1967] Willey C5 f Willey — Populations of Grasshoppers 
49 
distinguish the two species in flight by shade differences, banding of 
the wing, and flight behavior. Here again, any individuals which 
could not be checked with certainty were not counted. All the 
observers were experienced enough to be accurate by the time they 
started work on these localities. Later in the season, several other 
bandwing species begin to appear, but they are all easily distinguished 
in flight from A. conspersa. 
The most productive time for counting the population was between 
10 AM and 4 PM on clear warm days. Since the peak for each 
population lasts only two weeks, and three or four observers take an 
average of 1% hours to count a sample of 200, time is an important 
factor. 
A second method was to collect about 50 specimens as nearly at 
random as possible. This usually took longer than merely counting 
200 in the field and required additional curatorial time. However, 
we did collect from large populations and in this way we could 
check on the frequency of various shades of presumed heterozygotes. 
Recently, laboratory breeding of individuals from selected localities 
has proved successful, and the genetic analysis when completed will 
be reported later. 
Results and Discussion. 
The accompanying maps and table (figs. 1 and 2, and plate 7) show 
the wing-color proportions of each sampled locality between Sapinero 
and Green Mountain Reservoir. The most striking difference be- 
tween the populations of the North and South Rims occurs within 
the National Monument itself. In more than three years of intensive 
sampling, populations of the monument’s North Rim have never been 
observed to produce a yellow-winged individual (11=1355), whereas 
the South Rim’s population varies in a dine from <65% yellow in 
the west to >90% yellow at the eastern boundary. 
First we shall consider the physical properties of the canyon rims. 
On both the South Rim and North Rim the grass habitat is quite 
discontinuous. Grassy openings in the chaparral are often separated 
by several hundred yards of dense brush. In this way, the rim 
populations are broken up into semi-isolated units which show sharp 
clinal variation which is less dependent on distance than on the 
density and impenetrable nature of the chaparral barrier. For ex- 
ample, the populations on the South Rim (fig. 1) along the relatively 
continuous grassy areas locality from Sunset View (#3) to Gunnison 
Point (#6), a surface distance of three miles, are stabilized at 33% 
to 36% orange. At the campground (#7) the proportions vary from 
