The primary prey of tigers across much of Southeast Asia has been depleted, reducing the ability of already limited habitat to support tigers. To better understand the extent to which two of the largest prey species, gaur (Bos gaurus) and banteng (Bos javanicus), contribute to the tiger’s diet, we estimated the average size of these species killed by tigers. This information is needed to more accurately calculate biomass of these species in the tiger’s diet and to devise strategies to increase tiger carrying capacity where habitat is fragmented and limited in west-central Thailand. We used temporally clumped locations of 24 satellite radio-collared tigers to identify their kill sites and obtained mandibles from 82 gaur and 79 banteng. Kills were aged by teeth eruption sequence, sectioning the M1 molar and counting cementum annuli. Of all gaur killed, 45.2% were adults; of all banteng killed, 55.7% were adults. The average weight of banteng killed was 423.9 kg, which was similar to the 397.9 kg average weight for gaur. The mean weight of both prey species is 3.5 to 4.5 times greater than the predicted 1:1 preferred prey to predator ratio. In the absence of medium-sized prey, killing these larger animals may be especially critical for female tigers provisioning nearly independent young when male offspring are already larger than the mother. This is the first study to present data on the average weights of gaur and banteng killed in Southeast Asia and these results suggest that these are key prey species to target in tiger prey recovery efforts.

At kill sites (15 00’- 15 40’ N, 99 00’- 99 25’ E) we collected the lower mandible of each gaur or banteng for aging. We determined sex of adult animals based on the configuration of horns (Ahrestani, 2018). The ages of calves and juveniles were determined by teeth eruptions sequence (Dyce, Sack & Wensing, 2009).  For adult prey, we extracted the first molar from the mandible, washed the tooth in water, decalcified it in a weak acid solution (HNO3 5%), and finally rinsed it again in water to stop decalcification (Klevezal1996; Spinage 1976). Each molar was then dehydrated in isopropyl alcohol, frozen and sectioned with a microtome to create 15-20 µm longitudinal cross section slices that were mounted on a glass slide. Slices were stained with Giemsa blood and labeled; stained sections were subsequently examined at 10x magnification and cementum annuli were counted (Figure 3). We concluded that the local single rainy season resulted in a single annuli pattern in western Thailand and confirmed this by comparing annuli data to horn patterns.