Indicators of Adaptive Responses in Home Range Utilization and Movement Patterns by a Large Mammalian Herbivore

Abstract

GPS/GSM collars were fitted to females in two sable antelope herds occupying adjoining home ranges in the Kruger National Park in order to establish their movement responses to seasonally changing resource availability. This investigation formed part of a larger study aimed at identifying the factors responsible for the substantial population declines by this and other rarer antelope species in the protected area. To indicate responses to stressful periods during the seasonal cycle, we used the following measures: (a) proportion of locations outside the home range core, (b) displacement distances from day to day in foraging locations, and (c) extent of movement at night versus during daylight. Movements beyond the home range core were affected by excursions to water as well as foraging locations. When food and water availability became restricted during the dry season, one herd extended its range well beyond the core region favored during the wet season, while the other herd concentrated its space use more tightly within the core region, except during excursions to water. Journeys to water also affected the patterns shown by diel (24 h) displacements calculated between morning versus evening foraging locations. Diel displacement distances between evening locations were minimal when both food and water were plentifully available, and were greatest for one herd during the late dry season, but for the other herd when rainfall deficits occurred during a wet season month. Nocturnal movement showed a peak in the transition period between the dry and wet season when both resources were restricted and prevailing temperatures high. Hence, while these measures did indicate periods when resources became restricted, results revealed some of the complexities due to interactions between food and water availability. Findings also emphasised the limited extent of the landscape upon which sable depended for their resource requirements.

Keywords:

• animal movements
• core area
• GPS telemetry
• home range
• Hippotragus niger
• water restrictions