Seasonal and spatial variation in the diet of an invasive deer linked to a threatened palm tree and invasive woody species in a protected area of northeastern Argentina

Abstract

Invasive axis deer (Axis axis) currently thrive along the Parana and Uruguay River watersheds in Argentina, Uruguay and Brazil. There is little information on axis deer ecology in its introduced range. We assessed seasonal and spatial variation in selected dietary items of axis deer, and tested whether the consumption of invasive woody plants and bait deployed for hunting purposes was related to their spatial availability at El Palmar National Park, home to the threatened Butia yatay palm tree. We identified macroscopically the rumen contents of 197 deer culled by controlled shooting over bait in winter and summer and by spotlighting from slow-moving vehicles in winter. Rumen contents by volume mostly contained grass and leaves in winter (95.3%) and summer (69.9%), followed by fruits/seeds of palm trees (in summer only) and invasive woody plants (mostly in winter), including honey locust (Gleditsia triacanthos), chinaberry (Melia azedarach), Chinese (Ligustrum sinense) and glossy privet (Ligustrum lucidum), and firethorn (Pyracantha atalantoides). Permutational analysis of variance confirmed that axis deer dietary composition varied significantly between seasons and hunting methods. The proportion of bait-fed deer culled by controlled shooting increased significantly with an increasing amount of bait (soybean or dry maize) deployed at each blind. The consumption of each invasive woody species was spatially aggregated and matched their core area of occupancy, suggesting localized feeding and limited short-term movement consistent with deer philopatric behavior. By providing the deer with cover, water and nutrient-dense food items, the riverine forest gains special relevance for integrated management efforts targeting both exotic woody species and exotic ungulates.