The Nilgiri tahr (Hemitragus hylocrius) is an endangered mountain ungulate endemic to the Western Ghats in South India.  I studied the status and ecology of the Nilgiri tahr in the Mukurthi National Park, from January 1993 to December 1995.  To determine the status of this tahr population, I conducted foot surveys, total counts, and a three-day census and estimated that this population contained about 150 tahr.  Tahr were more numerous in the north sector than the south sector of the park.  Age-specific mortality rates in this population were higher than in other tahr populations.  I conducted deterministic computer simulations to determine the persistence of this population.  I estimated that under current conditions, this population will persist for 22 years.  When the adult mortality was reduced from 0.40 to 0.17, the modeled population persisted for more than 100 years.  Tahr used grasslands that were close to cliffs (p <0.0001), far from roads (p <0.0001), far from shola forests (p <0.01), and far from commercial forestry plantations (p <0.001).  Based on these criteria I mapped the suitability of tahr habitat using a GIS and estimated that only 20% of the park area had >50% chance of being used by tahr.  I used the GIS to simulate several management options to improve the quality of tahr habitat.  Suitable habitat for tahr increased two-fold when roads within the park were closed to vehicular access.  Similarly, removal of commercial forestry plantations also resulted in a two-fold increase of suitable habitat, and finally when both road access was restricted and commercial forests were removed, suitable tahr habitat increased three-fold.  I used micro-histological analysis on tahr fecal pellets to determine food habits.  Grasses constituted 64.2% of their diet.  Five plant species (Eulalia phaeothrix, Chrysopogon zeylanicus, Ischaemum rugosum, Andropogon sp., and Carex sp.) accounted for 84.6% of their diet.  These species were found in higher densities in the grasslands of the north sector than the south sector of the park (p <0.001).  Predators such as leopard (Panthera pardus) and tiger (Panthera tigris), killed and consumed tahr.  The densities of these predators were higher in Mukurthi than in other protected areas in India.  Tahr constituted 56% of the leopards’ diet and 6% of the tigers’ diet.  I estimated that leopards and tigers in the park killed and consumed 30 to 60 tahr per year, and this accounted for 19% to 38% of the tahr population.  The tahr population in the park has undergone a decline, but it is unclear if the decline can be attributed to a single factor or the combined effect of high mortality from predation and poaching, and loss of habitat.