The logic and evidence underpinning the KMP is valid but the conservation culling components of the plan are properly adaptive and will be refined as the results of current research and monitoring reduce uncertainty about key parameters such as target densities.
Unmanaged kangaroo populations reduce the biomass of ground-layer vegetation which has adverse impacts on some other native species. Therefore culling kangaroos is a valid management action. The current management ensures sustained populations of kangaroos at densities that purport to allow more vegetation and more secure populations of threatened native species.
There is published evidence that the current target density of kangaroos (set by modelling at 1 per hectare) does benefit other native plants and animals but managers recognise there are gaps in understanding the details of how temperate grassland ecosystems work as components of it (mostly kangaroo numbers) are manipulated. Current projects conducted by ACT staff and PhD studies underway at ANU should fill some of these knowledge gaps.
One key question is whether the density of 1 kangaroo per hectare is the ‘correct’ target for all times, all nature reserves and under all environmental and biological conditions. We suspect it will be too high (100 large herbivores per km2 is still a very high density relative to other systems and species, and certainly constitutes no threat to the sustainability of the kangaroos). The results of an ACT project currently being conducted will will help identify whether the average density set is the best or at least within the optimal range of densities.
Each nature reserve is a sort of habitat island with a variety of assets and threats, with varying degrees of connection between the reserves. The KMP might be supported with a set of individual site plans, with kangaroo management as but one action within each plan. Site-specific monitoring will allow management to be fine-tuned.
ACT managers have two options to lead to this site-based approach. They can nominate a number of nature reserves to be managed to allow the rare native species to be maintained with resilient populations and achieve it as efficiently as possible (cost minimisation). Or they can set a fixed annual budget and determine how many nature reserves can be effectively managed within the budget (benefit maximisation).
The methods being used to count kangaroos and estimate densities are sound, but we recommend the following four changes. (i) direct and sweep counts need more replication, (ii) uncertainties in components of direct, sweep and pellet count methods should be addressed in analyses, (iii) a team of trained professionals (i.e. staff and/or contractors) should be the core for all counts, although we acknowledge the wider social and public relations benefits of including volunteers, and (iv) the counts should be conducted as close as possible to the intended cull. Further, consideration should be given to conducting a second post-cull count perhaps six months later, at least in a subset of reserves.
Sweep counts have several potentially significant problems, including traffic problems if kangaroos flee the counters. We recommend ACT consider either replacing this method with direct or walked-line transects, or if this is not possible to use core trained staff as above.
It would be valuable to conduct a trial to compare the costs, accuracy, and precision of the four counting methods across different habitat types and kangaroo densities.
The methods used to conduct kangaroo counts should be described in standard operating manuals that can be updated as required. This would ensure continuity for a program that will have to be sustained long after current staff have left.
Publication of research by ACT staff and others should be facilitated because this work is potentially of high standard and of interest to a wider audience, as well as providing ACT decision-makers and other stakeholders with the confidence of peer review.
We thank the ACT Territory and Municipal Services Directorate for support during our visit to Canberra.
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