Avoidance of plant secondary compounds by European starlings: citronellyls

There is an ongoing need for nonlethal and environmentally safe vertebrate repellents for a variety of uses. One promising source of candidate repellents is plant secondary compounds, many of which have evolved to defend against invertebrate herbivory. In this study I tested six citronellyl compounds that are used in the human flavor and fragrance industry. Testing was conducted with an invasive and exotic avian pest species in North America, the European starling (Sturnus vulgaris). All six compounds tested were highly repellent to the birds and repellency was similar across treatment days. A dose-response experiment revealed that two of the six compounds, citronellyl acetate and citronellyl butyrate, tended to be repellent at lower concentrations (chow treated with 0.1:1 mixture of the citronellyl in ethanol) than the others (1: 1 mixture). One compound, citronellyl valerate was also tested for within-day secondary repellency but no evidence was seen for this. It can be concluded that some plant derivatives are suitable for use as avian repellents and many other plant secondary compounds are promising resources for new and safe vertebrate repellents. (C) 2004 Published by Elsevier Ltd.