The Ecology of Feral Horses in Central Australia

Abstract

Feral horses in central Australia spend most of their time foraging. There was no difference between nocturnal and diurnal time-budgets. However, horses were more likely to be seen walking to water and drinking in the afternoon or evening than at any other time of the day. The overriding influence on pasture was the timing and amount of rainfall combined with the grazing of horses and cattle. The use of pastures by horses and cattle was affected by species composition of the pasture, distance from drinking water, elevation and time since the last rain-induced growth event. The extremely high variability in effective precipitation results in very unpredictable quality, quantity and location of resources for cattle and horses. Horses consistently selected a higher quality diet with a higher proportion of monocot material than cattle. Cattle appeared to more readily take perennial grasses and non-grass material than horses. Horses and cattle can both tolerate a broad range of habitats. Both show preferences for particular habitat types but in time virtually all habitats are used by both species. Flat areas with predominantly perennial pasture and frequent watering points appear more suited to cattle than horses, whereas hilly areas growing predominantly annual pasture appear better suited to horses than cattle. Social organisation conformed with the basic pattern for horses studied elsewhere in the world. Harem groups maintained relatively stable adult composition. However, as dry weather continued and pasture became dry and sparse harem group size decreased. Changes in the feral horse population predicted by a simple model based on birth, death and harvest rates corresponded well with population estimates determined by aerial survey. Horses help denude large areas, force macropods from these areas, foul water-holes with carcasses and cause accelerated gully erosion. Managers require mustering, trapping and shooting for successful control of feral horses on central Australian properties. A sufficient reduction in population size can be achieved by harvest and sale of horses even in the most difficult areas. Shooting from helicopter is vital for control of horses where harvest has failed or a quick reduction in numbers is required to alleviate impact. All control operations must be well planned and their success monitored.