Sacramento NWR Complex Habitats


The Sacramento NWR Complex contains critically important habitats for a great diversity of wildlife, particularly migratory birds of the Pacific Flyway. Approximately 95% of the historic wetlands, riparian areas, and grasslands in the Central Valley have been destroyed or modified. The Complex maintains nearly 70,000 acres of wetland, upland and riparian habitats.

  • Seasonal Wetlands

    Seasonal wetlands make up the majority of the refuges' wetland habitat.  They are flooded from fall through spring, and then are dry from late spring through summer.  When ponds are drawn down in the spring, seed-producing plants germinate and grow on the moist pond bottoms. The seeds and invertebrates these ponds produce become available to waterfowl and other wetland species when they are flooded in the fall. Seasonal wetlands provide important resting and feeding habitat for waterfowl, shorebirds, egrets, herons, raptors and other wetland-dependent wildlife from fall to spring. Common plants include cattail, hardstem bulrush, alkali bulrush, and swamp timothy.

  • Irrigated Seasonal Wetlands

    Some seasonal wetlands (described above) receive an irrigation during the spring or summer months in order to increase seed and vegetative production.  Irrigations can last for a few days or over a month, depending on weather conditions and plant response.  Shorter irrigations can enhance smaller stature plants, like swamp timothy, while longer irrigations can bring taller plants, such as watergrass and smartweed, to full maturation.  Other plants that also respond with vigorous growth include sprangletop, spikerush, Bermuda grass, and joint grass.  Because of the high seed production, irrigated seasonal wetlands have the highest waterfowl use, but tend to have decreased use by shorebirds due to the taller and denser plant structure.

  • Permanent/Semi-Permanent Wetlands

    Permanent wetlands are flooded year-round and provide a water source that is valuable to resident wildlife, especially during the summer when most of the seasonal wetlands are dry. Semi-permanent wetlands are flooded from fall through summer, and are dry for a short window in late summer so that plant germination and nutrient recycling can occur.  During the summer, when flooded habitat is scarce, these ponds provide nesting areas for resident waterfowl and other wildlife. During the fall and winter, they add to the important resting and feeding areas on the refuge. Characteristic plants include cattail, hardstem bulrush, burhead and sago pondweed.

  • Riparian Areas

    Riparian areas tend to grow in linear areas along the edges of rivers, creeks, and waterways and can characterized by the thick growth of trees and shrubs.  This scarce waterside habitat supports a great diversity of wildlife. It is heavily used by neo-tropical migrant bird species such as the yellow-billed cuckoo, black-headed grosbeak, spotted towhee and dozens of songbird species. It also provides important breeding habitat for colonial nesting egrets and herons, as well and raptors, such as hawks, eagles and owls. Cottonwoods, valley oaks, sycamores, willows, box elders, elderberry, and wild rose are common plants found in riparian areas.

  • Uplands/Grasslands

    Upland areas include a mixture of grasslands and vernal pool/alkali meadow habitats. Many of the grassland areas have been restored to native grasses and wildflowers. In areas with more alkaline (salty) soils, rainwater tends to naturally puddle in depressions and create what are referred to as "vernal pools".  Salt-tolerant native plants grow well in these alkaline areas.  In the spring, these areas produce a carpet of protein-rich grass shoots and vernal pools are often filled with invertebrates, providing an important food source for waterfowl and shorebirds that are preparing for spring migration.  During the spring and summer months, they provide nesting habitat for ducks, pheasants, meadowlarks, burrowing owls, bitterns, and northern harriers. In the winter and spring, annual grasses provide food for geese, coots, and wigeon. They also support significant numbers of insects, rodents, and reptiles which in turn are important forage items for raptors and birds. Goldfields, downingia, and popcorn flowers bloom brilliantly on the edges of the vernal pools in late spring. Other plants include: saltgrass, saltbush, and annual grasses.

  • Habitat Maps

    In late spring of each year, a Habitat Management Plan is written for each Refuge. To see the most recent Habitat Management Maps, click on the links below:

    - Sacramento NWR Habitat Map 
    - Delevan NWR Habitat Map 
    - Colusa NWR Habitat Map 
    - Sutter NWR Habitat Map 
    - Sacramento River NWR Habitat Maps (large file)
    - North Central Valley WMA - Llano Seco Unit Habitat Map 
    - Butte Sink WMA - Butte Sink Unit Habitat Map