Abstract
Biodiversity loss from agricultural intensification underscores the urgent need for science-based conservation strategies to enhance the value of agro-ecosystems for birds and other wildlife. California’s Central Valley, which has lost over 90% of its historical wetlands and currently is dominated by agriculture, still supports waterbird populations of continental importance. A better understanding of how waterbirds use available habitat is particularly needed in the Sacramento–San Joaquin Delta, an ecosystem under threat. From 2013 to 2015, we studied waterbird habitat associations in the Delta during fall migration and winter by conducting diurnal counts at random locations in key waterbird habitats throughout the Delta. Waterbird use of cover types (agricultural crops and managed wetlands) varied substantially among waterbird groups, by season, and among geographic sub-regions of the Delta. Overall, wetlands were particularly important to waterbirds in fall. In winter, wetlands and flooded rice and corn were important to many waterbird groups, and non-flooded corn and irrigated pasture to geese and cranes. The factors that influenced waterbird abundance and distribution also varied substantially among groups and differed at various geographic scales. In both seasons, most groups had a positive association at the field level with flooded ground and open water, and a negative association with vegetation. Given the great uncertainty in the future extent and pace of habitat loss and degradation in the Delta, prioritizing the conservation actions needed to maintain robust waterbird populations in this region is urgent. For the Delta to retain its importance to waterbirds, a mosaic of wetlands and wildlife-friendly crops that accounts for the value of the surrounding landscape must be maintained. This includes restoring additional wetlands and maintaining corn, rice, alfalfa, and irrigated pasture, and ensuring that a substantial portion of corn and rice is flooded in winter.
Highlights
Increased recognition of the scale of biodiversity loss from agricultural intensification highlights the urgent need for science-based conservation strategies to enhance species richness and abundance of birds and other wildlife in agro-ecosystems
To ensure adequate crop coverage to sample on each tract, we identified tracts with >100 ha each of corn, wheat, and alfalfa, the most widespread “waterbird-friendly” crops in the Delta region
Our study provided data only on overall daytime habitat use patterns but may have obscured consistent diel variation in use patterns for birds such as cranes, which may use different cover types for morning and afternoon foraging periods than for midday loafing (Ivey 2015), and for waterfowl and shorebirds, which may vary by species, daily environmental conditions, and season in the degree to which they forage in the day or night (Miller et al 1985; McNeil et al 1992; Austin et al 2016)
Summary
Increased recognition of the scale of biodiversity loss from agricultural intensification highlights the urgent need for science-based conservation strategies to enhance species richness and abundance of birds and other wildlife in agro-ecosystems. Despite the loss of over 90% of its historic wetlands (Frayer et al 1989; Kempka et al 1991) and the current dominance of agriculture, the Central Valley remains one of the most important regions in the Pacific Flyway of North America for wintering and migratory birds (Shuford et al 1998; Shuford 2014; Fleskes et al 2018). The persistence of wetland-dependent birds reflects the restoration and enhancement of wetlands in recent decades, as well as the birds’ use of certain crops that have offset the loss of the valley’s historically flooded habitats to varying degrees (CVJV 2006). Post-harvest rice (Oryza sativa) and corn (Zea mays) are the most important agricultural habitats in the Sacramento Valley and Sacramento–San Joaquin River Delta (Delta), respectively, for migratory and wintering waterfowl and other waterbirds (CVJV 2006). There is little information on how the location, extent, and juxtaposition of crops and wetlands affects the abundance and distribution of waterbirds at the landscape scale, as has been
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