Mode of Repellent Activity of Condensed Tannin to Quelea

INTRODUCTION Nonlethal chemical repellents are being vigorously investigated to control wildlife feeding in agriculture and silviculture and thus alleviate damages to food, feed, and fibre. Unfortunately, few effective avian repellents have emerged, partly because workers tend to be anthropomorphic in their basic assumptions about target species and repellent action (Rogers, 1978), and partly due to the lack of knowledge of the feeding behavior of the target species (McKey, 1974). Rogers (1978) advocated natural chemical defenses of plants against herbivores as starting points for studies dealing with repellent development. Rogers (1978) defined repellents as a "compound or combination of compounds that, when added to a food source, acts through the taste system to produce a marked decrease in the utilization of that food by the target species." He separated repellents into primary repellents, where the animal reacts to the taste of the repellent alone, and secondary repellents, where the animal uses the taste of the repellent as a cue to other later physiological adverse effects. Most of the successful repellents have been secondary repellents (Bullard et aI., 1983a,b), but few investigators have looked at the reasons behind the ineffectiveness of primary repellents in topical applications. Condensed tannins, which would classify as primary repellents, are the active ingredient in bird-resistant sorghums (Harris, 1969; Tipton et aI., 1970; McMillian et aI., 1972). These compounds are found in a wide variety of plants (Haslam, 1979) and elicit their herbivore, antifeedant activity primarily through an astringent tactile stimulus (Bate-Smith, 1972; Arnold and Hill, 1972). Astringency, a contracting or dry feeling in the mouth, is caused by precipitation of protein in saliva and on mucosal surfaces (Bullard et aI., 1981). Although the anti-herbivore characteristics of tannins are well known in intact plants, very little is known about the use of extracted tannins as topically applied avian repellents on plants. Bullard and Shumake (1979) recently began appraising tannins as repellents against red-billed quelea (Que/ea que/ea), which has set the stage for further research on their utility in bird damage control. The object of the research on which we are reporting was to determine the mode of repellent activity of wattle tannin to quelea. Quelea were wild-trapped in Sudan, flown to the Denver Wildlife Research Center, and held for a 90-day quarantine and acclimatization period. During this period birds were provided water, grit, and a maintenance ration mixture of whole proso millet, whole Martin X sorghum, and Purina …