The benefits of crops and field management practices to wintering waterbirds in the Sacramento–San Joaquin River Delta of California

Abstract

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.

A Bioenergetics Approach to Setting Conservation Objectives for Non-Breeding Shorebirds in California’s Central Valley

“…We also excluded alfalfa fields because we considered alfalfa generally too dense to be accessible to most shorebirds over the majority of the growing cycle, and they were not adequately surveyed by Shuford et al (1998). We also excluded the considerable amount of corn grown in the San Joaquin and Tulare basins, which is rarely flooded post-harvest (Fleskes et al 2013;Reiter et al 2015a;Shuford et al 2016). …”

The Relative Importance of Agricultural and Wetland Habitats to Waterbirds in the Sacramento–San Joaquin River Delta of California

“…We randomly selected a first-stage sample of 8 of the 30 primary tracts (three in North Delta, two in Central Delta, and three in South Delta) using generalized random tessellation stratified sampling (Stevens and Olsen 2004) so we could replace tracts, by region, if they were determined inaccessible. We strategically included Staten Island as a third tract in our surveys in the central sub-region because it included a large landscape of flooded habitat and multiple cover types (Shuford et al 2016b), ensuring that we had adequate spatial distribution and sample sizes.…”

“…Recent studies have documented the use of these crops and wetlands by Sandhill Cranes (Antigone canadensis) in broad areas of the Delta (Ivey 2015) and by various waterbird groups (waterfowl [geese, swans, and ducks], cranes, shorebirds, herons, and egrets, etc.) on a large individual Delta island (Shuford et al 2013b(Shuford et al , 2016b. But limited quantitative information exists on broad-scale patterns of crop use by various waterbirds across the entire Delta.…”

Conservation Objectives for Wintering and Breeding Waterbirds in California's Central Valley

“…], triticale [Triticum × Secale], and barley [Hordeum spp. ]) (CVJV 2006;Elphick and Oring 1998;Strum et al 2013;Shuford et al 2016aShuford et al , 2016bSesser et al 2016). Fewer species use dry post-harvest rice and corn fields or other crop types.…”

“…Strategic placement of new roosting sites within crane landscapes will allow birds that use nearby traditional roost sites to easily shift to new roosts and gain access to a larger foraging landscape . Any overall reduction of the quality of crane foraging habitat by flooding corn could be offset by mulching additional areas of corn, because cranes make more extensive use of dry mulched corn than of dry harvest-only corn Shuford et al 2016b). …”