Fertility control for managing macropods – Current approaches and future prospects

Abstract

Macropods play an important ecological role in the Australian environment; however, at high population densities can adversely affect biodiversity and primary production and result in human–wildlife conflicts. While shooting is recognised as the most humane and species-specific method for controlling macropod populations, in peri-urban situations fertility control provides an attractive option to replace or reduce lethal interventions. An appropriate fertility control agent for managing overabundant macropods needs to provide long-lasting infertility following a single treatment, be species-specific in its action or administration method, and be safe, humane, and cost-effective. Several contraceptive methods that induce infertility for multiple years have been tested on macropods. These include surgical techniques; hormonal implants containing deslorelin, a gonadotrophin-releasing hormone (GnRH) agonist, or levonorgestrel, a progestin; and immunocontraceptive vaccines (zona pellucida vaccine and the GnRH-based vaccine, GonaCon). These methods vary in the complexity of delivery and therefore their potential for adverse welfare impacts. Minimal side effects on behaviour and health have been observed. Despite some recent progress with remote dart delivery of deslorelin implants and GonaCon, efficient deployment of all existing methods is currently restricted to either captive or small, wild populations where individuals can be approached closely enough for safe capture and treatment. Of the currently available methods, levonorgestrel and GonaCon are the most suited to population-scale management. To date, studies addressing the effect of fertility control on the growth rate of macropod populations have been limited but are essential to enable full evaluation of the efficacy and cost/benefit analysis of the different approaches. Mathematical modelling to identify the level of infertility required to meet population management goals, as well as comparing integrated management strategies, will support planning of large-scale field trials. Improving dart delivery of existing contraceptive agents and developing new methods, such as an oral contraceptive, would increase the cost-effectiveness of applying fertility control to free-ranging macropods and may make treating larger populations feasible.