Indicator V 2.0: Freshwater Marsh - Freshwater Marsh Birds

Freshwater Marsh Birds
This layer is one of the South Atlantic LCC indicators in the tidal and nontidal freshwater marsh ecosystem. It is an index of potential habitat for five freshwater marsh bird species.

Reason for Selection
Patch sizes of fresh marsh were ranked with knowledge of marsh bird habitat relationships. Over time, a decrease in patch size will correspond to marsh degradation and wetland loss. Brown and Dinsmore (1986) tested bird responses to wetland patch size in interior fresh marshes. They showed 10 species were not present in wetland patches of < 5 ha, but were included in greater patch sizes. Examples of these species include least bittern, northern pintail, and northern shoveler. Several other species had strongly increased abundance with patches > 5 ha. Therefore, our lowest rank (0) for wetlands was < 5 ha. The next class considered was > 5 ha and ≤ 20 ha. This patch size class is inclusive of marsh bird home ranges: King rail in fresh marsh have known home ranges of 7.7-16 ha (Pickens and King 2013); least bittern home ranges are highly variable, but Bogner and Baldassarre (2002) reported a mean of 9.7 ha and Moore (2009) showed a mean wetland area of 10.9 ha where least bittern were detected. Brown and Dinsmore (1986) showed a species richness– wetland area relationship with the greatest species richness near 20-30 ha. For king rail, Drew and Collazo (2014) also had support for a model with a patch size class of > 20 ha for predicting species occupancy. Similarly, Pickens and King (2014a, 2014b) showed water-level management, often at a scale > 20 ha, and habitat measured at a 100 ha scale, corresponded to king rail abundance. Since the indicator is dependent on the NLCD, future monitoring is feasible. A decrease in patch size will be an early sign of marsh degradation and/or wetland loss. 

Input Data
-- 2011 National Land Cover Database (2011 NLCD) 

Mapping Steps
Indicators used in Blueprint 2.0 were initially computed, or in the case of existing data, were resampled to 1 ha spatial resolution using the nearest neighbor method. For computational reasons, we then used the Spatial Analyst-Aggregate function to rescale the resolution to 200 m. The aggregate function avoided loss of detail by taking the maximum value of each cell in the conversion (e.g., species presence).

A Spatial Analyst-Region Group function was used with a 4-neighbor rule. The 4-neighbors best quantified fragmentation around patches and this rule helped eliminate misclassifications of fresh marsh (< 5 ha). Based on knowledge of the species noted above, the patch size classes (in hectares) were ranked as follows:

0 = Less potential for freshwater marsh bird presence (< 5 ha) (low)
1 = Potential presence of least bittern, Northern pintail, Northern shoveler, and others (≥ 5 and ≤ 20 ha)
2 = Potential presence of king rail (> 20 ha) (high)

55,330 patches scored a 0; 15,893 patches scored a 1; 1,799 patches scored a 2.

Defining the Spatial Extent of Ecosystems
This indicator has been clipped to the freshwater marsh ecosystem. Visit the Blueprint 2.0 ecosystem maps page for an explanation of how each ecosystem’s spatial extent is defined. 

Known Issues
The distinction between fresh and estuarine marsh was determined by the National Wetlands Inventory (NWI), but the accuracy of this data has not been documented. Other misclassifications of freshwater marsh appear to include wet pastures or grasslands and wet areas planted with winter wheat. The amount of open water within freshwater marsh (i.e., open water-vegetation edge), and the wetland's hydroperiod, are critical to wildlife, but the ephemeral nature of water in this ecosystem makes it difficult to measure with currently available GIS data.

Indicator Overview
The South Atlantic ecosystem indicators serve as the South Atlantic LCC's metrics of success and drive the identification of priority areas for shared action in the Conservation Blueprint. To learn more about the indicators and how they are being used, please visit the indicator page. Check out the Blueprint page for more information on the development of the Blueprint, a living spatial plan to conserve our natural and cultural resources.

Literature Cited
Bogner, H. E., and G. A. Baldassarre. 2002. Home range, movement, and nesting of least bitterns in western New York. Wilson Bulletin 114:297-308.

Brown, M., and J. J. Dinsmore. 1986. Implications of marsh size and isolation for marsh bird management. The Journal of wildlife management:392-397.

Drew, C. A., and J. A. Collazo. 2014. Bayesian networks as a framework to step-down and support Strategic Habitat Conservation of data-poor species: A case study with king rail (Rallus elegans) in Eastern North Carolina and Southeastern Virginia, Prepared for the United States Fish and Wildlife Service Raleigh Field Office.

Homer, C.G., Dewitz, J.A., Yang, L., Jin, S., Danielson, P., Xian, G., Coulston, J., Herold, N.D., Wickham, J.D., and Megown, K., 2015, Completion of the 2011 National Land Cover Database for the conterminous United States-Representing a decade of land cover change information. Photogrammetric Engineering and Remote Sensing, v. 81, no. 5, p. 345-354. 

Moore, S., J. R. Nawrot, and J. P. Severson. 2009. Wetland-scale habitat determinants influencing least bittern use of created wetlands. Waterbirds 32:16-24.

Pickens, B. A., and S. L. King. 2013. Microhabitat selection, demography, and correlates with home range size for the king rail (Rallus elegans). Waterbirds 36:319-329.

Pickens, B. A., and S. L. King. 2014a. Linking multi-temporal satellite imagery to coastal wetland dynamics and bird distribution. Ecological Modelling 285:1-12.

Pickens, B. A., and S. L. King. 2014b. Multiscale habitat selection of wetland birds in the northern Gulf Coast. Estuaries and Coasts 37:1301-1311.