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the observer and watch his movements, This was easily done by shooting at 
them with a .22 caliber rifle which kept most of them at such a distance that 
they could not watch proceedings. Nesting crows in some cases had to be 
destroyed, as they could not be driven from the vicinity and it was felt that 
hunting duck nests in their presence would lead to predation. Later it was 
found that if all the young of a crow nest were destroyed, the parents left the 
area, This was much more efficient, as it took considerable time to shoot the 
adults with a rifle. Eight crow nests were destroyed while 7 adults and 18 
young were shot from June 12 to June 26, Although few crows were killed by the 
use of the rifle, its great "scaring" range and easier portability made it 
superior to a shotgun. 
Locating Marked Broods == As soon as the clutches of marked eggs had 
hatched, searches were started for the broods. At first this was done 
intensively, and thorough searches were made of all potholes to which the 
broods might have gone after leaving their nests. This method produced no 
results and was abandoned in favor of making as extensive a coverage as 
possible of the entire area, 
Searches were conducted in three ways. The usual method consisted of 
traversing the margins of potholes on foot, moving slowly but creating 
considerable disturbance in an effort to drive broods into the open, Slow 
movement was necessary since birds which were approached too fast appeared 
to take cover and hide rather than flush into the open. This depended to 
some extent on the weather and the time of day. In the early morning or in 
the evening the birds were easier to flush than in the middle of the day. 
Still days were better than windy days, and most of the birds refused to flush 
if the wind was over 15 miles an hour. Some broods, particularly mallard and 
pintail, tended to circle the pothole ahead of the observer and often could 
be seen along the opposite shore sneaking through the marginal vegetation. 
For 9 days, at the time when most of the broods were hatching, Eugene F. 
Bossemmaier from the Delta Station furnished valuable assistance. Two men 
were not only able to cover a pothole twice as fast as a single man, but also 
could do it much more thoroughly. If they worked down opposite margins and 
met at the far side, any broods moving ahead of one man were blocked by the 
other and could be seen and sometimes captured, This was particularly 
successful when the drive was planned so that the two men met on a relatively 
straight shoreline where cover was not too dense. 
A second method consisted of a walking tour of the area to be searched, 
either in the early morning or in late evening. If the approach to a pothole 
was rapid and concealed the broods were often surprised on the open water and 
could be examined before they could reach cover. This was a rapid method and 
a large number of broods were seen in this way. But the coverage given to an 
individual pothole was not thorough since it was only on rare occasions that 
all broods were in the open at the same time, 
The most thorough but time-consuming coverage was obtained by: extended 
observation of a single water area during the early morning or in the evening. 
Little could be seen for the first 30 minutes, since the birds apparently 
became alarmed regardless of the concealment or silence of the approach, 
Ducks without young showed no sign of disturbance and would remain feeding or 
resting close to the observer both during and after the approach. Brood hens 
were apparently more wary and broods were rarely seen in the open for some 
time after the approach, After the observer had waited in a concealed position 
for 30 minutes to an hour, they began to emerge and in the course of the evening 
most of them could be seen. Apparently, even though the ducks could not see or 
hear the observer approaching, they became alerted, possibly by the calls of the 
other birds which the observer could not avoid disturbing and which required 
some time to become used to his presence. 
