Kangaroos avoid eating seedlings with or near others with volatile essential oils

Preliminary studies indicate that western grey kangaroos browse seedlings of non-Myrtaceae species rather than Myrtaceae. Seven morphologically-matched species pairs of Myrtaceae/non-Myrtaceae placed at three field sites showed that kangaroos avoided the essential-oil-containing Myrtaceae, but readily consumed the matched essential-oil-lacking non-Myrtaceae. The one exception (Pittosporaceae) had limited herbivory and was later found to possess two essential oils in its leaves. Gas chromatography and mass-spectra showed the seven Myrtaceae plants contain between 2 and 9 essential oils in their leaves, particularly the highly volatile monoterpene, 2,5-dimethyl-3-methylene-1,5-heptadine. Three of the above species pairs were used to gauge their effectiveness as nurse plants for a highly palatable legume. Plants placed beside Myrtaceae nurse plants were less browsed than those placed beside non-Myrtaceae nurse plants. We conclude that western grey kangaroos use olfactory cues to avoid foliage containing potentially toxic essential oils, and that this also has implications for seedling recruitment patterns in regenerating communities.