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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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