that is visible to most birds, anthraquinone is a quintessential
avoidance-conditioning agent for wild birds (Werner
et al., 2009). Werner and Provenza (2011) suggested that
an effective application strategy for avian repellents might
include initial applications of a postingestive repellent(e.g.,
anthraquinone) and subsequent applications of a visual
cue with spectral characteristics (e.g., near-ultraviolet
absorbance) sufficiently similar to the repellent (Werner,
2009).