Policy Change, Human Harvest & Control of Lesser Snow Geese
David N. Koons Asst. Professor & Lise M. Aubry Ph.D.
Once a rare spectacle to witness during migration, agricultural changes to the North American landscape have led to rapid increase (5-11% per yr) in the continental population of lesser snow geese (Chen caerulescens caerulescens) over the last 40 years. This has become a great concern because burgeoning numbers of snow geese have 1) led to increased damage of standing and fall-seeded cereal crops, 2) provided a reservoir for the bacterium that causes avian cholera, which can easily be transmitted to other bird species, and 3) caused ecosystem-level changes to their arctic breeding grounds.
To alleviate these deleterious impacts, the Arctic Goose Working Group suggested that the continental snow goose population be reduced by 50% below numbers in the late 1990s. Population modeling indicated that reductions in adult survival would have the greatest impact on population growth, and sport harvest was later identified as the most humane method for accomplishing this task. As a result, a 1998 Conservation Order amendment to the Migratory Bird Treaty allowed for the most liberal sport harvest regulations since the Treaty was passed in 1916 (spring hunt, un-plugged shotgun magazine, use of electronic calls, 100 bird bag limits).
This landmark change in North American policy seems to have reduced adult snow goose survival in southern populations; however, whether these changes will produce the desired reductions in continental population abundance is not yet known. Population momentum could cause further growth before a decline occurs, and recent reductions in survival may simply fall short of the levels needed to actually reduce long-term abundance. My post-doctoral research is focused on addressing these uncertainties using advances in mark-recapture-recovery statistics, as well as integrated matrix population models.
Management Outcomes
Using a hierarchical model, we hope to develop a mechanistic approach for directly quantifying the impact of policy changes on population dynamics that could be applied to both rare and over-abundant species. Specifically, our work should identify whether management directed through sport harvest will be able to control the continental lesser snow goose population. If not, we will be able to quantify additional changes in demographic parameters that will be needed to achieve management objectives.
