Constructed Wetland Habitat for American Avocet and Black‐Necked Stilt Foraging and Nesting

Abstract

In 1994, a 117‐ha wetland was designed, constructed, and operated by the Tulare Lake Drainage District (TLDD), California, USA, to provide foraging and nesting habitat for American avocets (Recurvirostra americana) and black‐necked stilts (Himantopus mexicanus). The wetland was operated seasonally in compliance with regulatory requirements to compensate for impacts to stilts, avocets, and other wildlife exposed to elevated selenium concentrations, fluctuating water levels resulting in nest flooding, and high nest‐predation rates at the TLDD agricultural drainage evaporation basins. Water supply for the wetland was from low‐selenium (typically <2 μg/L) saline agricultural drainage water, although the facility also had capability to blend and use freshwater and saline supplies. Coincident with wetland construction, 2 evaporation basins totaling 1,174 ha were physically modified and operated to discourage their use by shorebirds. In the first year of wetland operation (1995), American avocet and black‐necked stilt nest construction at the wetland was 17.6 nests/ha. This compares to a preproject (1994) combined density of 1.9 nests/ha at the evaporation basins. From 1995 through 2004, annual nesting attempts by American avocets and black‐necked stilts at the wetland averaged 2,896 per year (24.8 nests/ha). American avocets and black‐necked stilts represented 91% of the nests observed at the wetland. Over the 10‐year monitoring period, nest success at the wetland averaged 82% for American avocets and 75% for black‐necked stilts. We estimated nest predation rates at the constructed wetland to be <1%. During the same period, American avocet and black‐necked stilt nesting at the evaporation basins declined from 2,266 in 1994 to 9 in 2004. The constructed wetland has proven to be effective in attracting and providing suitable nesting habitat for large numbers of avocets and stilts. Results of this long‐term study confirm the validity of management recommendations for American avocets and black‐necked stilts and suggest that agricultural drainage can be successfully managed to provide highly productive managed wetlands.

Population and Habitat Objectives for Breeding Shorebirds in California's Central Valley

“…We examined the range of breeding densities observed for stilts and avocets in each of the four planning regions in both semi-permanent wetlands and rice (Table 3) and proposed an initial hypothesis that a 50% increase of the overall average density of each species in semi-permanent https://doi.org/10.15447/sfews.2017v15iss1art3 wetlands in the Central Valley could be achieved through enhanced management of existing wetlands and restoration of high-quality wetlands. Though it is unclear how much of an increase in breeding densities can be reasonably achieved throughout the Central Valley, very high densities have been achieved locally in wetlands managed exclusively for breeding shorebirds (Davis et al 2008) and in private wetlands (2015 email from C. Hickey, Point Blue Conservation Science, to K. Strum, unreferenced, see "Notes") in the Tulare Basin. An emphasis on habitat enhancement to achieve higher densities may minimize the total extent of restoration required and, potentially, be a more efficient use of resources.…”

“…The TLDD wetland provides an example of how modifying contemporary wetland management can improve nesting habitat for breeding shorebirds and increase nest success (Davis et al 2008), and could be used to weigh trade-offs of large-scale wetland restoration with smaller-scale intensively managed wetland units. This approach may also help alleviate the strain that large-scale wetland restoration would put on an already limited water supply.…”

Wintering ecology of sympatric subspecies of Sandhill Crane: Correlations between body size, site fidelity, and movement patterns

“…Modifications to discourage bird use-removal of islands, increasing the steepness of levee slopes, maintenance of relatively high (0.6 m) water levels, and hazing-that greatly reduced the number of waterbirds nesting at large complexes of ponds in the Tulare Basin have been offset by the creation of highly managed compensation wetlands (equipped, for example, with an electric predator-exclusion fence 1.3 m high) that support high numbers and densities of nesting avocets and stilts, though apparently few colonial waterbirds (Davis et al 2005(Davis et al , 2008. Despite these improvements, waterbirds may remain at risk when foraging at canals carrying drainwater with high concentrations of selenium.…”

Bat use of created and natural wetlands

“…But the function of wildlife value is rarely measured because it is more resource intensive than percent surface water or plant cover (NRC 2001, Mitsch and. Several scientific studies have focused on avian , van Rees-Siewert and Dinsmore 1996, Melvin and Webb 1998, Davis et al 2008 and amphibian species composition to assess wetland function. Other studies have investigated invertebrate communities in constructed verses reference wetlands , Balcombe 2005b).…”

“…The function of wildlife value is rarely measured because it is often considered more time consuming and costly than a quick and easy measure of percent surface water or plant cover (Mitsch andWilson 1996, NRC 2001). Several studies have focused on avian , van Rees-Siewert and Dinsmore 1996, Melvin and Webb 1998, Davis et al 2008 and amphibian species composition to assess wetland function (i.e. species diversity).…”