Waterfowl disturbance in California and Nevada (2018)

Long-term environmental management to prevent waterfowl population declines is informed by ecology, movement behavior and habitat use patterns. Extrinsic factors such as human-induced disturbance can cause behavioral changes which may influence movement, and resource needs, driving variation that affects management efficacy. To better understand the relationship between human-based disturbance and animal movement and habitat use, and their potential effects on management, we GPS tracked 15 dabbling ducks in California over about 4-weeks before, during and after the start of a recreational hunting season in October and November 2018. We recorded locations at 2-minute intervals across three separate 24-hour tracking phases: Phase 1) two weeks before the start of the hunting season (control (undisturbed) movement); Phase 2) the hunting season opening weekend; and Phase 3) a hunting weekend two weeks after opening weekend. We used GLMM models to analyze variation in movement and habitat use under hunting pressure compared with normal observed patterns prior to commencement of hunting. We also compared responses to differing levels of disturbance related to the time of day high - lethal); moderate - non-lethal (crepuscular); and low - night). During opening weekend flight (percent time and distance) more than doubled during moderate and low disturbance and increased by 50 percent during high disturbance compared with the pre-season weekend. Sanctuary use tripled during moderate and low disturbance and increased 50 percent during high disturbance. Two weeks later flight decreased in all disturbance levels but was only less than the pre-season levels during high disturbance. In contrast, sanctuary use only decreased at night while daytime doubled from 45 percent to greater than 80 percent, although not to pre-season levels. Birds adjust rapidly to disturbance and nocturnal foraging compensates energy deficits. These results have implications for energetics models that estimate population food requirements and management may benefit from reassessing the juxtaposition of habitat to optimize wetland management for waterfowl.