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Waterfowl Production on the Woodworth Station
in South-central North Dakota, 1965-1981

Study Area

Each spring, millions of ducks migrate northward from wintering areas to nest in and near wetlands of the prairies, parklands, and woodlands of the north-central United States and south-central Canada. The reproductive success or failure of these duck populations is largely determined during spring and summer. An understanding of factors that affect the success or failure of nests is essential to duck management.

The Woodworth Field Station (WFS) of Northern Prairie Wildlife Research Center (NPWRC) was initially purchased as a Waterfowl Production Area with duck stamp dollars. Station field investigations began in April 1963 and included a historical land ownership survey, mapping of the vegetation, cultural features, land use, and wetlands, and a survey of wildlife (Bayha 1963,1964). Results of the 1963 and 1964 investigations are unpublished but are on file at NPWRC in Jamestown. The study area was expanded in 1964 to include all WFS lands subject to later purchase by the U.S. Fish and Wildlife Service (FWS); consequently, for 1963, only historical or land-use data are included in this report.

From 1964 through 1968, land-use treatments on the study area were maintained similar to those of prior years when the land was in private ownership. Since 1969, the station has been used for studying the response of wildlife to applied treatments of grazing, burning, idling, and annual cropping.

Even though our research did not address the effects of hunter harvest on local duck populations, we were aware of many changes in hunting styles and equipment through the years. For example, since 1964 hunters have had easier and greater access to fields and wetlands because of increased technology and off-road, primarily four-wheel drive, vehicles. Many hunters also used campers or established semipermanent housing on or near hunting areas, thus, increasing a persistent, and often intensive, hunting pressure on specific wetlands and public areas.

Long-term ecological studies of waterfowl production in the glaciated prairie pothole region of north central North America (Kiel et al. 1972; Smith 1971; Stoudt 1971, 1982; Leitch and Kaminski 1985; M. C. Hammond, unpublished data) have been relatively few in comparison to hundreds of short-term (<10 years) studies. With the exception of our study and the early waterfowl studies of M. C. Hammond, all other long-term waterfowl studies were conducted in Canada, mostly in the Aspen Parklands (Bird 1961) of the Prairie Provinces. Trauger and Stoudt (1978), Bellrose (1979), and Hammond and Johnson(1984) completed more recent reviews and analyses of some of these earlier long-term studies and associated data sets. The studies at the WFS were designed to address wildlife responses to land management changes (Miller 1971) and to evaluate their relevance to past and future management of these and other lands dedicated to wildlife production.

Scientific and common names of plants were taken from Stevens (1963); birds-Appendix B-and mammals-Appendix C-from Banks et al. (1987); reptiles and amphibians-Appendix D-from Collins et al. (1982); and fish-also Appendix D-from Robins et al. (1980).

Study Area

The Woodworth Study Area (WSA) is located in northwestern Stutsman County about 5 km east of Woodworth, North Dakota, and about 56 km northwest of Jamestown, North Dakota (Fig. 1). Altitude above sea level ranges from 561 m on the east to 594 m on the west and north. The study area is a large block of continuous habitat and is nearly 4 km². It contains about 1,231 ha (3,040 acres), of which 1,073 ha (2,650 acres) are federally owned (Fig. 2). A summation of the physical characteristics of the WSA appears in Table 1.

The WSA is on the Missouri Coteau (Winters1963), a biogeographic region extending from east central South Dakota through North Dakota into southwestern Saskatchewan, a distance of about 1,287 km. The Coteau is an area of morainic hills averaging 48 km wide. In North Dakota, the Coteau covers 25,584 km² and the northeast-facing escarpment rises 91-152 m above the adjacent Drift Plain. Unlike the slightly rolling, intensively farmed land to the east, the Coteau has irregular terrain with an interspersion of wetlands, native prairie pastures, hayfields, and a variety of grain crops. This large contiguous Coteau is of major importance to North American waterfowl (Stewart and Kantrud 1973).

The Coteau consists primarily of dead-ice moraine left from extensive glacial stagnation that followed advances of late Wisconsin glaciers. Most of the glacial drift on the Coteau has been aged at 9,000-13,000 years (Tuthill et al. 1964; Clayton 1966; McAndrews et al. 1967).

The WSA has two major glacial landforms (Winters 1963): hummocky stagnation moraine and outwash (Fig. 3). The hummocky stagnation moraine is rugged with an average altitude more than 564 m above sea level, consisting mainly of knobs and kettles. Dominant material is till. Linear patterns associated with end moraines are not apparent. Local relief sometimes exceeds 30 m/km² of land. Stagnation outwashes are extensive areas underlain by glaciofluvial material deposited in association with stagnating or dead ice. As a result of stagnation, the glacier disintegrated in place, causing the rugged glacial topography of the area, and the closely spaced hills and depressions. Many of the depressions contain wetlands of various sizes, shapes, and depths, often called potholes. Superimposed and collapsed outwash is included in this unit. This landform contains an ice-restricted gravel train discussed by Winters (1963).

