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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- sects^a	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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