CANADA 

Fig. 1. Distribution of stands of seeded nesting cover sampled in 
Minnesota, Montana, North Dakota, and South Dakota, 
age, vegetation removal practices, or fire after the nurse 
crop was sown and harvested, This generally implies no 
treatment after the first year of growth. The principal 
species sown included alfalfa, yellow and white sweet 
clover, and intermediate and tall wheatgrass. Occa- 
sionally, a stand’s mixture would also include a small 
amount of western wheatgrass, slender wheatgrass, crested 
wheatgrass, green needlegrass, or switchgrass. 
An inventory of land and water on National Wildlife 
Refuges and Waterfowl Production Areas in the glaciated 
prairie pothole region was made in 1976 and updated in 
1978 and 1979 (K. F. Higgins and D. A. Davenport, 12 
July 1979, unpublished data). A base of 65,205 ha on 
2,352 management units with a recent tillage history, po- 
tential sites for SNC establishment, was identified in this 
inventory. In 1976, about 14% or 9,072 ha met selection 
criterion | for SNC and essentially all had been sown since 
1968. 
During winter 1976-77, refuge and wetland district 
managers were asked to help identify stands that met 
selection criteria 1 and 2. A total of 327 stands appeared to 
fit the criteria for selection. Unfortunately, only 83 of 
these stands met both criteria when visited during the 1977 
field season. This initial discrepancy in field selection was 
primarily the result of two factors: (1) an emergency man- 
date to release units of public-owned grasslands for live- 
stock forage and hay to ameliorate the effects of extreme 
drought and low herbage production in this region during 
1976 and (2) a high transfer rate in refuge personnel. 
After the 1977 field season, another search of the up- 
dated files plus the annual increment of newly established 
stands increased stand samples to 138 in 1978 and 144 in 
1979. Some stands were not sampled each year because the 
3 
vegetation had been subjected to damage by intensive 
hailstorms or by tillage operations. 
Transect Location 
The prevailing wind direction in this region during fall 
and winter is from the northwest. Aerial viewing of sev- 
eral stands revealed a greater penetration of snowdrifts 
into the cover along the north and west edges. Therefore, 
vegetative transects were not located parallel to the north 
or west field edges. Transects did not conform to a specific 
direction or length because of the high degree of irregu- 
larity in stand size, perimeter, and shape, but were aligned 
with some obvious nearby physical features within or 
adjacent to each stand. These physical features were 
selected from either aerial photographs or surveyors maps, 
or by cruising the periphery of a stand. They were always 
selected before measurement of vegetation within a stand. 
The transect, the physical features, the spacing interval 
between measurement points, and the direction of meas- 
urements were all identified on field maps to assure a simi- 
lar degree of repeatability during later visits. 
The length of transects ranged from 150 to 375 m and 
averaged about 200 m. The length varied in relation to 
stand size and spacing between stations of measurement. 
Stations of measurement for residual cover samples were 
equidistantly spaced 6 steps apart in stands of less than 
4 ha and 10 steps apart in larger stands. Measurements of 
live vegetation were taken at even numbered stations for 
residual cover measurements. 
Vegetation Data Collection 
Five types of vegetative data were recorded annually 
along a linear transect in each stand, two types of residual 
cover measurements during early spring and three types of 
foliage records during summer. An effort was made to 
measure the same plots in each transect for both residual 
and live vegetation during all years. 
Between 15 March and 15 May, 100 visual obstruction 
measurements (Robel et al. 1970), 4 at each of 25 stations, 
and 25 height measurements (Jagtenberg 1970), 1 at each 
of 25 stations, were made per transect in the residual plant 
cover. In a few stands, measurements were taken at less 
than 25 stations due to unforeseen circumstances. Visual 
obstruction measurements were read on a 1.5-m by 5-cm- 
square pole from a distance of 4 m and a sighting height of 
1 m. The pole was painted white with decimeter and half- 
decimeter graduations and numerals painted red (Fig. 2), 
a slight modification of the pole description given by 
Robel et al. (1970). A visual obstruction value was read at 
a point on the pole where the residual vegetation began to 
hide the pole and no other part of the pole could be seen 
below this point. Measurements were rounded to the 
nearest half-decimeter. Height measurements were made 
by sliding a slotted 30-cm-diameter by 3-mm-thick plastic 

