This indicator is a continuous index of habitat suitability for four shorebird species.

Reason for Selection

This index represents a variety of ecosystem features and the species selected are already being monitored for the entire region by state and Federal agencies. The relative use of beach habitat by shorebird species for nesting, foraging, and breeding is an indicator of beach quality.

Input Data

Wilson’s Plover and American Oystercatcher

Betsy Von Holle (University of Central Florida) led a project that included state waterbird biologists in the South Atlantic: Tim Keyes, Felicia Sanders, Sara Schweitzer, and Janell Brush. They mapped habitat suitability based on nest, or breeding pair, density per beach segment, as was used for Von Holle et al.’s sea turtle research. The approach is documented in Von Holle et al. 2018.

The following nesting years were used for the analysis:

–American oystercatcher: FL (2005-2011), GA (2010-2011), SC (2008), NC (2007)

–Wilson’s plover: FL (2005-2011), GA (2010-2011), SC (2009-2011), NC (2007)

Least Tern

The point locations and number of least tern nests, or breeding pairs, were provided by waterbird biologists from each state’s natural resource department (Tim Keyes, Felicia Sanders, Sara Schweitzer, and Janell Brush). All least tern locations were buffered by 1 km. Although least tern do not actively forage on the beach itself, the buffer characterizes habitat selected by least tern (i.e., beach width, predator abundance, etc.) and accounts for interannual variability in nesting locations. Among years, data showed least tern often shifted the location of nests in the general vicinity of previous years.

Piping Plover (Winter Distribution)

The 2011 winter population census of piping plover was provided by the U.S. Geological Survey, as the international census is repeated every five years. Locations were buffered with a 2 km radius. Although home range estimates exist for piping plover, (Cohen et al. 2008, Drake et al. 2001) these measures depict primarily linear habitats. We used a 2 km buffer, as this is similar to the mean linear distance of 4.2 km that piping plover moved during winter in Texas (Drake et al. 2001). The resulting buffer was also substantiated by maps in Cohen et al. (2008).

Mapping Steps

1) Von Holle et al. used a categorical habitat suitability ranking based on six quantiles of nest density, or breeding pair density, for each species on the Atlantic Coast. We converted these to numeric rankings ranging from 0 (absent) to 6 (high density). We expanded the approach by ranking least tern nest abundance in the South Atlantic geography based on quantiles (0–6). Piping plover individuals were also ranked by quantile (0–6).

3) 2) The beach bird index was developed by using the software program Zonation with the core-area algorithm and without the edge removal option (edge removal = 0). Zonation starts with all potential beach habitats and iteratively removes each cell that results in the least loss of species. The rankings (0–6) described above were used as a measure of relative abundance for all species; no connectivity options were used. The values in this layer represent relative use of habitat for beach nesting birds in the South Atlantic. Fundamentally, areas with higher values in this layer have greater abundance of beach nesting birds in the index than areas with lower values.

This indicator was initially computed at a 100 meter spatial resolution using the nearest neighbor method. We then used the ArcGIS Spatial Analyst-Aggregate function to rescale the resolution to 200 meter resolution (previous versions of the Blueprint were at 200 meter resolution). The aggregate function avoided loss of detail by taking the maximum value of each cell in the conversion (e.g., species presence).

For use in the 2020 Blueprint, these data were resampled from 200 meter resolution down to 30 meter resolution because the optimization software we use (Zonation) requires all inputs to have the same raster resolution.

Final indicator values

The final indicator is continuous, with values ranging from:

High: 100 (Most important for bird index species (American oystercatcher, Wilson’s plover, least tern, and piping plover))

Low: 0 (Least important for bird index species)

Known Issues

– Beach bird survey data are summarized by beach segment and do not account for variations in density within those segments.

– Volunteers often collect beach bird data in discrete time frames and survey effort may differ by location. Some areas may not have been surveyed or nests may have been missed. Therefore, this data does not imply absence of species.

– Because we did not have the exact quantile breaks used for habitat suitability on the Atlantic coast, different methods between Atlantic and Gulf regions of this indicator may cause issues when comparing scores.

– Red knot is not included due to lack of data.

– This indicator does not capture variations in beach bird use of dune areas inland of beach segments.

– The spatial resolution of the source data has been degraded. While this layer has a 30 m resolution, it was not created directly from the spatially precise input data. Here, we resampled the 200 meter resolution data used in the previous version of the indicator back down to 30 meter resolution so that we could use it in our optimization software.

Disclaimer: Comparing with Older Indicator Versions

There are numerous problems with using South Atlantic indicators for change analysis. Please consult Blueprint staff if you would like to do this (email hilary_morris@fws.gov).

Literature Cited

Cohen, J.B., Karpanty, S.M., Catlin, D.H., Fraser, J.D., Fischer, R.A., 2008. Winter Ecology of Piping Plovers at Oregon Inlet, North Carolina. Waterbirds 31, 472-479.Drake, K.R., Thompson, J.E., Drake, K.L., Zonick, C., 2001. Movements, habitat use, and survival of nonbreeding Piping Plovers. The Condor 103, 259-267.Von Holle, B., Irish, J. L., Spivy, A., Weishampel, J. F., Meylan, A., Godfrey, M. H., Dodd, M., Schweitzer, S.H., Keyes, T., Sanders, F., Chaplin, M. K. 2018.. Effects of future sea level rise on coastal habitat. The Journal of Wildlife Management 9999. https://wildlife.onlinelibrary.wiley.com/doi/epdf/10.1002/jwmg.21633