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The Grasslands Ecological Area is the largest contiguous wetland complex in California's Central Valley and is a stronghold for hundreds of thousands of waterbirds. Primarily managed for waterfowl habitat and forage production, landowners of these privately owned seasonal wetlands in the Grassland Ecological Area typically flood the wetlands in the fall and dewater them the following spring in February and March. These wetlands support large populations of nonbreeding shorebirds and other waterbirds in winter. When the number of migratory shorebirds using the region peaks in mid-April, landowners have already dewatered most wetlands. The mismatch in the timing of available habitat and the habitat needs of migrating shorebirds contributes to the observed deficit of shorebird habitat in the Central Valley in spring. Working with private landowners, we developed and tested a wetland management practice designed to increase the amount of shallow-water habitat available to shorebirds in April by delaying the drawdown and reducing water levels more slowly (gradual drawdown) relative to the traditional management practice. On average, we found that wetlands managed with gradual drawdown provided over twice as much shorebird habitat, contributing up to 26% of the overall shorebird habitat objective for the Central Valley. Wetlands managed with gradual drawdown supported up to 21 times more migratory shorebirds during peak migration and a greater number of shorebird species than traditionally managed wetlands. Our results demonstrate the potential of working with private landowners to implement small changes in wetland management that can have a large impact in meeting regional conservation objectives for migratory shorebirds.

Many shorebirds (Order: Charadriiformes; Family: Charadriidae, Recurvirostridae, Scolopacidae, Haematopodidae, Jacanidae) are highly migratory, traversing thousands of kilometers between high latitude breeding and low latitude nonbreeding sites. In doing so, they are dependent on networks of coastal and interior wetland ecosystems. To aid in the effective conservation and management of their populations, and to assess the impact of threats facing shorebirds, standardized data on shorebird abundance are needed from multiple sites representing a gradient of conditions across the hemisphere. Such data would provide insight on whether fluctuations at one location represent real changes in abundance because of some localized threat, or whether other factors acting across broader scales such as the redistribution of predators, are responsible. We designed the Migratory Shorebird Project (MSP), now implemented in 11 countries along the Pacific Coast of the Americas, to characterize spatial and temporal variation in shorebird abundance, to understand which factors (habitat, threats) most influence their populations across the flyway, and to increase capacity for integrated research, monitoring, and conservation. We used bird inventory data from historical surveys and spatial data on habitat distribution along with a set of hypotheses about important threats to guide the design of the project and to identify data requirements to test hypotheses. We counted birds one time per year at 84 nonbreeding sites (~1400 sampling units) between 15 November and 15 February, when shorebirds were relatively stationary. In each of the first three annual counts from 2013/14 to 2015/16, the Migratory Shorebird Project counted ~1M shorebirds representing 44 species, including five species for which > 20% of the estimated biogeographic population was recorded annually, and nine additional species with > 5% recorded annually. The magnitude of variability in estimates of shorebird abundance was inversely correlated with survey effort with the most uncertainty, and lowest survey effort, in the South Temperate region followed by the Neotropical region (southern Mexico to northern Peru) and then the North Temperate region. Evaluation of variance highlighted both among-site and among-unit ("units" are nested within sites) variation in bird abundance and cover types as well as threats such as potential disturbance and predator abundance. Overall, shorebird density was significantly, and positively, associated with the area (ha) of intertidal mudflats, beaches, and aquaculture. Survey units with intermediate levels of bare ground and flooding had the highest shorebird density. As for threats, we found, contrary to our hypothesis, that shorebird abundance was significantly, and positively, associated, with the density of Peregrine Falcons (Falco peregrinus); however we found no relationship between shorebird abundance and the amount of urban development, our index to potential human disturbance, in the surrounding landscape. The Migratory Shorebird Project is providing an essential data foundation and network for increased knowledge of the factors affecting shorebirds across the Pacific Coast of the Americas and identifying what and where conservation actions could have the greatest impact.

