Browsing by Author "Sieges, Mason L."
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Item Estimating Waterfowl Carrying Capacity at Local Scales: A Case Study From Edwin B. Forsythe National Wildlife Refuge, New Jersey(Journal of Fish and Wildlife Management, 2018-01-29) Ringelman, Kevin M.; Williams, Christopher K.; Castelli, Paul M.; Sieges, Mason L.; Longenecker, Rebecca A.; Nichols, Theodore C.; Earsom, Stephen D.The management of wintering North American waterfowl is based on the premise that the amount of foraging habitat can limit populations. To estimate carrying capacity of winter habitats, managers use bioenergetic models to quantify energy (food) availability and energy demand, and use results as planning tools to meet regional conservation objectives. Regional models provide only coarse estimates of carrying capacity because habitat area, habitat energy values, and temporal trends in population-level demand are difficult to quantify precisely at large scales. We took advantage of detailed data previously collected on wintering waterfowl at Edwin B. Forsythe National Wildlife Refuge and surrounding marsh, New Jersey, and created a well-constrained local model of carrying capacity. We used 1,223 core samples collected between 2006 and 2015 to estimate food availability. We used species-specific 24-h time–activity data collected between 2011 and 2013 to estimate daily energy expenditure, morphometrically corrected for site- and day-specific thermoregulatory costs. To estimate population-level energy demand, we used standardized monthly ground surveys (2005–2014) to create a migration curve, and proportionally scaled that to fit aerial survey data (2005–2014). Crucially, we also explicitly incorporated estimates of variance in all of these parameters and conducted a sensitivity analysis to diagnose the most important sources of variation in the model. Our results from an outlier-removed, a strict depletion model indicated that at estimated mean levels of supply (923 million kcal) and cumulative demand (3.4 billion kcal), refuge food resources were depleted before November. However, a constant-supply model that represented tidal replenishment of resources indicated that just enough energy was present to sustain peak winter populations. Variation in model output appeared to be driven primarily by uncertainty in population abundance during peak periods of use, emphasizing a new management focus on studying migration chronologies of waterfowl. This model allows for relative assessment of biases and uncertainties in carrying-capacity modeling, and serves as a framework identifying critical science needs to improve local and regional waterfowl management planning.Item If you flood it, they will come: auantifying waterbird response to the Migratory Bird Habitat Initiative(University of Delaware, 2014) Sieges, Mason L.In response to the Deepwater Horizon oil spill, the Natural Resources Conservation Service implemented the Migratory Bird Habitat Initiative (MBHI) in fall 2010 to provide temporary wetland habitat for migrating and wintering waterfowl, shorebirds, and other waterbirds that might be impacted by oiled wetlands along the northern Gulf of Mexico. Using weather surveillance radar, I conducted regional assessments of bird response to shallow-water flooding on privately-owned agricultural lands within the Mississippi Alluvial Valley (MAV) and the West Gulf Coastal Plain (WGCP) from fall 2010 through spring 2011. I also conducted a more focused analysis on MBHI sites in Louisiana where different management regimes were directed at specific waterbird taxa during different seasons and management was conducted over multiple years. Specifically, mudflat and shallow water habitats were created to benefit migrating waterfowl and shorebirds in the fall and spring while fields were flooded to greater depths in winter to supply wintering waterfowl with food and cover. I detected increases in diurnal bird density at the onset of evening flights over managed sites relative to the two prior (unmanaged) years as well as compared to concurrent bird densities over non-flooded agricultural lands in the surrounding landscape. Changes in bird density matched seasonal shifts in waterbird distributions and abundance with the greatest observed densities corresponding to the arrival of wintering waterfowl in December. Record flooding in the two years prior to implementation of the MBHI coupled with a region-wide drought during management years complicated the quantification of changes in remotely-sensed soil wetness on sites. Specifically in Louisiana, bird use of MBHI sites was greatest just after the onset of flooding on mudflat sites in the fall. Across regions and seasons, bird response was generally related to the land cover composition of the site and the surrounding landscape (i.e., amount of emergent marsh and agriculture) and/or the proximity of the sites to high density bird concentration areas (e.g., large waterfowl populations on refuge lands such as Laccassine NWR in Louisiana). The relationship that bird density had with landscape variables differed depending on region and season. In general, I detected greater increases in relative bird use at sites in close to areas of high bird density during winter in both the MAV and WGCP. Bird density was also greater during winter at sites with more emergent marsh within sites and in the surrounding landscape. By enrolling lands located near high density bird areas and within existing wetland complexes, future conservation programs could maximize bird use of managed wetlands. Weather radar observations suggest that waterbirds used temporary wetland habitat provided by the MBHI within the Mississippi Alluvial Valley and the West Gulf Coastal Plain regions in the wake of a major environmental disaster.