Chemical repellents can protect agricultural crops from birds by inducing conditional food avoidance learning. Moreover, untreated "observer" birds can learn to avoid foods by imitating behavioral responses of treated "demonstrators." We measured behavioral responses of demonstrators (captive European starlings, Sturnus vulgaris) to aversive unconditional stimuli (chemical repellents). We also monitored feeding behavior of treated demonstrators and untreated observers in response to the conditional stimulus (a colored food cup), which was presented for 2 hours prior to treatment. We tested n=24 pairs of demonstrators and observers to four treatments (n=6 pairs/treatment): (1) methyl anthranilate (MA), an irritant to birds, that is considered to be an environmentally and toxicologically safe food flavoring; (2) methiocarb (MC), an effective repellent that is no longer considered to be environmentally safe; (3) propylene glycol (PG), a non-repellent carrier; and (4) control (no chemical). During the training phase, demonstrator starlings were presented with a colored food cup for 2 hours, and then were provided the respective treatments. Observers fed from their normal food cups and were not handled during training. During the 2-choice learning test, conducted daily for 14 days, we provided 20 g of food in colored and uncolored cups for 2 hours to both demonstrators and observers. We videotaped starlings during both the training phase and 2-choice learning test. We used The Observer (Noldus Information Technology) to quantify activity budgets and feeding rates of demonstrators during the training phase, as well as cup preference and feeding efficiency of demonstrators and observers during the 2-choice learning test.

Chemical repellents affected activity budgets of starlings. Specifically, the control birds spent more time feeding than birds from the respective treatment groups, but the feeding efficiency (n pellets eaten/min of feeding) of controls was less than among treated starlings (p<0.05). During the 2-choice learning phase, avoidance of the colored food cup for demonstrators occurred on 5 of 14 days for controls; 7 of 14 days for PG; 12 of 14 days for MA; and 7 of 14 days for MC. Avoidance among observers occurred on 3 of 14 days for controls; 9 of 14 days for PG; 4 of 14 days for MA; and 12 of 14 days for MC.

Behavioral observations indicated that treated demonstrator starlings exhibited reduced feeding efficiency compared to controls or untreated observers (p<0.05). The data suggest that environmentally benign and toxicologically safe chemicals such as MA can induce long-term food aversion learning when the peripheral senses are bypassed. Moreover, the detailed observational data obtained in this study provide valuable insights into behavioral mechanisms and subtle social interactions between birds.

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