Deer overabundance in the USA: recent advances in population control

Abstract

During the 20th century, deer (Odocoileus spp.) populations in many parts of the USA changed from locally extirpated to locally overabundant. In 1997, two comprehensive books were published on deer overabundance to help wildlife professionals understand the complex biological, ecological, sociopolitical, public, and legal issues associated with managing overabundant deer. Since then, there have been several advances in dealing with deer overabundance, which have been briefly summarised in this review article. Most notably, since 1997 ecologists have more definitively characterised the ecological consequences of chronically overabundant deer populations, not merely in terms of direct impacts on plant communities but also in terms of cascading effects on animal communities. While still acknowledging the complexity of the interactions that affect ecosystem services and states (e.g. top-down pathways, bottom-up forces, disturbance regimes), ecologists now believe that the presence of an apex predator can affect the density, as well as behaviour and physiology of ungulates, and thereby help maintain the natural structure and functioning of plant communities. In some situations, wildlife researchers in the USA have restored native predators or documented adaptive responses by colonising predators, both of which have helped reduce locally overabundant deer populations and helped restore plant community diversity. On the wildlife policy front, some state wildlife agencies have enacted new programs to manage overabundant deer in protected areas and in urban and suburban settings. Examples include special permits for lethal removal of urban deer, as well as public hunts using special weapons (e.g. crossbows) or sharpshooting programs to control deer in state parks. A better understanding of the human dimensions associated with deer overabundance has helped many agencies define appropriate public education programs. However, despite these efforts to educate stakeholders about deer overabundance, there have been legal challenges associated with programs designed to control deer populations in some suburban communities. Some nongovernmental organisations (NGOs) have implemented award-winning, classroom-based educational modules to help children learn how to live with deer. Some NGOs also have stressed the importance of hunting as an ecological service. Still other NGOs have worked to facilitate linkages and cover liability concerns to enable bowhunters to help control deer in suburban communities. There also have been major advances in the potential for managing overabundant deer with fertility control, including the recent approval of an immunocontraceptive vaccine for use in deer (GonaCon™). In summary, wildlife biologists now understand the complex issues associated with deer overabundance better and there are more ‘tools in the chest’, both in terms of agency policies and management procedures than in 1997. Yet, human dimensions, public education, and stakeholder concerns continue to be the most challenging aspects of managing deer overabundance. Therefore, this issue likely will continue to confront wildlife professionals for many decades to come, whether in the USA or other parts of the world.