Spatial and numerical relationships between Pampas deer (Ozotoceros bezoarticus celer) and feral pigs (Sus scrofa) in the Bahía Samborombón Wildlife Refuge, Argentina

Abstract

Ozotoceros bezoarticus celer, the southernmost subspecies of pampas deer and endemic to the Argentine Pampas, is seriously endangered. In Buenos Aires Province, the last Pampas deer population is located in the Bahía Samborombón region. Poaching and the increase in exotic species such as feral dogs and feral pigs have been suggested as the most important causes affecting the recovery of the deer population. Thus, the aim of this study was to analyze the spatial and temporal variations in distribution and abundance of the Pampas deer and the feral pig in the Bahía Samborombón Wildlife Refuge and to discuss the possible consequences of the interaction between these species. Six aerial surveys were conducted during 2002-2005. A total of 747 deer and 2690 feral pigs were counted, with a slight decrease in the deer sightings and an important increase in pig sightings during the sampling period. Estimated density ranged between 0.63-1.56 individuals/km2 for deer and from 0.91 to 7.78 individuals/km² for pigs. A negative correlation was found between densities of the two species (r_s =-0.83; P=0.04), and the distributions are not mutually independent. A progressive change in distribution has been detected in the Pampas deer population during the last three decades. This study provides evidence of the potential existence of negative interactions between Pampas deer and pigs. Due to the critical situation of the Pampas deer population, a control plan for feral pigs should be developed and urgently implemented to prevent the increase and expansion of this population to the south of the Samborombón bay, and consequently, to reduce the potential competition and predation on the existing deer population.