Non-Tidal Wetlands & Waters – Waterbirds
What are Non-Tidal Wetlands and Waters?
Updated: 20250808
Non-Tidal Wetlands and Waters is broad and encompasses all diked baylands including diked wetlands, managed ponds, and salt production ponds. These non-tidal habitats replicate historic conditions that have mostly disappeared: salt pannes and pools, seasonal wetlands, and managed marsh. Together, these areas provide a range of water depth, salinity, and other features to support diverse wildlife communities including waterfowl and breeding shorebirds and provide recreational and wildlife viewing along the bay shore.
The non-tidal wetlands and waters habitat indicators are mixed, with managed ponds providing good habitat for some (wintering dabbling ducks) but not for others (breeding waterbirds). Non-tidal wetlands and waters in Suisun are struggling to provide quality habitat for the breeding waterfowl indicator.
Thousands of dabbling ducks come to SF Bay each year to spend the winter. They feed on the water’s surface or in shallow water gaining the calories needed to fuel their journey northward and given them a strong start to the breeding season. These six species of dabblers (Family Anatidae) were the most abundant in SF Bay: American Wigeon (Mareca americana), Gadwall (M. strepera), American Green-winged Teal (Anas crecca), Mallard (A. platyrhynchos), Northern Pintail (A. acuta), and Northern Shoveler (Spatula clypeata) that winter in the managed ponds in the north and south bay.
Many Mallard (Anas platyrhynchos) and Gadwall (Mareca strepera) remain in SF Bay to breed. They were selected as breeding indicators of non-tidal wetlands because they are the two most common nesting dabbling duck species in California that breed baywide, the majority in Suisun Marsh upland and non-tidal wetlands. These dabbling duck species require upland edge habitats for nesting, and adjacent wetlands to raise young.
Mallard (Anas platyrhynchos) and Gadwall (Mareca strepera) were selected as breeding indicators of non-tidal wetlands because they are the two most common nesting dabbling duck species in California that breed baywide, the majority in Suisun Marsh upland and non-tidal wetlands. These dabbling duck species require upland edge habitats for nesting, and adjacent wetlands to raise young.
American Avocet, Black-necked Stilt, and Forster’s Terns are colonial nesting waterbirds that use the managed island ponds for breeding, primarily on constructed islands in the South Bay Salt Pond complex.
Non-Tidal Wetlands and Waters Indicator Species Groups
Green-winged Teal
American Wigeon
Northern Pintail
Northern Shoveler
Mallard
Gadwall
Mallard
Gadwall
American Avocet
Black-necked Stilt
Forster’s Tern
Non-Tidal Wetlands and Waters Indicator Species Groups
Green-winged Teal
American Wigeon
Northern Pintail
Northern Shoveler
Mallard
Gadwall
Mallard
Gadwall
American Avocet
Black-necked Stilt
Forster’s Tern
Wintering Dabbling Ducks
Dabbling ducks are increasing overall, indicating that non-tidal wetlands and waters are providing quality habitat.
Dabbling duck abundance from the Midwinter Waterfowl Survey. Counts were summarized from the North Bay Open Bay, North Bay Salt Ponds, Central Bay Open Bay, Shoreline, South Bay Open Bay, and South Bay Salt Ponds.
Over the past three decades, the total number of wintering dabbling ducks across the entire bay increased. This trend was primarily due to significant rises in the populations of northern shoveler and American wigeon. American green-winged teal and gadwall also saw notable increases, though they are still among the least common dabbling ducks in the San Francisco Bay.
However, the populations of northern pintail and mallard did not change significantly. Regional data show that these increases in dabbling ducks were observed in the former salt ponds of the North and South Bay, as well as in the North Bay’s subtidal habitats. These long-term increases in some dabbling duck species might be a positive sign, reflecting their response to early tidal restoration efforts and the careful management of the remaining former salt ponds in both the North and South Bays.
North Bay and South Bay managed ponds generally provide good quality habitat for wintering dabbling ducks.
Long-term trends of dabbling duck abundances for North Bay (left) and South Bay (right) managed ponds.
Trends by Species
Loess-smoothed long-term trends of dabbling duck species in San Francisco Bay from the Midwinter Waterfowl Survey conducted in January from 1989 to 2024. Counts were summarized from the North Bay Open Bay, North Bay Salt Ponds, Central Bay Open Bay, Shoreline, South Bay Open Bay and South Bay Salt Ponds and were adjusted for differences in survey effort among years.
Subregional Indicators for Managed Wetlands
Breeding Dabbling Ducks in Suisun Marsh
What is Suisun Marsh?
The non-tidal wetlands and waters in Suisun are struggling to provide quality habitat for a key indicator species, breeding dabbling ducks.
Mallard
Gadwall
Mallard nesting has declined at every scale, with the largest decline across the whole time period.
Gadwall nesting in Suisun show a relatively stable breeding population across the time series, and a slight, but not significant increase in the recent period.
The Suisun indicator focuses on Grizzly Island Wildlife Area which provides 1,600 ha. of managed uplands and seasonal wetlands that support breeding dabbling ducks. These upland habitats are dominated by mid-height grasses, taller grasses, and forbs.
Breeding waterfowl in Suisun…
California’s breeding waterfowl populations have significantly declined over the past three decades, now standing at 71% below the USFWS Central Valley Joint Venture’s population objective. [Text placeholder for SFBJV pop objective percentage] The mallard breeding population, in particular, has seen a consistent decline during this period.
Although Suisun Marsh is vital for California’s waterfowl, hosting some of the state’s highest duck nesting densities, its mallard nesting populations (the most numerous duck nesting species in California) have also decreased. In contrast, gadwall nesting populations have been more stable, but their overall nesting densities across the state remain lower.
Breeding Waterbirds in the South Bay
Photo by Chris Benton
Breeding waterbirds in South San Francisco Bay…
Breeding Waterbirds in the South Bay Multi-Species Indicator
American Avocet and Black-necked Stilt breeding has decreased in South Bay managed ponds, though was relatively stable for Forster’s Tern.
Nesting waterbird trends were mixed. Two species declined and one had no statistically significant trend in nest abundance of over the 20–year study period in South San Francisco managed ponds.
- American Avocet nest abundance declined and leveled off at low numbers.
- Black-necked Stilt nest abundance declined sharply then leveled off at low numbers.
- Forster’s Tern nest abundance varied with no significant trend over the 20-year period despite a recent increase.
American Avocet and Black-necked Stilt populations in the SF Bay Estuary are declining due to the loss of their preferred island nesting habitats within managed wetlands. While Forster’s Tern populations, one of the most abundant breeding birds in the San Francisco Bay/Estuary and who also nest on these islands, have varied but have recently increased. Efforts to build new island nesting sites and use social attraction methods, like decoys and calls, have helped boost local nesting populations in managed wetlands.
South Bay Salt Pond Restoration Project
Habitat Popup 1
Non-Tidal Wetlands and Waters Habitat…