency of the chemical classes or site of action within the animal. We hypothesized that the efficacy of primary repellents could be enhanced if they could be delivered directly to the gastrointestinal system, thus by-passing the peripheral senses. Our experiments were conducted on captive European starlings (Sturnus vulgaris). We showed that by-pass of the peripheral senses via oral gavage enhanced the efficacy of 2 hydroxyacetophenone (2HAP), a primary repellent. However, we found that starlings were sensitive to changes in their visual environment, and that learned avoidance to a colored food cup could be mitigated by changing the cage door of the test system. Topical application of repellents to foods allowed starlings to selfmediate their exposure to the repellents. We found that methiocarb and methyl anthranilate (MA), a primary repellent, both induced food aversion learning, but 2HAP did not. Detailed analyses of feeding behavior elucidated the mechanistic differences between Methiocarb, MA, and 2HAP. Methiocarb induced gastrointestinal illness in starlings, which resulted in post-ingestive suppression of food intake, and subsequent food aversion learning. Some starlings with MA in their food also developed gastrointestinal illness, and food aversion learning. Starlings with 2HAP in their feed did exhibit reduced feeding efficiency, but these starlings did not develop gastrointestinal illness or food aversion learning. These experiments demonstrate that the location and intensity of illness are of paramount importance to induce food aversion learning.