There are many benefits of agricultural landscapes for wildlife. In California's Central Valley, post-harvest flooding of rice fields increases the decomposition of rice stubble and provides habitat for over 50 species of waterbirds. These fields are also flooded during planting, providing habitat for spring migrants and locally breeding birds. Because California has lost over 90% of its historic wetlands, flooded rice is critical wildlife habitat, providing 80% of the total flooded habitat in the Sacramento Valley. Flooding rice fields, however, contributes to greenhouse gas (GHG) emissions. Several rice field management practices may reduce methane emissions including reduced flooding in winter, removal of rice straw after harvest (baling), and drill seeding during planting. During the winters of 2011–2012 and 2012–2013, we compared waterbird use in four combinations of post-harvest practices: baled/flooded, baled/non-flooded, non-baled/flooded, and nonbaled/non-flooded. We found significantly higher dabbling duck and shorebird densities in the non-baled/flooded practice compared to the other three practices. During the spring of 2012 and 2013, we compared waterbird use of drill-seeded fields (reduced GHG) with flooded fly-on seeded fields (status quo GHG). We found no significant differences in mean density between the two seeding practices for waterbirds. Our study found evidence that some post-harvest practices (reduced winter flooding, baling) that reduce GHG emissions from rice also reduce use by waterbirds. While reducing GHG is globally necessary to minimizing the impacts of climate change, doing so in an area of hemispheric importance for waterbirds should be done with caution.

Wetland loss and degradation have been extensive across the world, especially in California's Central Valley where over 90% of the natural wetlands have been converted to agricultural and urban uses. In the Central Valley today, a much smaller network of managed wetlands and flooded agricultural fields supports almost five million waterfowl and half a million shorebirds. Over 50% of waterbird habitat in the Central Valley is provided by flooded agricultural land, primarily rice (Oryza sativa). Each year non-breeding waterbird habitat decreases in the late winter as flooded agricultural fields are drained after waterfowl hunting season in late-January to prepare for the next crop. This study evaluated a practice called 'variable drawdown' that involves delaying the removal of water from rice fields by 1, 2, and 3 weeks to extend the availability of flooded habitat later into February and March. We studied waterbird response to variable drawdown in 2012 and 2013 at twenty rice farms throughout the northern half of the Central Valley. The staggered drawdown created a mosaic of water depths throughout the six-week study period. The 3-week delay in drawdown supported more dabbling ducks than earlier drawdowns in the first half of the study and more shorebirds and long-legged wading birds during the second half of the study. The timing of highest use of each drawdown treatment differed for each waterbird guild; dabbling ducks, geese and swans benefited at the beginning, then long-legged wading birds, followed by shorebirds. Despite the presence of appropriate water depths for shorebirds across the treatments during the entire study period, shorebird densities were highest near the end of the study when the 3-week-delayed drawdown was providing the majority of the habitat on the landscape. This suggests that shorebirds may have concentrated in our study fields due to decreasing availability of shallow water habitat elsewhere. The practice of variable drawdown successfully extended the availability of waterbird habitat provided by post-harvest flooded rice fields later into winter.

Agricultural intensification has been a major factor in the loss of global biodiversity. Still, agricultural landscapes provide important habitat for many bird species, particularly in the Central Valley of California, USA, where >90% of the natural wildlife habitat has been lost. As wildlife professionals increasingly work with agricultural producers to promote ‘wildlife-friendly’ farming, it is important to understand the relative value of specific crops and field management practices to birds. The value to wintering waterbirds of seven treatments (crop and management practice combinations) across two crops (corn and winter wheat) was assessed at Staten Island in the Sacramento–San Joaquin River Delta of the Central Valley. Significant variation in the relative abundance of waterbirds was found among management practices, and post-harvest flooding and chopping and rolling (mulching) of corn were most beneficial to waterbirds. As expected, most waterbirds were common in flooded treatments, but geese, cranes and long-legged waders also were numerous in some dry treatments. Our data suggest that a greater waterbird species richness and abundance can be achieved by maintaining a mosaic of dry and flooded crop types, varying water depths and continuing the chop-and-roll practice for flooded corn. The observed benefits of particular crops and field management practices in this study should aid in the development of incentive-based programs to improve the habitat value of other working lands both within, and outside, the Delta.

