California Department of Fish and Wildlife

Population Assessment

Population assessment of Waterfowl is done in the following ways.

Aerial Surveys

Canadian Geese

On the international and national levels, the continental breeding population survey is conducted in the spring by the U.S. Fish and Wildlife Service (USFWS), the Canadian Wildlife Service and others on the primary production (breeding) areas of waterfowl. Breeding population estimates are calculated for the 10 most common North American ducks: mallard, gadwall, American wigeon, green-winged teal, blue-winged teal, northern shoveler, northern pintail, redhead, canvasback, and scaup. These estimates play an important role in establishing annual harvest regulations. Portions of Alaska, Canada, and north-central United States are sampled. The survey consists of both aerial and ground components. The aerial component uses an airplane flying transects at an altitude of 150 feet at about 105 miles per hour, with two observers, one on each side of the aircraft. Every duck seen within an eighth of a mile of the airplane is counted. The species, sex, and social status (paired or unpaired) is determined. Though flying at a low altitude and slow speed by normal aircraft operation, the observers can not see all the birds on the transect. Another set of observers on foot sample a portion of the transects flown by the aerial crew. The difference between what the aerial and ground crews see is used to expand the aerial estimate which minimizes the amount of visibility bias.

On the local level, the California breeding population survey is modeled after the continental breeding survey. Though most of the wintering waterfowl in California breed outside of the state, California still has a significant number that both breed and winter here. CDFW and California Waterfowl Association (CWA) biologists conduct the California survey. Surveyed areas include wetland and agricultural areas in northeastern California, throughout the Central Valley, the Suisun Marsh, and some coastal valleys. CDFW biologists and warden-pilots use a fixed-wing aircraft to fly all of the transects while CWA completes the "ground" portion of the survey using a helicopter. This survey also utilizes a visibility correction factor. For the most part, ducks that only winter in California comprise most of the harvest, but CDFW augments the continental survey assessment with the estimates of California's breeding population for developing hunting regulation recommendations.

A flock of geese

In addition to the breeding area surveys in the spring, the Pacific Flyway states, in cooperation with the USFWS, conduct special fall and midwinter aerial surveys. As in the breeding population surveys, two observers are in the aircraft, but the ground component is not conducted. These surveys sample only the most important migration and wintering areas, and resulting indices describe the relative abundance, trends, and distribution patterns within the Pacific Flyway. Efforts are made to keep sampling efforts (similar observers covering consistent areas over time) constant so that changes in indices will better represent changes in the populations. Fall surveys are used to assess the status of specific goose populations at a time when the geese are still fairly concentrated and not mixed with other populations. The midwinter survey, the longest running population assessment, focuses on all ducks, geese, swans, and coots.

Banding

The CDFW, as well as the USFWS, and private waterfowl conservation groups like CWA, annually capture and band waterfowl. When a band is encountered (typically when a waterfowl hunter takes a bird that has been banded), the date and location are reported to the Bird Banding Laboratory. Analyses of band recoveries have been the primary method used to assess the effect of hunting mortality on waterfowl populations. These analyses are based on the number of bands recovered through time compared with the number of bands originally put on birds. Band recoveries have been, and still are, used to describe migration routes and the affinity between breeding and wintering areas.

Hunter Input

Each year, the USFWS samples a portion requests a portion of the waterfowl hunters who purchased a federal duck stamp to determine keep a diary of their hunting activity and success. An additional sample of hunters are requested to mail in duck wings and goose tail feathers from the birds they take. Following the end of the hunting season, the wings and goose tails are classified by CDFW and other biologists at the "wingbee" to determine the species, age, and sex of each sample. California hosts the wingbee in Anderson, located in northern California. Each state within the Pacific Flyway sends representatives who for five days look at the collected tails and wings. Age is primarily determined by feather shape and wear; sex is determined by color and coloration pattern; and species is determined by coloration pattern and size. An additional number of hunters are selected and asked to keep records of their hunting effort and results.

Results from these two harvest surveys are combined to estimate the size and distribution of harvest among species, and age and sex composition. This information indicates the relative importance of specific species in the harvest in relation to their population status, and the effectiveness of species-specific regulations. For example, mallard populations are doing relatively well , and as a result regulations are liberal (typically a bag limit of seven), and mallards comprise about 25 percent of the California duck harvest. Since pintail populations are well below the long term average, regulations are more restrictive (bag limit of one), so they comprise 9% of the ducks harvested. This information, in combination with population and band recovery analyses, is updated annually and considered during the establishment of hunting regulations.

Careful monitoring and cooperative efforts help all states in the Pacific Flyway make sound regulation recommendations based upon scientific data. Using the scientific methods described, CDFW, other states and the federal government seek to maintain healthy waterfowl populations.