We tested the bird aversive properties of methyl anthranilate, yucca
extracts, and Xanthoxylum spp. extracts in one- and two-bottle drinking assays
that used European starlings (Sturnus vulgaris). In one- and two-bottle tests,
methyl anthranilate proved to be the more potent stimulus in producing an
avoidance response. Starlings avoided consuming Xanthoxylum and yucca
only in the two-bottle tests. Previous studies showed that yucca was a good
adjuvant in stabilizing lipophilic compounds in water. Starlings did not avoid
binary mixtures of methyl anthranilate and yucca differently from what would
be expected if they were only responding to the solution’s methyl anthranilate
content. However, yucca enhanced the aversive qualities of Xanthoxylum. The
ability to identify mode of action for repellency and synergistic combinations
of chemicals derived from natural products for use in repellent mixtures is an
important aspect of the development of cost-effective, environmentally safe
repellents for use in conflict resolution between humans and wildlife.