202 
IOWA ACADEMY OP SCIENCE 
It has been shown elsewhere® that the prairie region cannot be merged 
Avith the forested region of the states east of Illinois, but that neither, on 
the other hand, can it be classed Avith the arid plains. The environic 
conditions differ from those of the eastern forest region in being more 
arid and principally characterized by grass associations, and from the 
arid plains in being less arid and supporting a greater tree growth. Fur- 
thermore and in harmony with these conditions, the terrestrial vertebrate 
fauna consists almost entirely of a mixture of eastern and western forms. 
In vieAV of these conditions the region must be considered as a transition 
area." 
This point aaqII not be discussed further, but it should be noted that 
the different elements in the fauna of nortliAA^estern loAA’a occupy, as a 
rule, different habitats — the prairie forms being Avestern, and the mar- 
ginal forest forms eastern types, AAdiile in general it is those associated 
AAutli aquatic conditions that occur in both regions. For instance, it is in 
the marginal forests along the shores of the streams and lakes (also noAV 
in the groves) that one finds the Blue Jay, Baltimore Oriole, Red-headed 
Avoodpecker and many other forms characteristic of the forest of east- 
ern North America ; it is on the prairie that one finds the prairie Hare, 
Thirteen-lined Spermophile, Franklin Spermophile, Western MeadoAV 
Lark, Grasshopper SparroAA% Prairie Chicken, BurroAAfing Owl, and many 
others, that are distinctly arid plains forms ; AAdiile it is in the aquatic hab- 
tats that one finds the generally AAudely distributed Avater birds and 
amphibious mammals. That the elements in the amphibian-reptile fauna 
shoAV the same distribution is, I believe, shoAvn by the folloAving table in 
Avliich an attempt has been made to summarize briefly the local and gen- 
eral distribution of the forms. 
®Ruthven, Alexander G., loc. cit. 
^Tn his former paper on the vertebrate fauna of the prairie region the writer did 
not attempt to discuss the literature, intending- the paper as a contribution of addi- 
tional data to the subject. To those not familiar with the literature it should be 
pointed out that Allen (Bull. American Museum of Nat. Hist., lAh p. 231, and The 
Auk, X, p. 129) has called attention to the fact that the eastern forest and plains 
faunae interg-rade in the prairie region, in the following words : “The transition 
between the Humid and Arid Provinces is nowhere abrupt; they gradually merge into 
each other everywhere along their line of junction, as the prairies of the Missis- 
sippi Valley gradually become more arid and take on the characteristic aspect of 
.the plains. There is thus here the usual ‘transition’ belt occurring between contiguous 
faunal areas.” More than this, he has also called attention to the fact that the eastern 
birds by clinging to the borders of the streams push beyond the eastern forest region 
into the prairie-plains region (The Auk, X., p. 132). 
