Wildlife Monographs
Determinants of Breeding Distributions of Ducks
Methods
Survey Design
Each year ducks and ponds are counted in the major North American breeding areas. The survey design and data gathering techniques were described in detail by D. C. Bowden (Review and evaluation of May waterfowl breeding ground survey, unpubl. rep., U.S. Fish and Wildl. Serv., Patuxent, Laurel, Md., 1973), Anonymous (1977), and Martin et al. (1979).
The region from which samples are drawn consists of about 3.03 million km2 (1.17 million sq miles) in the north-central United States, the prairie provinces and Northwest Territories of Canada, and Alaska (Fig. 1). About 78-84% of North American mallards breed within the surveyed area (Pospahala et al. 1974, R. S. Pospahala, unpubl. memorandum 1985). Because the other 9 species have breeding ranges more restricted to that area (Bellrose 1980), even greater percentages of their continental populations probably nest in the surveyed area.
The region is divided into 49 strata (Table 1), ranging in size from 1,036 to 424,400 km2 (400-163,861 sq miles). Stratification is based both on political boundaries and on geographical differences in duck densities (Stewart et al. 1958).
Table 1. Strata used in May waterfowl surveys: name, area, number of transects, and area sampled, 1955-81.
| Stratum | Name | Area (Sq. miles) |
No. of Tran- sectsa |
Area Sampled (Sq. miles) |
| 1 | Kenai-Susitna | 2200 | 6 | 40 |
| 2 | Nelchina | 3900 | 10 | 52 |
| 3 | Tanana-Kuskokwim | 9300 | 18 | 132 |
| 4 | Yukon Flats | 10800 | 12 | 80 |
| 5 | Innoko River | 3400 | 7 | 44 |
| 6 | Koyukuk River | 4100 | 10 | 80 |
| 7 | Copper River Delta | 400 | 1 | 20 |
| 8 | Bristol Bay | 9900 | 11 | 92 |
| 9 | Yukon Delta | 26600 | 8 | 260 |
| 10 | Seward Pennisula | 3850 | 4 | 24 |
| 11 | Kotzebue | 5350 | 7 | 48 |
| 12 | Old Crow Flats | 1970 | 3 | 36 |
| 13 | Mackenzie River Delta | 4935 | 4 | 36 |
| 14 | Northwest Territories Forest Tundra | 79217 | 8 | 364 |
| 15 | Northwest Territories Forest Tundra | 50462 | 2 | 108 |
| 16 | Slave River Parklands | 57821 | 4 | 94.5 |
| 17 | Northwest Territories Closed Forest and Forest Tundra | 69033 | 5 | 297 |
| 18 | Northwest Territories Pre-Cambrian Edge | 11733 | 3 | 27 |
| 19 | North Alberta Parklands and Closed Forest | 163861 | 8 | 688.5 |
| 20 | Athabasca River Delta | 1625 | 4 | 31.5 |
| 21 | Northern Saskatchewan Mixed Forest | 44922 | 11 | 382.5 |
| 22 | Northern Saskatchewan Mixed Forest | 20278 | 6 | 166.5 |
| 23 | Northern Saskatchewan Pre-Cambrian Shield and Mixed Forest | 68320 | 6 | 297 |
| 24 | Manitoba Pre-Cambrian Shield, Muskeg, and Mixed Forest | 83794 | 8 | 490.5 |
| 25 | Saskatchewan River Delta | 6816 | 6 | 117 |
| 26 | Alberta Parklands | 26448 | 6 | 265.5 |
| 27 | Alberta Prairie | 11724 | 3 | 144 |
| 28 | Alberta Prairie | 12890 | 3 | 135 |
| 29 | Alberta Prairie | 13235 | 4 | 171 |
| 30 | Southern Saskatchewan Mixed Forest (west) | 18570 | 4 | 162 |
| 31 | Southern Saskatchewan Mixed Forest (east) | 21086 | 5 | 135 |
| 32 | Saskatchewan Prairie | 37911 | 14 | 571.5 |
| 33 | Cypress Hills | 11345 | 6 | 90 |
| 34 | Saskatchewan Parklands | 13164 | 5 | 175.5 |
| 35 | Saskatchewan Parklands | 9044 | 6 | 126 |
| 36 | Manitoba Interlake Region | 5500 | 3 | 58.5 |
| 37 | Manitoba Interlake Region | 16485 | 4 | 130.5 |
| 38 | Manitoba Parklands | 5655 | 3 | 54 |
| 39 | Manitoba Parklands | 6552 | 5 | 121.5 |
| 40 | Manitoba Parklands | 4536 | 4 | 67.5 |
| 41 | Montana North River | 32902 | 7 | 504 |
| 42 | Montana South River | 40755 | 7 | 364.5 |
| 43 | North Dakota West River | 19835 | 5 | 175.5 |
| 44 | South Dakota West River | 27299 | 5 | 216 |
| 45 | Drift Prairie and Missouri Coteau (ND) | 26625 | 7 | 310.5 |
| 46 | Drift Prairie and Missouri Coteau (ND) | 14238 | 8 | 270 |
| 47 | Red River Valley (ND) | 7821 | 6 | 45 |
| 48 | Missouri Coteau, James River Valley, and Prairie Coteau (SD) | 24587 | 9 | 315 |
| 49 | South and Eastern South Dakota | 15830 | 11 | 171 |
| Total | 1168624 | 8787.5 |
aFewer transects than indicated were surveyed in some years.
Anderson and Henny (1972) briefly described major waterfowl habitats in the surveyed area. Waterfowl counts within the various strata were initiated in years ranging from 1955 to 1965 (Table 2). We used data through 1981.
Table 2. Years in which waterfowl breeding-pair surveys and pond surveys were initiated, by stratum.
| Strata | Breeding Pairs | Ponds |
| 1-11 | 1957 | Not done |
| 12-20 | 1956 | Not done |
| 21-25 | 1955 | Not done |
| 26-40 | 1955 | 1955 |
| 41-42 | 1965 | 1965 |
| 43, 45-47 | 1958 | 1958a |
| 44, 48-49 | 1959 | 1959 |
aData missing in 1963, 1965, and 1966 for stratum 43.
Within each stratum, a systematic sample of transect lines was drawn. The starting line was selected randomly (Martin et al. 1979). Transects are 400-m (0.25-mile) wide and of variable length. Aerial counts of ducks and ponds are conducted each year along each transect, and a subsample of portions of transects is canvassed on the ground for ducks.
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