Northern Prairie Wildlife Research Center
The driving concept behind the WSA was to have a sizable tract of land within the Missouri Coteau and close to the Northern Prairie Wildlife Research Center (now the Northern Prairie Science Center) in Jamestown, North Dakota (2). The Center itself was established in 1963 by the FWS to investigate migratory birds, with an emphasis on waterfowl, their life history, habitat needs, and potential for management. The Woodworth site was intended to provide a representative area for long-term research on habitat changes and responses by prairie waterfowl.
The study area is located in northwestern Stutsman County about 5 km east of the city of Woodworth. Elevation ranges from 561 to 594 MSL. Of the 1,231 ha, 1,073 are federally owned. The remainder consists of privately owned property whose owners allowed research to be conducted. Study area managers were Leo M. Kirsch (deceased) from 1964 to 1979, Kenneth F. Higgins during 1979-85, and J. Michael Callow from 1985 to 1989. Since 1989, the area has been managed from the Jamestown Center. The FWS is established on site and, in conjunction with the NPSC, coordinates management of the area to facilitate research.
The study area itself includes two major landforms: hummocky stagnation moraine and stagnation outwash moraine (3). Hummocky stagnation moraine is rugged with an average elevation of more than 564 m MSL, and consists mainly of knobs and kettles. The dominant material is glacial till. Stagnation outwash moraines are extensive areas underlain by glaciofluvial material deposited in association with stagnating dead ice.
Parent materials of the soils were deposited by glacial ice. They are considered glacial till, a mixture of sand, silt, clay, pebbles, and stones, without sorting by size. The major soil association is Buse-Barnes (4, 5). Svea, Renshaw, Fordville, Sioux, Parnell, Colvin, and Tetonka soils also occur, the latter three mainly in wetland basins.
Mean temperature for the area is 4 C, with January being the coldest month and July the warmest. The frost-free period averages 120 days, roughly between 20 May and 15 September. Prevailing winds are from the northwest, with an average speed of 16 km/h. Winds are typically strongest during the afternoon and calmest at night.
Since acquisition, most of the study area, especially native prairie, was managed primarily by prescribed burning, grazing, and leaving idle. Areas that had been cultivated were planted, either to native grasses or to a mixture of tame grasses and legumes that were recommended for waterfowl nesting habitat. Reseeded areas were managed by fire, scarification, and to a limited extent, fertilization. Little management of wetlands has taken place, although in recent years several wetlands that had been drained have been restored by the FWS.
Upland vegetation was monitored with a series of transects, and first flowering dates were recorded for many species (9). Each transect consisted of a number of Daubenmire quadrats. Twelve transects were established on the area in 1966, but two were discontinued after four years. During the first few years, only the end points of the transects were permanently marked, and individual quadrats were located by equidistant pacing. In 1973, all quadrats were marked. Each transect included 7-14 square quadrats, each 1.5 m on a side. Woodworth Field Station staff and volunteers surveyed the transects once each year during 1966-89, in summer or later. They recorded the plant species composition in each quadrat according to Daubenmire coverage classes. In addition, environmental variates were recorded for each quadrat, including soil type, moisture regime (upland, lowland, wet meadow, or wetland), slope, and aspect. Kirsch and Kruse (10) reported preliminary results based on four of the transects. Johnson (11) analyzed data for 1966-82, focusing on 15 of the most common plant species, of the 228 identified.
Photo stations were placed in 33 areas that represented the three major cover types on the study area: native grassland, seeded native grassland, and seeded dense nesting cover. Photos were taken during 1970-89 once in mid April or May before new plant growth began to dominate residual vegetation and again in August after the growing season. The photos visually depicted changes in vegetation structure and composition resulting from land-use treatments such as grazing, burning, and other types of habitat manipulation.
Breeding waterfowl were censused annually during 1965-89. Numerous counts were made during the earlier years, but beginning in 1972, two were considered adequate. These were made between 10 April and 10 July each year, but counts taken near 1 May and near 1 June ultimately were used for population determination. Censuses were made while walking or driving around the periphery of wetland basins. Total number of duck pairs ranged from 236 to 692, and averaged 492 during 1965-89. Averages by species are presented in Table 2.
Nests of waterfowl were searched for and monitored in most years. Three or four searches were made each year, usually beginning the first week in May and concluding by mid July. A cable-chain device, towed between two jeeps, was developed at the Station (12) and used to find nests by flushing attending females. (The device has since become a standard technique for waterfowl nesting studies.) Information recorded at each nest included number of eggs, stage of incubation, and habitat features of the nest site and surrounding field. Nests were revisited periodically to monitor fates of the clutches. During 1966-81, 3,832 duck nests were found, ranging from 65 to 424 per year (Table 2).
Broods of waterfowl were also counted, although the secretiveness of ducklings resulted in very minimal estimates of the total number (Table 2). Two brood counts were made each year, one in early July and one in early August. Counts involved visiting each wetland on the study area, and wading through wetlands to flush the birds. Species, age class, and number of ducklings were recorded.
Terrestrial bird communities were censused annually during 1972-95. Censuses were conducted on as many as 10 plots, but six plots were surveyed in all years. Census plots ranged in size from 4.86 to 10.12 ha. Each was visited about eight times each year, and locations of birds were recorded on field maps. After all surveys were done, territories were plotted and the number of pairs of each species was estimated. Details of these censuses are reported separately (13).
In addition, surveys were made each year of dancing grounds of sharp-tailed grouse (Tympanuchus phasianellus). Incidental observations were made of other species as well. For migratory birds, dates of first sighting each spring were recorded.
Beyond the monitoring programs described, numerous scientists conducted shorter-term studies based at Woodworth. Those done by NPSC staff are listed in Appendix 1. Table 3 mentions those performed by visiting scientists.