Invasive species are regarded as one of the largest threats to biodiversity but little is known about the invasion of exotic plants into the tropical forest. The per cent grass availability in gaur (Bos gaurus H. Smith, 1827) foraging areas in three different habitats namely dry deciduous forest, moist deciduous forest and thorn forest in relation to weed category areas viz., Lantana camara invasion areas, Chromolaena odorata invasion areas, 'both weeds invasion' and 'weed-free' areas were investigated in Mudumalai Tiger Reserve between November 2003 and April 2004.