Conservation of grassland vertebrates requires a mechanistic understanding of the effects of landscape heterogeneity on habitat selection and demographic performance. Our goal was to investigate the effects of rangeland management on resource selection and nest survival of upland sandpipers (Bartramia longicauda). We conducted our project at Konza Prairie, a Long-Term Ecological Research site. The station has 60 experimental units with replicated grazing and fire treatments that create a heterogeneous landscape of different habitat patches. We radio-tracked sandpipers for two breeding seasons (2003–2004, n = 37 birds) and monitored sandpiper nests for eight seasons (2001–2008, n = 246 nests). We used resource utilization functions to examine resource selection with respect to five landscape features. Home ranges of sandpipers were large in contiguous prairie ( $$\bar{x} = 8.4\;{\text{km}}^{ 2}$$ ) and explain area-sensitive occurrence in fragmented prairie. Upland sandpipers selected grazed and burned sites with short vegetation within their home range. In contrast, nest site selection was influenced by fire frequency and birds selected infrequently burned sites with greater vegetative structure. Settlement decisions affected fitness because nest survival was low in burned and grazed sites (0.068), but higher in unburned and ungrazed sites (0.201–0.247). Our results raise concerns for conservation because private rangelands managed for livestock production are often homogeneous landscapes with heavy grazing and frequent fires. Rotational grazing and fire could be used to restore heterogeneity to grasslands but the duration of rotation, patch size, and optimal configuration require further investigation.

https://doi.org/10.15447/sfews.2017v15iss1art2An 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 (

Author(s): Strum, Khara M.; Dybala, Kristen E.; Iglecia, Monica N.; Shuford, W. David | Abstract: The Central Valley of California provides important breeding habitat to numerous species of wetland-dependent birds, despite the loss of over 90% of naturally occurring wetlands. A majority of shorebirds breeding in this region rely on shallow-flooded habitat adjacent to sparsely vegetated uplands as provided by rice (Oryza sativa), managed wetlands, and other habitats. We estimated the current extent of potential breeding shorebird habitat provided by rice and managed permanent and semi-permanent wetlands in each of four major planning regions of the Central Valley, and estimated the average breeding densities and current population sizes of two species of shorebirds: the Black-Necked Stilt (Himantopus mexicanus) and American Avocet (Recurvirostra americana). Using a population status framework based on principles of conservation biology, we estimated that stilt populations are small (l10,000 individuals) or very small (l1,000 individuals) in three of the four planning regions, and avocet populations are small or very small in all four planning regions. We then used the framework to define long-term (100-year) population objectives for stilts, avocets, and a third species, Killdeer (Charadrius vociferous), designed to meet our long-term conservation goal of supporting self-sustaining, genetically robust, and resilient populations of breeding shorebirds in the Central Valley. We also estimated the long-term species’ density and wetland habitat objectives necessary to achieve the population objectives for all three species. The corresponding short-term (10-year) conservation objectives are to restore semi-permanent wetlands to provide an additional 11,537 ha (28,508 ac) of habitat for breeding shorebirds (by planning region: 2,842 ha in Sacramento, 2,897 ha in Yolo–Delta, 2,943 ha in San Joaquin, and 2,855 ha in Tulare), and to enhance existing habitat to support density objectives. Our approach provides a transparent, repeatable process for defining science-based conservation objectives for breeding shorebirds and their habitats in the Central Valley, which can help unite stakeholders around common goals and motivate conservation actions.

A principal goal of conservation efforts for threatened and endangered taxa is maintenance of genetic diversity. Modern and historic processes that limit population size can contribute to a loss of genetic variation that can reduce future adaptability of a species. Buff-breasted Sandpipers (Calidris subruficollis) are a Neotropical migratory shorebird that experienced rapid, large-scale declines in population numbers (population bottleneck) due to intensive market hunting at the turn of the 20th century. Market hunting ended shortly after the passage of the Migratory Bird Treaty Act in 1918, but subsequent population losses have occurred due to continued anthropogenic disturbances throughout the species’ migratory range. To assess the impact of population declines on the genetic variation of Buff-breasted Sandpipers, we surveyed two mitochondrial DNA (mtDNA) markers, the control region and cytochrome b, from 209 museum specimens collected between 1874 and 1983 and 460 modern samples collected between 1993 and 2009. Measures of mtDNA variation did not change significantly among individuals sampled before and after the ban on market hunting, nor among four temporal groups (Pre-Act, Early Post-Act, Late Post-Act, and Modern; trend analysis: χ 2 = 0.171, P = 0.679). Similarly, we did not observe loss of common haplotypes, implying that there was no substantial reduction in unique matrilineal units during our 135-year study period. Using Bayesian Skyline reconstruction of temporal changes in effective population size of females (N ef), we concluded that N ef has been stable for the past century. Results of resampling suggest that diversity estimators can be imprecise and we emphasize the importance of a well-rounded analytical approach to addressing conservation genetic hypotheses. Considering all of the evidence it appears that genetic variation and N ef were stable despite the pressures of market hunting early in the 20th century and habitat loss and degradation in the latter half of the 20th century. Conservation efforts should continue to focus on maintaining the population size of Buff-breasted Sandpipers to avoid reaching a threshold where genetic variability is lost.

