Goose Population Dynamics in the California Central Valley and Pacific Flyway

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USGS scientists and partners are studying how growing goose populations in the California Central Valley wintering areas are affecting ducks and other waterfowl.

Two geese with white faces stand in a grassy area

Pair of Greater White-fronted Geese at Colusa National Wildlife Refuge.

(Credit: Andrea Mott, USGS Western Ecological Research Center. Public domain.)

Wintering waterfowl habitats in the Central Valley of California are a mixture of seasonally flooded wetlands and seasonally flooded agricultural lands, with a lesser extent of permanently flooded wetlands. All of these habitats, but particularly flooded agriculture and wetlands, provide food for multiple waterfowl species, including several species of geese and ducks. Food resources for waterfowl in the Central Valley are predominately generated through seasonal flooding of various crops, especially rice. Ducks and geese feed on leftover rice grain, along with other plants and invertebrates found in agricultural fields. Food supply is depleted throughout the winter as it is consumed by birds and decomposes in the water, resulting in increased likelihood of food shortages for waterfowl in late winter [1].

Under regional conservation plans, habitat in the California Central Valley is considered available to all types of waterfowl that winter within the region. However, not all waterfowl species use resources in the same way, and it’s possible for one group (e.g., geese) to dominate food resources and increase competition, limiting resources available to other groups (e.g., ducks). Light goose (i.e., Snow geese [Anser caerulescens] and Ross’s Geese [A. rossii], collectively) populations in the Central Valley and the Pacific Flyway are growing [2], and unlike dabbling ducks, geese are able to feed in dry rice fields before they are flooded [1].

Increasing numbers of geese competing with ducks for food resources may be a threat to duck populations in the Central Valley. For instance, duck populations that breed within Suisun Marsh, CA, may be disproportionately affected by food deficiencies and interspecific competition; these birds are dependent on resources in the Central Valley because they do not leave the region like migrating waterfowl and never encounter alternative foraging areas, such as the Southern Oregon- Northeastern California migratory stopover region.

 

Map of goose utilization of rice fields, for four species, showing roosting and feeding locations

Four species of geese utilizing rice agriculture in the Central Valley of California.

(Public domain.)

 

 

Woman holds a white goose wearing a GPS collar

 USGS field biologist Andrea Mott displays a recently marked Lesser Snow Goose.

(Public domain.)

In collaboration with state and federal agencies and nonprofit waterfowl groups, USGS Western Ecological Research Center ecologists are using a multipronged approach to study the population dynamics of geese in the Central Valley and determine how geese may be influencing local duck populations. The six primary project objectives include:

 

1. Telemetry Studies
Snow geese, Ross’s geese, and greater white fronted geese (A. albifrons) captured on the Central Valley wintering grounds have been marked with GPS transmitters to track them in the Central Valley and during migration to breeding areas. Snow geese captured on the Central Valley wintering grounds have been marked with GPS transmitters to track them in the Central Valley and during migration to breeding areas. The goose GPS tracks will be compared with similar GPS data for dabbling ducks to understand overlap in space and habitat use. Ultimately, these data will help the scientists assess competition among geese and ducks and the availability of food resources for ducks. 

2. Remote Identification of Breeding Colonies
In combination with the migratory data provided by the solar powered goose neck collars, USGS is using high-resolution remote sensing imagery of breeding areas to identify and calculate abundance for breeding colonies and estimate the contribution of each breeding colony to the wintering population in the Central Valley. The team will also use this imagery to analyze available area of suitable habitat within waterfowl breeding areas.

Map of North America with migration tracks of four geese species

Migration pathways of four goose species marked with GSM/GPS neck collars, including snow goose, Ross's goose, Tule white-fronted goose, and greater white-fronted goose.

(Public domain.)

White and and brown geese crowded together near a barrier

Lesser Snow Geese are captured using a helicopter to herd them into large pens to await banding.

(Public domain.)

3. Body Condition and Diet During Winter

USGS and collaborators will evaluate body condition and diet of collected geese during fall–winter by analyzing gut contents, diet composition, and lipid content (a measure of body condition). The results will be used to assess relationships between body condition, diet, species, sex, age, mass, and structural body measurements. Data from body condition and diet studies will be used with telemetry GPS data to understand the extent of competition for food between geese and ducks. 

4. Depletion of Waterfowl Food Resources
The team will use remote cameras, goose counts, feces, goose feathers, and other means of estimating food-resource use by geese. The data will be related to food abundance and used to account for relative use by geese and calculate food depletion rates in agricultural fields through time. The results will be used to help understand potential current and future (using population growth projections) food depletion rates in fields and competition for food resources between geese and ducks.

5. Goose Energetic Demand and Identification of Ecological TradeoffsThe researchers will incorporate diet, distribution, and forage depletion information into waterfowl energetics models, such as TRUEMET. TRUEMET is a model used by the Central Valley Habitat Joint Venture to develop regional waterfowl habitat goals. Model results will be used to assess limits to population growth rate of each breeding goose colony and project future contributions of each colony to goose abundance in the Central Valley.

6. Assess Management Options
Data generated by the first five objectives will be used to assess management options for waterfowl in the Pacific Flyway, particularly Suisun Marsh and the Central Valley. USGS will participate in collaborative meetings with conservation partners to discuss management options.

 

Products and Timeline

Goose studies began in 2018 and will continue through 2022, with publications to follow.
 

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Partners

UC Davis

CA Department of Water Resources

CA Department of Fish and Wildlife

US Fish and Wildlife Service

California Waterfowl Association

Ducks Unlimited, Inc.

Central Valley Joint Venture

Ducks Unlimited Canada

Canadian Wildlife Service

Alaska Department of Fish and Game

Washington Department of Fish and Wildlife

North Slope Borough

Idaho Department of Fish and Game

Ministry of Environmental Protection and Natural Resources, Russia

     

    [1] Central Valley Joint Venture, 2006. Central Valley Joint Venture Implementation Plan – Conserving Bird Habitat. U.S. Fish and Wildlife Service, Sacramento, CA.

    [2] U.S. Fish and Wildlife Service. 2017. Waterfowl population status, 2017. U.S. Department of the Interior, Washington, D.C. USA. https://www.fws.gov/migratorybirds/pdf/surveys-and-data/Population-statu...