Feathers coated with 2% and 4% quinine were avoided
most. Both quinine concentrations were similarly effective. Lower concentrations (0.1%, 1%) of quinine were not
as effective. It could be suggested that concentrations of
2% and 4% quinine ingested acted as positive punishment.
Birds suffered from its noxious effects and formed
a stronger association between the quinine and the bitter
taste at these concentrations and used the taste to avoid
pulling out the feathers of the plastic model. However, it is
possible that 2% and 4% quinine was extremely distasteful
(bitter) and therefore prevented ingestion of feathers.