Rice agriculture provides habitat for waterbirds in California's Sacramento Valley, a region that has lost over 90% of natural wetlands. Developed as an agronomic practice, winter-flooding of rice fields also provides habitat for waterbirds but alternatives are needed with predicted declines in water availability. During the winters of 2009–2010 and 2010–2011, we compared waterbird density and water depths of Sacramento Valley rice fields in four post-harvest management treatments that varied in the amount of water used: maintenance flooding, one-time flooding, non-flooded with boards left in water control structures, and non-flooded with boards removed from water control structures. Densities of waterbirds were higher in the flooded treatments compared to non-flooded treatments. One-time flooding provided the most suitable water depths for shorebirds and long-legged waders while maintenance flooding provided the most suitable water depths for dabbling ducks. Our results confirm that the practice of winter-flooding rice fields provides waterbird habitat. However, increased habitat value and potentially less water use could be achieved using a combination of traditional and alternative flooding practices.

Range-wide monitoring of shorebirds (Aves: Charadriiformes) suggests that many species are declining. For most species, it is unknown whether distinct population units exist, which makes management and conservation difficult. One shorebird of conservation concern, the Buff-breasted Sandpiper (Tryngites subruficollis), is a New World migrant that breeds at Arctic latitudes in North America and Russia and winters in southeastern South America. We conducted a molecular survey of samples representing each of three migratory regions (breeding, migration, and wintering) using nine polymorphic microsatellite loci and 1.5 kb of highly variable mitochondrial DNA (mtDNA) from the cytochrome b gene and mtDNA control region. We analyzed contemporary population structure, demographic trends, and phylogeographic patterns. Overall, microsatellite and mtDNA analyses revealed that Buff-breasted Sandpipers are panmictic both regionally and at a global scale, with no signal of a recent genetic bottleneck. The mtDN...

Migratory shorebirds frequently forage and roost in agricultural habitats, where they may be exposed to cholinesterase-inhibiting pesticides. Exposure to organophosphorus and carbamate compounds, common anti-cholinesterases, can cause sublethal effects, even death. To evaluate exposure of migratory shorebirds to organophosphorus and carbamates, we sampled birds stopping over during migration in North America and wintering in South America. We compared plasma Cholinesterase activities and body masses of individuals captured at sites with no known sources of organophosphorus or carbamates to those captured in agricultural areas where agrochemicals were recommended for control of crop pests. In South America, plasma acetylcholinesterase and butyrylcholinesterase activity in Buff-breasted Sandpipers was lower at agricultural sites than at reference sites, indicating exposure to organophosphorus and carbamates. Results of plasma Cholinesterase reactivation assays and foot-wash analyses were inconclusive. A meta-analysis of six species revealed no widespread effect of agricultural chemicals on Cholinesterase activity. However, four of six species were negative for acetylcholinesterase and one of six for butyrylcholinesterase, indicating negative effects of pesticides on Cholinesterase activity in a subset of shorebirds. Exposure to Cholinesterase inhibitors can decrease body mass, but comparisons between treatments and hemispheres suggest that agrochemicals did not affect migratory shorebirds' body mass. Our study, one of the first to estimate of shorebirds' exposure to cholinesterase-inhibiting pesticides, suggests that shorebirds are being exposed to cholinesterase-inhibiting pesticides at specific sites in the winter range but not at migratory stopover sites. Future research should examine potential behavioral effects of exposure and identify other potential sites and levels of exposure. Instituto de Recursos Biológicos Fil: Strum, Khara M. Kansas State University. Division of Biology; Estados Unidos Fil: Hooper, Michael J. Texas Tech University. Institute of Environmental and Human Health; Estados Unidos Fil: Johnson, Kevin A. Southern Illinois University. Department of Chemistry and Environmental Sciences; Estados Unidos Fil: Lanctot, Richard B. United State Fish and Wildlife Service. Migratory Bird Management; Estados Unidos Fil: Zaccagnini, Maria Elena. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Recursos Biológicos; Argentina Fil: Sandercock, Brett K. Kansas State University. Division of Biology; Estados Unidos