Other birds conspicuous in the potholes were Coot (Fulica americana), 
Horned grebe (Co us auritus), Pied billed grebe (Fog pas podiceps) 
American bittern (Botaurus lentigunosus), Virginia rail (Rallus ico 5, 
Sora rail (Porzana carolina), Black tern (Chlidonias niger), Long-billed 
marsh wren (Te odytes ustris), Short- ‘marsh wren (Cistothorus 
latensis), Redwinged blackbird (Agelaius phoeniceus). Muskrat 
tondstra zibethica) and Mink (Mustela vison) signs were also seen, Other 
species of considerable direct importance to waterfowl, although not occupying 
the potholes, were the skunk (Mephitis mephitis) and the crow (Corvus 
brachyrhynchos). 
Factors Affecting Vegetation Types 
There now arises the question: What causes the differentiation into 
vegetation types? The normal hydrarch succession as described by Weaver and 
Clements (1938) has been affected by land use and other factors to the point 
where there is a great variability in the vegetation of water areas. The 
fundamental processes remain unchanged. Submerged species give way to floating 
plants and emergents in the shallower waters, and the emergents give way to the 
sedge-meadow species in the moist soil of the shorelines, 
In addition to the processes which build up the bottom, making conditions 
unsuitable for one group of plants and creating conditions favorable for the 
invasion of another group, the water levels in these areas are extremely 
unstable. This instability may be as important as the soil-building processes 
in determining the successional stage of any portion of a water area, One 
year this portion may be covered by 12 inches of water and be typical of the 
floating stage; another year it may be dry and more typical of the sedge~ 
meadow stage. 
A consideration of the factors which may control the species composition 
of the various successional stages is given below. 
Area -- The area of the pothole (Table 2) seems unimportant as there was 
extensive overlap between the maxima and minima of the four types. A possible 
exception is Type A3, which was not found in potholes less than 3.1 acres in 
area, However, this was only slightly above the maximm for Types A2 and Ah 
and below the maximum for Al. Moreover, Type A3 potholes of smaller size were 
known to occur outside the boundaries of the study area, 
Depth -- There was an overlap of water depths in potholes of the four 
types. There was at least one pothole of each type between 1.2 and 2.0 feet 
in depth as measured in late August. These two figures represent the greatest 
minimum and the lowest maximum recorded depth for these types. 
Rate of Water Loss -=- With the exception of types A3 and Al, there was 
a similar overlap in this factor. The maximum of the former was less than the 
minimum of the latter, However, the difference appears relatively slight. 
Soils and Chemical Tolerance == A detailed soil map of the region was not 
available but it must be assumed that the soils of the region were somewhat 
heterogeneous and the chemistry somewhat variable. It is unfortunate that 
there were not facilities available for making a study of water chemistry, 
However, this was apparently not the major factor controlling the distribution 
of those species of vegetation found on the study area since the different 
vegetation types were represented not only in closely adjacent potholes but 
in different parts of the same pothole. 
