Feral Horses and Donkeys in the Wet/Dry Tropics: Their Sympatric Abundance, Distribution and Habitat use in Gregory National Park, N.T

Abstract

This study examines spatial and temporal aspects of the resource ecology and the ecological separation of feral horses and feral donkeys in an area of range overlap in the wet-dry tropics. An improved understanding of the adaptive strategy of the Equidae has potential applications for the management of feral populations, and the conservation of threatened native equids in their indigenous ranges. The 3195 km2 study area was located in Gregory National Park in the Victoria River District of the Northern Territory, Australia. The density, distribution and habitat use of the two species was systematically sampled by aerial survey in each of four seasons: May (cool, early dry season), August (cool, mid dry season), November (hot, humid, late dry/pre-wet season) and February (wet season). Over the four surveys, 510 horse groups and 100 donkey groups were counted within strip transects. Feral horses were more abundant and more sightable than donkeys. The surveys were designed to yield indices of relative population abundance, and the derived ratio of horse to donkey abundance averaged 4 times to 1. However, this ratio is overestimated due to the interspecific differences in sightability within the study area.