Abstract
Author(s): Dybala, Kristen E.; Reiter, Matthew E.; Hickey, Catherine M.; Shuford, W. David; Strum, Khara M.; Yarris, Gregory S. | Abstract: An extensive network of managed wetlands and flooded agriculture provides habitat for migrating and wintering shorebirds in California’s Central Valley. Yet with over 90% of historical wetlands in the region lost, Central Valley shorebird populations are likely diminished and limited by available habitat. To identify the timing and magnitude of any habitat limitations during the non-breeding season, we developed a bioenergetics model that examined whether currently available shorebird foraging habitat is sufficient to meet the daily energy requirements of the shorebird community, at either the baseline population size surveyed from 1992 to 1995 or double this size, which we defined as our long-term (100-year) population objectives. Using recent estimates of the extent of managed wetlands and flooded agriculture, satellite imagery of surface water, energy content of benthic invertebrates, and shorebird metabolic rates, we estimated that shorebird foraging habitat in the Central Valley is currently limited during the fall. If the population sizes were doubled, we estimated substantial energy shortfalls in the fall (late July–September) and spring (mid-March–April) totaling 4.02 billion kJ (95% CI: 2.23–5.83) and 7.79 billion kJ (2.00–14.14), respectively. We then estimated long-term habitat objectives as the minimum additional shorebird foraging habitat required to eliminate these energy shortfalls; the corresponding short-term (10-year) habitat objectives are to maintain an additional 2,160 ha (5,337 ac) of shallow (l10 cm) open water area in the fall and 4,692 ha (11,594 ac) in the spring. Because the Central Valley is one of the most important regions in the Pacific Flyway for migrating and wintering shorebirds, we expect that achieving these habitat objectives will benefit shorebirds well beyond the Central Valley. Our bioenergetics approach provides a transparent, repeatable process for identifying the timing and magnitude of habitat limitations as well as the most efficient strategies for achieving conservation objectives.
Highlights
The Central Valley of California is one of the most important regions for migrating and wintering shorebirds (Order: Charadriiformes; Sub-Orders: Scolopaci, Charadrii) in western North America with at least half a million birds using the region each year (Shuford et al 1998)
The observed size of the baseline shorebird community increased between August and April during the 1992-1995 baseline surveys (Figure 2A; Shuford et al 1998), peaking during spring migration when shorebirds are concentrated in the Central Valley
The long-term (100year) population objectives, based on doubling these observed population sizes, increase linearly from the assumed starting point of 50,000 birds on 1 July (CVJV 2006) to 269,143 by 15 August, reach a peak of 666,739 by 15 April, and decline sharply back to 50,000 by 15 May (Figure 2A). These objectives are very similar to the objectives previously adopted in the Southern Pacific Shorebird Conservation Plan and the 2006 Central Valley Joint Venture Implementation Plan, which include 200,000 in the fall, 400,000 in the winter, and 600,000 in the spring (Hickey et al 2003; CVJV 2006), but they provide specific numbers for each day of the nonbreeding season
Summary
The Central Valley of California is one of the most important regions for migrating and wintering shorebirds (Order: Charadriiformes; Sub-Orders: Scolopaci, Charadrii) in western North America with at least half a million birds using the region each year (Shuford et al 1998). Central Valley shorebird populations were likely once much larger, and may be limited by the availability of suitable foraging habitat (Page and Gill 1994; Shuford et al 1998). An extensive network of restored and managed wetlands and post-harvest flooded rice, corn, and other crops currently provide substantial habitat for non-breeding shorebirds in the Central Valley (Fleskes et al 2012; Strum et al 2013; Reiter et al 2015b). As the availability and cost of water in the Central Valley varies with changing supply and demand, drought conditions, and the effects of climate change (Hanak and Lund 2012), the ability to supply water where and when it is most needed will maximize the benefits of this limited resource to non-breeding shorebirds
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