Feeding responses of red-winged blackbirds to multisensory repellents

The concept that combinations of aversive stimuli are more repellent than the individual components is familiar but has been subject to little critical experimentation. In this study, we evaluated the effectiveness of aural (alarm call), visual (red dye), and chemical (methyl anthranilate and methiocarb) stimuli for reducing consumption of brown rice by captive red-winged blackbirds (Agelaius phoeniceus). The species-specific alarm call was ineffective, as was red dye beyond an initial neophobic response. Of the stimulus combinations tested, only 0.005% (g/g) methiocarb plus red plus methyl anthranilate proved more effective than the most effective individual component stimulus. The 0.025% methiocarb and 0.025% methiocarb plus methyl anthranilate treatments suppressed consumption effectively and also caused subsequent presentation of untreated brown rice to be avoided. Our findings suggest that for repellent applications to seeded crops and ripening grains the use rate of an illness-inducing agent such as methiocarb can be substantially reduced if paired with a deterrent colour and a chemical irritant.