The influence of predator exclosures and livestock grazing on duck production at Bear River Migratory Bird Refuge, Utah.

摘要

Nest predation is a major factor impacting duck production and recruitment on breeding areas in North America. I surveyed waterfowl managers employed by the U.S. Fish and Wildlife Service and U.S. state wildlife agencies to determine their beliefs about nest predation and its management. Over 64% of respondents believed that rates of nest success on their management units averaged 30% between 1996–2000. Managers believed habitat management and direct predator control were the most effective techniques to reduce nest predation. The construction of predator exclosures around nesting habitat also has been recommended to reduce nest predation. Between 1999–2001, I evaluated the effectiveness of 4 predator exclosures to enhance duck nest success at Bear River Migratory Bird Refuge, Utah. During this period, rates of nest success in the exclosures were slightly higher than that within control plots, but still 15%. Although published guidelines commonly recommend predator fences ≤117 cm in height, I observed red foxes jump the 114-cm-high fences. Additional research is needed to identify effective predator fence designs.; Wildlife managers have argued that periodic disturbance of vegetation should be a component of management on waterfowl breeding areas. Although many techniques are available to manipulate vegetation, grazing by domestic livestock has been controversial. Some researchers have reported that livestock grazing is detrimental to nesting ducks whereas others have argued that it can be beneficial. I evaluated the impact of a short-duration, high-intensity winter livestock grazing program on duck nesting at Bear River Migratory Bird Refuge. Following a winter grazing treatment, I measured visual obstruction on both grazed and ungrazed plots during the spring nesting season. Although visual obstruction readings on grazed plots were lower than those on rested sites early in the nesting season, those differences diminished as the season progressed. Winter grazing may impact early-nesting ducks like mallards ( Anas platyrhynchos), but not late-nesting species like cinnamon teal (Anas cyanoptera) and gadwall (Anas strepera). In designing grazing programs to manage nesting cover, managers should consider their waterfowl production goals, the composition of breeding duck populations, type of grazing system, and climatic conditions.