Managing eastern grey kangaroos (Macropus giganteus) in peri-urban areas: Developing a novel contraceptive delivery system and assessing welfare outcomes from lethal and non-lethal management

Abstract

Eastern grey kangaroo populations have become overabundant in some areas due to artificial water sources, food availability and predator removal. Evidence-based strategies are needed to manage these populations and minimise human-wildlife conflict. In this thesis, a remote dart delivery system was developed to apply Suprelorin® contraceptive implants to females. Its effectiveness and duration were assessed in three populations, comparing remote delivery with hand injection at different doses (4.7 mg or 2x 4.7 mg). Comparable efficacy and duration were achieved regardless of dose or delivery method. Welfare impacts were investigated in a fourth peri-urban population, whereby changes in behaviour, physiology, and movement patterns following treatment were assessed. Neither method triggered a stress response or affected behavioural indicators of stress or pain, showing remote delivery to be more practical and cost-efficient. Fertility control may be perceived as having fewer adverse welfare impacts, but there are some logistical challenges in implementing this strategy in free-ranging peri-urban populations. Consequently, culling remains the most frequently used method of population control, despite concerns about the welfare of conspecifics left alive. Here, the welfare impacts of culling, disturbance, and control treatments were investigated in seven kangaroo populations. Stress hormone concentrations decreased after culling, suggesting it did not induce physiological stress in survivors. Future studies should address logistical challenges such as creating longer-lasting contraceptives, enhancing methods for identifying treated animals, and developing protocols to assess welfare impacts. Furthermore, larger sample sizes and additional stress measures should be considered. This thesis provides evidence-based recommendations for management strategies that benefit kangaroos, humans and the environment, while also considering the welfare implications of these strategies.