We studied factors affecting the ability of common brushtail possums (Trich
osurus vulpecula) to regulate their intake of a dietary toxin, jensenone, e
xtracted from Eucalyptus leaves. Increasing concentrations of jensenone in
the diet led to a dose-dependent decrease in food intake best described as
an exponential decay. Animals that had not previously been exposed to jense
none ate significantly more when first offered food containing the compound
than on subsequent days. However, when offered the same amount of food in
a number of portions throughout the night, naive animals ate significantly
less than animals offered the total meal at once. When offered food contain
ing jensenone over a 13-day period. the animals' intake varied cyclically w
ith relatively high food intakes followed by relatively low intakes. Furthe
rmore, animals that were exposed to cold conditions (4 degrees C) ate more
than those maintained at 18 degrees C but this difference was abolished whe
n jensenone was included in the diet. We interpret these results as showing
that regulation of toxin intake by common brushtail possums depends on lea
rned responses that can override other important influences on feeding.