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Waterfowl Breeding Population and Habitat Survey

PURPOSE
The Waterfowl Breeding Population and Habitat Survey was initiated experimentally in 1947 and became operational in 1955. It has been conducted every year since. The primary purpose of the survey is to provide information on spring population size and trajectory for certain North American duck species. These data are used extensively in the annual establishment of hunting regulations in the United States and Canada and provide long-term time series important in researching bird-environment relationships critical to effective conservation planning for waterfowl.

PROCEDURES
Survey procedures and analytical methods for the Waterfowl Breeding Population and Habitat Survey are described in detail by Smith (1995). The U.S. Fish and Wildlife Service and the Canadian Wildlife Service in cooperation with others have conducted an annual survey of breeding waterfowl throughout central Canada, the north-central United States, and Alaska since 1955. The area comprises more than 50 strata delineated according to habitat differences and political boundaries. Since 1990 strata delineated in important duck breeding areas in eastern Canada and the northeast United States have been progressively phased into this long running wildlife survey. Current strata boundaries and the location of transects and segments can be viewed interactively at http://mbirdims.fws.gov/nbii/.

Within strata, ducks are counted by two-person aerial crews while flying fixed-wing aircraft along established transect lines approximately 50 m above ground level. Transects are 400m wide and divided into segments, each roughly 29 km in length. Aerial observers do not count lone hen ducks. Ponds are counted only by the observer, not by the pilot-observer to reduce pilot workload. In prairie and parkland strata, where ground transportation networks and access is good, ground crews survey a sub-sample of aerial segments. Ground counts are used to compute visibility correction factors that adjust the counts of each aerial crew for each species to account for birds not observed from the air.

Ground crews record data in a manner identical to aerial crews, except that ground crews also record lone hens of redheads (Aythya americana), scaups (Aythya marila mariloides and Aythya affinis), ring-necked ducks (Aythya collaris), and ruddy ducks (Oxyura jamaicensis jamaicensis). Unlike the aerial crew, the ground crew also counts all ponds within the entire transect width and records the side of the transect that each pond is observed on. This enables aerial pond data to be compared to the appropriate ground count when computing visibility correction factors. In boreal strata, where ground transportation is difficult, visibility correction factors are determined from a double sample of segments by helicopter. The high cost of helicopter operation currently prohibits extensive double sampling in boreal strata. The total number of birds in each stratum is estimated by the product of the density observed by the aerial crew, the visibility correction factor, and the area of the stratum.

DATABASES
Two databases derived from the Waterfowl Breeding Population and Habitat Survey are available online through the FWS/USGS Migratory Bird Data Center. These are the strata estimates database and the segment-level count database. The strata estimates database includes species- and year-specific estimates and standard errors of absolute waterfowl abundance for individual survey strata. Users querying this database will need to specify the time interval, species, and geographic region of interest.

The segment-level count database records raw count data for the Waterfowl Breeding Population and Habitat Survey at the level of sample segment. The 18-mile long segment is the primary unit on which waterfowl are counted and summarized for this survey. Records in this database include year, strata, transect, and segment identifiers, species, and the number of single drakes, pairs, and mixed sex flocks counted by the aerial survey crew. Users querying this database will need to specify time interval, species, geographic region of interest, as well as 2 additional selection criteria: a) visibility adjusted or raw data, and b) the statistic(s) to report (drakes, pairs, grouped birds, total indicated pairs (TIP), or total indicated birds (TIB)).

If the user specifies visibility corrected data, visibility correction factors derived from a comparison of ground (or helicopter) counts and the counts from fixed-wing aircraft are applied to the raw segment counts.
Total indicated pairs is derived for most species by adding the number of drakes and the number of pairs. The biology of some species (redhead, scaup, ring-necked duck, ruddy duck, swans, and American coot) suggests that assuming that lone drakes represent a breeding pair would lead to an overestimate of breeding pairs. For these species (see excepted species above), TIP equates to the number of pairs observed. Total indicated birds for most species (except species noted above) is TIP times 2 plus the number of birds in mixed sex flocks. For the excepted species noted above, total indicated birds is computed as TIP times 2 plus the number of singles, plus the number of birds in mixed sex flocks.

DOWNLOADABLE FIELD DEFINITIONS

LIMITATIONS
The spatial sampling design and timing of the survey are focused primarily on mallards, an early-nesting species that is important in the annual duck harvest of both the United States and Canada. The survey has known limitations for species which breed in significant densities well beyond the strata boundaries of the survey such as green-winged teal and many sea ducks. Likewise, the timing of the survey, while near optimal for mallards, may be too early for some diving ducks and sea ducks and may result in double counting of birds during migration, or in counting birds prior to reaching their breeding grounds terminus area.

LITERATURE CITED
Smith, G.W. 1995. A critical review of the aerial and ground surveys of breeding waterfowl in North America. Biological Science Report 5, National Biological Service, Washington, D.C. 252pp.

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