Table 12.--Percent of broods in each wetland type, by years, 1950-53 
[Based on 1,618 brood observations ] 

Percent of total . Percent of broods 
Wetland type pothole acreage 1950| 1951] 1952! 19531 Average 
Intermittent’ areas 0.0 
Temporary marshes 3 
Shallow marshes 2.0 
Deep marshes 32.6 
Open-water areas 70.6 65.1 
Total 100.0 100.0 100.0 
the use of the deep marshes and shallow marshes, and a decrease in use of open- 
water areas. This was probably due to the thinning of marsh vegetation by 
rising waters. Many of the areas heavily used in 1952 and 1953 were dry during 
most of the brood season in 1950, and shallow or dry in 1951. Furthermore, 
some of the large open-water areas previously much used were so bare and wind- 
swept in 1952 and 1953 as. to be less attractive to broods. 
Much of the use of the marsh areas occurred early in the season, with 
broods appearing more and more on open water as the season progressed and the 
smaller, less permanent areas developed dense vegetation and decreased in depths, 
becoming unattractive. This was particularly marked in 1951, when no broods 
were found on open-water until 1 month after the first brood was seen, and not 
until 26 broods had been counted on marsh areas. 
Species differed considerably in their preferences. Table 13 indicates 
that the diving ducks and the gadwall definitely favored open water areas. 
The other river ducks, particularly the mallard and the pintail, made much 
more use of the deep marshes. The ruddy duck was somewhat intermediate. 
Observations of brood behavior have indicated that the selection of 
brood-rearing habitat depends on the availability of a means of escape from 
predators. . This may be furnished by cover sufficient to conceal the brood but 
not so dense as to restrict the movements of the young. On the other hand, a 
-INeans of escape may be provided by open water of sufficient size and depth 
that broods can dive to escape their enemies. The first means of escape is 
furnished most often by deep marshes and the margins of some of the open-water 
areas, particularly those in which the vegetation is undisturbed. This is the 
type of habitat sought primarily by puddle-duck broods. The large open areas, 
deep enough to furnish escape by diving, are heavily used by diving-duck and 
gadwall broods, whether or not good escape cover is available. 
Some generalizations about habitat preferences of broods on the Waubay 
area may be made: 
1. No broods were found in less than 5 inches of water in any cover type. 
WL 
