Flooding risk assessment for nests of imperiled shorebirds in South Texas: Raw HOBO logger data

This project aims to: 1. Assess the risk of flooding to nesting sites for Snowy Plover (Anarhynchus nivosus) and Wilson’s Plover (A. wilsonia) identified by Coastal Bend Bays & Estuaries Program (CBBEP) monitoring and 2. Identify suitable nesting areas outside the CBBEP monitoring sites that have low risk of nest flooding and recommend areas where management and conservation benefits would be highest. Populations of Snowy Plovers and Wilson’s Plovers are declining across their range, prompting their classification as Vulnerable for the Species of Greatest Conservation Need in Texas. CBBEP has been monitoring nesting Wilson’s Plover and Snowy Plovers to identify and guide management actions that could maintain or increase their nesting success, including the establishment of exclusion zones and placement of signage within recreational areas. However, effective management strategies for these species are hindered by a lack of spatial tools that identify high- and low-value areas for nesting, particularly tools that integrate quantitative assessments of flooding risk, a substantial cause of nest failure. Identifying areas with a lower risk of flooding will support the prioritization of areas for management strategies and investment and allow resources to be shifted towards areas with longer-term benefits to nesting birds. To quantify and map availability of suitable nesting habitats, we will use the existing Tidal inundation Model of Shallow-water Availability (TiMSA) developed by Calle et al. (2016). TiMSA incorporates time series of observed water levels from all NOAA tide gauges within the project area and a DEM as inputs. The study area boundary is segmented by Thiessen polygons where the area within each polygon is closer to a reference water level gauge, and the grouped study area polygon is divided into grid cells matching the resolution of the DEM. TiMSA estimates water depths in each grid cell as the difference between the elevation of predicted water levels from gauges and the elevation of the benthic surface obtained from the DEM. Then, the duration that each grid cell is inundated within a defined ecologically-relevant range (i.e., shorebird nesting elevations) is measured at defined time steps. The outputs are raster files depicting the distribution of target elevations with daily estimates of inundation and its duration. This information is then used to quantify suitable nesting areas for the two target species and develop a spatially explicit flooding risk assessment based on hydroperiod estimates. Model performance is assessed by integrating data sets of observed in situ water levels from HOBO dataloggers, field observations of nest locations and times of nesting for both species, and precipitation data. HOBO water level dataloggers will be placed using a stratified random sampling design by elevation and distance to the nearest gauge for up to 2 months, collecting barometric pressure-based water depths every 5 minutes. Bird surveys during the nesting season will be conducted to fill spatial gaps not documented by CBBEP. The location and abundance of nesting birds will be determined by GPS, following previously established methods by CBBEP. Spatial error is assessed through the agreement of observed nesting flooding events and predicted inundation estimates at each nest location. Agreement between predicted (TiMSA outputs) and observed flooding events is assessed through mixed-effects linear models, using distance to gauges and elevation as fixed effects. Precipitation data will be integrated as a random effect in the validation model as precipitation-driven flooding has been previously documented.