
APPENDIX~--METHODS 
Census 
Much of the information gathered from the study area is related to size 
and condition of the waterfowl population. Since the value of the informa- 
tion depends largely on the accuracy of census, the methods used are described 
in detail. 
In the spring, before the broods had hatched, census of the adult birds 
was a fairly simple matter and involved merely walking around the margins of 
potholes, or once or twice through large overgrown areas to flush the birds. 
Since the study area is rectangular, rather than a linear transect, the 
major problem was to avoid duplicate counts of birds. By observing where a 
bird alighted after it was flushed from a pothole, the counter could eliminate 
it from counts made at the place where it settled. The problem was somewhat 
simplified by leaving potholes with large numbers of birds until late in the 
day. Whenever possible, birds on bare shores, where they could easily be 
seen, were not flushed. By using these methods, duplicate counts were kept 
to a minimum. Because of daily movements of birds across the boundaries of 
the study area, it was not intended that each bird be recorded as a resident. 
However, it is assumed that an index to the population density of each species 
was obtained. 
Birds were recorded as "pairs,” “lone drakes,” "lone hens," and "gathered 
birds” (presumably not breeding). For purposes of determining the breeding 
population in terms of breeding units or pairs, each pair, lone drake, and 
lone hen was assumed to represent a nesting pair. Undoubtedly some pairs were 
missed through not counting some of the grouped drakes, but it was impossible 
to determine which drakes had merely left their hens temporarily and which 
were through breeding for the season. The error was Kept to a minimum by 
estimating the spring breeding population for each species separately. The 
breeding population of all species is the sum of the peak number of breeding 
units of each species regardless of the time each peak occurs. A chance for 
error in this method of calculation lies in the possibility of pairs moving 
onto the area after the peak date. These late arrivals could not be added to 
earlier totals for the species. However, it is believed that very few birds 
arrived after the peak date. Another possibility for error is that some 
pairs might have broken up before the peak date, the drake to join other 
drakes and the hen invisible on the nest. Again, it is believed that little 
of this occurred before the species was present in peak numbers. The effects 
of these factors are evaluated in the section "Nesting Population." 
With the advent of the brood season, the difficulties of census increased. 
The habits of the brood hens and the young of the puddle ducks created a new 
problem, since many tried to hide rather than to flush into the open. A few 
attempted to escape overland. 
Most brood-census work was carried out as shown in figure 2 (A). A 
two-man crew started on one side of a pothole and zigzagged around opposite 
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