FACULTATIVE BEHAVIOR IN UNPREDICTABLE ENVIRONMENTS - MOBILITY OF RED KANGAROOS IN ARID WESTERN-AUSTRALIA

1. Australia's arid zone is characterized by unpredictable extremes in climate, and abundance and quality of biotic resources. Ecological theory and definitions derived from relatively stable environments in the northern hemisphere do not fit well in Australian deserts. We illustrate this by describing a range of moving behaviours of 46 radio-collared red kangaroos in the Gascoyne region of Western Australia, which we believe are facultatively employed to maximize survival in arid environments. Tracking occurred every 2 months on average during the last 6 months of a 23-month long drought and for the following 27 months. 2. Home range size was highly variable and averaged 18.4 +/- 5.0 km2 for adult females [MAP(95) +/- 1 SEM] and 36.1 +/- 17.2 km2 for adult males. These home ranges are the largest recorded for this species and are attributed to inherently poor vegetation production and the occurrence of drought. 3. Adult males were significantly more mobile during the drought. Their mean interfix distance (MID) was 8.4 km during the drought and 2.2 km thereafter. This may have been a consequence of local food shortage, as implied by a negative correlation between adult male mobility and pasture biomass. High mobility may also reflect males monitoring the oestrus status of females. This may be a necessary outcome of a lack of oestrus synchrony in red kangaroos, which we suggest is a consequence of temporal and spatial irregularity of resource availability in this arid environment. 4. Adult and sub-adult females remained relatively sedentary throughout the study (adult female MID 4.2 km during drought, cf. 2.5 km thereafter). Sub-adult females averaged 2.8 km during the drought. Conserving energy for lactation and reducing juvenile mortality by maintaining familiarity with resource distribution may explain site fidelity in females. 5. There was evidence of innate dispersal in sub-adult males that was independent of climatic conditions. They ranged over an area of 72.8 +/- 55.5 km2 [MAP(95)], but did not occupy a defined home range. 6. It would appear from this versatility in behaviour that conventional definitions of behavioural 'norms' or 'home ranges' that exclude occasional excursions from main areas of use do not accommodate all of the biological needs of animals such as red kangaroos. Attempting to fit traditional definitions of home range probably obscures rather than clarifies the ecology of animals which include irregular and temporary environmental dispersal in their behavioural repertoire.