Doctoral research project: Population regulation of wild horses in the Burragorang Valley
PhD student: Andrea Harvey (veterinarian)
Supervisor: Dr Daniel Ramp, University of Technology Sydney
The management of wild horses is a controversial topic that is positioned around two central ideas: a) that wild horses negatively impact on ecosystems; and b) that their populations grow rapidly. Combined, these ideas suggest that prevention of population growth is a key management goal for regions where conservation values are viewed as being impacted.
Despite previous research on wild horses throughout the world, there remains a considerable knowledge gap on how wild horses interact with, and impact upon, other species, particularly in ecosystems where horses are novel and recent constituents. While the documentation of how, when and why wild horses impact on conservation values is important, how populations grow and are regulated is vital for understanding their ecology and behaviour. Regulation in wild horses, however, remains an elusive component of wild horse research, as there is very little scientific data on how populations regulate themselves under different circumstances. Regulation processes should differ between arid and temperate regions, between areas of varying habitat availability and quality, and when regulation is influenced by trophic interactions. The outcome of these processes should determine the difference between maximum annual potential fecundity and lifetime reproduction success, a limitation that should vary spatially and temporally. This information is currently missing from conservation decision-making and wild horse management.
Limitations to population growth in wild animal populations can be driven by environmental and climatic heterogeneity and competition and predation from other fauna that shape the trophic cascade. No research has been performed in an Australian setting regarding the roles of bottom-up regulation through sociality and resource availability and top-down regulation through predation in horses. Clearly, knowledge of the behavioural and population ecology of wild horses is essential to maintain confidence in population projections and potential targets for management intervention. Robust quantitative methods are required to evaluate the effectiveness of any interventional modality aimed at limiting population growth.
Horses in the Burragorang Valley
The horses occupying this region are thought to have originated from the Shetland Islands, and were used as pit ponies in past mining operations. Previous culling kept the total population density low, but culling is currently prevented for political reasons. Their range currently comprises several nearly-isolated populations related to the topography of the landscape, with geographical constraints on movement restricting movement centred around riparian corridors. The landscape is heterogeneous and access to resources varies spatially. The current population is estimated to be approximately 60 horses consisting of about 10 herds. There is currently no information on what limitations, if any, are influencing reproduction. Hence, the capacity of the high quality riparian corridors to act as source habitat to re-populate surrounding habitats is currently unknown.
Study aims and objectives
This doctoral research project proposes to examine the population and behavioural ecology of wild horses in the Burragorang Valley. Assessments will be made to evaluate the carrying capacity of the area, quantifying limitations to population growth, interactions with other species, and the influence of habitat availability and quality on density dependent habitat selection. The goal will be to develop an understanding of metapopulation structure that can be used as a basis for robust decision-making. As Burragorang is a water catchment of significance, this research will determine the importance of the riparian corridors and flood-out zones for the horse population, enabling an assessment of the contribution of horses to nutrient loading. This will provide information on potential influences on water quality.
Wild horses will be surveyed using a combination of on-ground surveys, camera traps, and faecal samples to assess:
- Population-level and herd-level demographics and con-specific interactions;
- Distribution, movement, and habitat selection;
- Distribution and density of faeces as an estimate for relative abundance and habitat use ;
- Carbon isotope signatures and DNA metabarcoding of faeces to investigate dietary dynamics to determine the proportion of grazing that occurs in riparian corridors;
- Nitrogen isotope values and multi-elemental analysis of faeces to provide insights into the effects of horse faeces on ecosystem nutrient cycles; and
- Presence of faecal pathogens.
Parallel to this research in the Burragorang Valley, a veterinary study will be carried out on semi-wild horses housed at a sanctuary to evaluate the efficacy and behavioural effects of an immunocontraceptive agent as a means of providing additional regulation control where necessary. Data from the behavioural ecology study will be combined with the immunocontraceptive study to model metapopulation trajectories for a range of management alternatives.
Project update 3rd March 2016