Cockatiels (Nymphicus hollandicus) reject very low levels of plant secondary compounds

The rejection thresholds of caged cockatiels (Nymphicus hollandicus) were tested to determine their sensitivity to plant secondary compounds. Both alkaloids and tannins were tested using a two-bottle method in which purified water was always available in one bottle and an aqueous test solution was available in the other bottle. After each 3-day experimental period, three consumption parameters were recorded (test solution-side consumption, water-side consumption, and a ratio of test solution-side consumption to total consumption). Repeated test periods were conducted with increasingly concentrated test solutions of each compound until one or more consumption parameters were significantly (P<0.05) affected. The results demonstrate that cockatiels prefer purified water to 100 μmol l⁻¹ quinine, 1000 μmol l⁻¹ gramine, 500 μmol l⁻¹ hydrolysable tannin, and 10,000 μmol l⁻¹ condensed tannin. These thresholds for secondary compounds were determined at concentrations that were 16–3900-times more dilute than the thresholds detected for salts and sugars. Moreover, in contrast to the generalization that taste acuity is poorer in birds than in mammals, the data demonstrate that the granivorous cockatiels actually reject quinine at lower concentrations than phytophagic mammals. These findings support the hypothesis that cockatiels use taste to detect, monitor, and possibly avoid intake of potentially toxic compounds.