American Avocet, photo by Michael Gray.

Shorebird and Waterfowl Use Of Moist-Soil Management Units in Balmorhea

Ryan Anthony, Ryan O'Shaughnessy, Ryan S. Luna, and Dan Collins (USFWS)

Moist-soil managed wetlands historically created for waterfowl have also created food and habitat opportunities for shorebirds. Shorebirds feed primarily on invertebrates produced in moist-soil wetlands. To maximize shorebird use at the Sandia Springs Wetlands in Balmorhea, Texas, we assessed invertebrate biomass and water quality parameters.

From our examination, we found water depth and temperature were the best predictors of shorebird presence at Sandia Springs Wetlands. To maintain a precise level of water, we recommend the use of screw-type water control gates at the wetlands. These gates control the flow of water rather than the level; by controlling the inflow and outflow rate of water, managers can maintain constant water levels.

In arid wetlands, lack of vegetation cover likely speeds up evaporation, thus requiring higher usages of water. Disking can be a valuable tool for managing vegetation; however, frequent disking can reduce invertebrate diversity, richness, and in some cases biomass. We recommend that disking be conducted immediately after spring drawdowns and only in years that it is absolutely necessary.

At the study site, we found very little biomass of invertebrates within core samples. The combination of low invertebrate biomass and low vegetative foods may be a limiting factor for shorebird usage of Sandia Springs Wetlands. We recommend vegetation in these refugia should be left standing to provide cover and habitat for invertebrates.

Overall, we recommend a water level of at least 4 inches should be maintained in the wetlands year-round to provide maximum submersion of vegetation and maximum water volume to be utilized by invertebrates as habitat. Similarly, a deeper level of water (i.e., 6–12 in.) should be maintained during the winter to make it more conducive for use by waterfowl.

Since shorebirds are present at Sandia Springs Wetlands primarily during late spring and summer, we recommend management for waterfowl should be conducted for migrating waterfowl during the fall and winter. These recommendations could also be applied to similar desert wetlands, as they are an important stopover for many wetland bird species.

Funding source: U.S. Fish and Wildlife Service.