Chital group size: More about food, less about fear in predator-dominated tropical forests

Group size in ungulates is believed to reflect a balance between antipredator strategies and competition for resources. We studied chital (Axis axis) group sizes across habitat types representing variation in food availability and predator cover, along with predator density and chital density, within moist deciduous forests of Kanha National Park, India. Habitat-specific chital density was estimated using distance sampling followed by density surface modeling, while tiger and leopard densities (major predators of chital) were derived from camera-trap-based spatially explicit capture-recapture models. Group size data were obtained through systematic habitat-based surveys. We found that both chital density and typical group size varied among habitat types. Densities and group sizes were highest in grasslands (110.09 ± 41.15 per 25 km²; 18.2 ± 1.4; mean ± SE), followed by miscellaneous forests (21.97 ± 6.04; 10.3 ± 1.2; mean ± SE), and lowest in sal (Shorea robusta) forests (6.58 ± 0.60; 5.18 ± 2.2; mean ± SE). These habitat-driven differences in chital density strongly predicted typical group size, explaining 44% of its variation (R² = 0.44, p ≤ 0.001). Predator density correlated positively with chital density (r = 0.54, p ≤ 0.001), suggesting that predators tend to occur where prey is more abundant. Chital group size also correlated strongly with chital density (r = 0.66, p ≤ 0.001). After accounting for the effect of chital density on group size to reduce collinearity, predator density explained 6% (p < 0.05) of the remaining variation in chital group size, indicating a modest secondary role for predation, with the remaining variation likely driven by a combination of density-dependent and habitat-related factors. Grasslands, despite comprising only ~9% of Kanha, supported the highest chital densities and largest group sizes, indicating that they function as key aggregation areas for chital within the landscape. Maintaining these habitats is therefore important for sustaining high local chital densities. The strong relationship between group size and chital density further suggests that group size can serve as a practical, low-cost indicator of relative chital abundance.