MOBILITY OF DUCKS IN THE BREEDING SEASON 
Breeding pairs 
One of the most important considerations in a study of the use of habitat 
is how readily, and for what distances, the ducks can move: how mst the habitat 
be distributed in order to meet the needs of the birds? Hochbaum (1944) has 
defined territory as an area defended against other males of the same species 
and where the pair spends most of its time: an area having water, a loafing 
spot, nearby nesting cover, and food. 
There is, in pothole country, a modification of this pattern as indicated 
by movement of birds from water area to water area. Repeated observations on 
a series of potholes in 1951 showed that pairs did not generally remain for any 
length of time on one pothole but moved from one to another. 
In 1950, a pair of cinnamon teal took up residence on the study area. 
Since this species is extremely rare in eastern South Dakota, it was assumed 
that there was only one pair in the locality. Figure 19 shows where one or 
both members of this pair were seen on occasions from June 20 to July 26. It 
is safe to assume that they also used other potholes, since several other visits 
to the entire area south of the road and the two potholes northeast of the inter- 
section failed to reveal the birds. 
In 1952 and 1953, observations were made on birds individually marked for 
recognition. Enough was learned from these birds to demonstrete clearly that 
the blue-winged teal has a definite home range which encompasses a variable 
amount of land and includes several potholes. Figure 20 shows the minimum home 
range of one of the better-known pairs. The pair together was seen on seven 
different potholes, and the drake alone was seen on six. Most of these local- 
ities were defended by the drake. This home range was also used by other pairs 
with overlapping home ranges. The only friction occurred when a second pair 
appeared at a pothole at the time this resident pair was using it. The maximum 
size of the average home range was not determined by this study, but it was 
possible, by plotting upon a map all the potholes used by a marked pair, to com- 
pute the mean radius? of the minimum home range. The home range could be no 
smaller, but it could be, and probably was, larger. It should be emphasized 
that a pothole, even if used many times by a pair, was used only once in com- 
puting the mean radius, since some potholes (trapping sites, for instance) were 
under observation more of the time than were others. 
Mean radii of the home ranges of 11 pairs, determined by this method, 
averaged 0.18 mile and varied from O (one bird observed several times was al- 
ways on the same pothole) to 0.44 mile. Several territorial sites within each 
of these home ranges were, in many cases, defended in the manner described by 
Hochbaum (1944) as territorial defense. One loafing log appeared to fit the 
familiar picture of a nesting territory, as a pair of teal was seen resting 
there for several days. However, when the trap was set up by this log, four 

The mean radius is determined by establishing the midpoint of a number of 
observations, measuring the distance from that midpoint to each observation, 
and calculating the mean or average distance. 
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