The greatest number of potholes on the area occurs in the hummocky stagnation moraine and may exceed 40 basins per square kilometer of land. The stagnation outwash landscape has fewer pothole basins, but some of them are quite permanent because aquifers contained in the gravel train provide a high water table, seepage, and springs.

Parent materials of the soils of the area were deposited by glacial ice and are classified as glacial till. Glacial till is a random mixture of sand, silt, clay, pebbles, and stones with no sorting of the various-sized particles. The clay-sized fraction is dominantly montmorillonite (Omodt et al. 1968; Fig. 4)

The major soil association of the area is Buse-Barnes (Omodt et al. 1968; Patterson et al. 1968). This association occurs on hilly to rolling and undulating topography with pothole depressions common between hills, knobs, and ridges. This association has no major stream drainage. Surface runoff flows into many pothole depressions that are usually inundated for several weeks or longer in spring and summer.

Svea, Renshaw, Fordville, Sioux, Parnell, Colvin, and Tetonka soils also occur in this association. Svea soils occur on the concave side slopes and foot slopes of the knolls and hills. Renshaw, Fordville, and Sioux soils occur on small areas of outwash. Renshaw soils are moderately deep and Sioux soils are shallow over a gravel substratum. Parnell, Colvin, and Tetonka are the main soils found in wetland basins on the area.

Some predictive equations of soil moisture seem more related to wetland performance than 12-month precipitation amounts (Boyd 1981). Following William and Robertson (1965), conserved soil moisture was estimated in early May each year from the equation:

M = 0.36A + [0.37B - 0.2 (0.36A)]
+ 0.13C + {(0.30D - 0.2[0.36A
+ (0.37B - 0.2(0.36A)) + 0.13C]},


A = total precipitation during fall of the summer fallow period (August, September, and October in year t-2),
B = total precipitation during the first winter of the summer fallow period (November, t-2, to April, t-1),
C = total precipitation during the summer of the summer fallow period (May to October. t-1).
D = total precipitation during the second winter (November, t-1, to April, t).

The continental climate of the WSA is characteristic of much of the northern Great Plains, having a low precipitation-high evaporation ratio and cold winters-warm summers. The average number of clear days between sunrise and sunset is 112 per year. Average depth of frost penetration is 1.5 m and the extreme is 2 m (Bavendick 1952). Average relative humidity is 68%. Several studies have shown that for the past few hundred years, the northern grasslands have occupied their present areas with rather arid weather conditions (Will 1946; Dix 1964; McAndrews et al. 1967; Shay 1967; Wells 1970).

Precipitation records for the study area were taken in the town of Woodworth before 1966 and on the WSA since 1966 (Appendix A). During the study, total annual precipitation varied from a low of 23 cm in 1967 to a high of 58 cm in 1965. Mean annual precipitation for the years 1964-81 was 41 cm and the long-term (>50 years) mean annual for the vicinity was 44 cm (Bavendick 1952; Jensen 1972; Table 2). Precipitation is least and nearly always in the form of snow during winter. The first substantial rains of spring usually occur in early April, but sometimes in late March. Precipitation is greatest during summer, usually peaking in June.

Precipitation amounts decrease rapidly throughout the fall, and the first significant snowfall usually occurs in late November. Average mean annual snowfall is 86 cm for the study area. Mean date of first 2.5 cm or more of snow depth is 5 December and the mean date of last 2.5 cm of snow cover in spring is 25 March.

Mean annual temperature for the vicinity is 4°C (Bavendick 1952; Jensen 1972). January is the coldest month and July is the warmest (Table 2). The extreme high temperature for the vicinity during the study was 48°C and the extreme low -58°C. Mean length of freeze-free days is 120 and usually occurs between 20 May and 15 September.

Local topography of the area affects temperature in two ways. First, the WSA, on the eastern edge of the Missouri Coteau, is higher than surrounding physiographic regions. Temperatures on the WSA are usually from 1 to 3°C colder for this reason. Second, colder air accumulates in pothole depressions, often causing temperatures there to be several degrees colder than nearby uplands.

The prevailing wind flow is from the northwest with an average daily speed of 16 km/h. Winds are usually sustained strong breezes rather than occasional gales. Wind speeds are usually highest during the afternoon and lowest at night. At wetland sites, winds of 40-48 km/h often last for 6 h and have been known to last for as long as 15 h. Winds of more than 48 km/h have been observed to last longer than 6 h (Eisenlohr et al. 1972). Wind is an important factor affecting evapotranspiration rates on wetlands as well as on uplands.

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