True Metabolizable Energy of Submersed Aquatic Vegetation for Dabbling Ducks

Sarah E. Vanderhorst, Heath M. Hagy, John W. Simpson, Chris N. Jacques

Research output: Contribution to conferenceOther

Abstract

We developed a spatially-explicit waterfowl agent-based modeling program (SWAMP) to evaluate alternative landscape scenarios in the Sacramento Valley, CA arising due to urban expansion, drought, and concordant shifts in water allocation priorities. Scenario 1 represents the current management regime, while all other scenarios consider increased urbanization and/or moderate to severe drought. Scenario 2 examines the effects of drought, but with wetland restoration goals being met and current rice acreage; Scenario 3 examines the impact of wetland restoration not being met; and Scenario 4 examines the effect of extensive idling of rice acreage. Scenario 5 represents a worst-case situation with expansive urbanization, wetland restoration goals not met, and extensive rice acreage idled. We used SWAMP to simulate the foraging activities, time activity budgets, lipid reserves, and mortality of 1.2 million ducks under each scenario. In SWAMP, birds select and consume food in patches at a rate that is dependent on the density of food on that patch, modeled as a type II functional response. Birds leave patches based on current energy stores and patch depletion, modeled as an approximation of the marginal value theorem. We parameterized the model using published values for true metabolizable energy (TME) of foods, metabolic rates and expenditures under different activities, lipid metabolism and conversion, and food storage capacity. Models were run for 180 simulated days – the duration of time over which most waterfowl overwinter in the Central Valley. Our results indicate that rice idling due to restricted water supplies would have the greatest impact on body condition and survival of waterfowl. Under Scenarios 4 and 5, birds entered into energy deficit by late December and mortality rates escalated exponentially (assuming birds did not leave Butte Basin). Failure to meet wetlands restoration goals was not as severe if those acreages remained in rice, but energy deficits and mortality increased substantially if rice acreage was instead idled. Our study helps inform managers of the potential implications of restricted water conditions in CA using a novel spatially-explicit agent based modeling approach.
Original languageEnglish (US)
StatePublished - 2016

Keywords

  • INHS

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    Vanderhorst, S. E., Hagy, H. M., Simpson, J. W., & Jacques, C. N. (2016). True Metabolizable Energy of Submersed Aquatic Vegetation for Dabbling Ducks.