Spatiotemporal Modeling of Shorebird Habitat Availability at Rankin Wildlife Management Area, Tennessee

This study examines spatiotemporal patterns of shorebird stopover habitat availability at Rankin Wildlife Management Area (Rankin Bottoms) on the Douglas Reservoir, Tennessee, USA. Rankin Bottoms is a key stopover site for fall migrating shorebirds traveling through the Tennessee River Valley (TRV). In the TRV, the majority of shorebird habitats consist of mudflats created along reservoirs in the fall as the Tennessee Valley Authority (TVA) lowers reservoir levels to prepare for winter and spring rains. Occasional changes to the annual reservoir management cycle enacted by TVA have affected the timing of mudflat exposure and thus the timing of availability of stopover habitats for migrating shorebirds in the TRV.

I used high-resolution LiDAR elevation data of the lake bottom along with recorded reservoir stage values from 1972 to the present in a Geographic Information System (GIS) to model mudflat exposure at Rankin Bottoms. I defined model parameters that allow me to report values for shorebird habitat availability as it changes through the migration period, and modeled these values for three reservoir management scenarios including the current management scenario. I used average reservoir stage data for the 1972-1990 and 1991-2003 reservoir management scenarios and predictive reservoir stage data for the current ROS management regime as input into this model. My results suggest that changes made in 1991, and more so in 2004, delay the creation of habitat at Rankin Bottoms to the beginning of August, but extend habitat availability further into the winter. Under the most recent management scenario implemented by TVA in 2004, the 15 species of shorebirds known to potentially arrive in the TRV in July will find their habitat at Rankin Bottoms inundated upon their arrival. Based on these models, shorebird-optimal reservoir management guidelines have been prepared for TVA to consider as part of their adaptive management plan.

The findings of this study are presented in the Rankin Wildlife Management Area Shorebird Habitat Viewer, a visualization tool, which offers 3-Dimensional animations of habitat availability at Rankin Bottoms. Using this tool, interested parties can compare and contrast the amount of available habitat for any day of the migration period under the historic and current management regimes.

The models generated for this study can help TVA’s reservoir managers to assess the habitat impacts of proposed reservoir management activities now and in the future. The methods developed in this study are not specific to the phenomenon of shorebird migration or to the TVA river system. They may be used by reservoir and wildlife managers elsewhere to assess the habitat consequences of different management strategies and ultimately determine the optimal management strategy for species of concern.