Deterrence response in a seed-eating sparrow Zonotrichia capensis (Passerine: Emberizidae) against seed common phenols

Abstract

Some seeds contain allelochemical compounds that exert a deterrent effect against seed-eating animals. Birds have the ability to recognize such compounds and can avoid their intake, thus preventing adverse or toxic effects. The diet of Rufous- collared Sparrow (Zonotrichia capensis) in the Monte desert of Argentina indicates that this is a highly opportunist bird with broad diet breadth since it feeds on seeds, many of which contain phenolic secondary compounds. The aim of this study was to evaluate the feeding responses of Z. capensis against different kinds of individual compounds that are common in seeds. We conducted two- choice feeding trials in the laboratory in order to assess two different kinds of these compounds in seeds: complex phenols (high molecular weight) such as hydrolyzable tannin, tannic acid and condensed tannins; and simple phenols (low molecular weight) such as the phenylpropanoids: cinnamic acid, caffeic acid, and ferulic acid. In the trials we simultaneously presented a control-feed of commercial foxtail millet seeds (Setaria italica) topically applied with a control solution, and a treatment-feed of foxtail millet seeds topically applied with solutions of 1% of each compound mentioned above. For those compounds with deterrent properties, we repeated the trial but used as treatment-feed of foxtail seeds topically applied with solutions of 0.5% of such compounds. Rufous-collared Sparrow consumed less of the seeds treated with two different concentrations of the tannic acid, cinnamic acid and caffeic acid than of the control seeds, and the intake of seeds topically applied with cinnamic acid and ferulic acid was the same as for control seeds. The showed deterrence suggests that Rufous collared-sparrow avoids both simple and complex phenolic compounds.