200 
IOWA ACADEMY OP SCIENCE 
precipitation, the nine counties in the northwestern corner having a 
yearly average of 28.16 inches, 77 per cent of which occurs between 
x^pril and September. According to the climatological maps published 
in the Atlas of Iowa, the region studied lies in a belt having a mean an- 
nual precipitation of 25-30 inches. Similarly there is a south to north 
decrease in temperature, the three northern tiers of counties having a 
mean annual temperature of 44 to 45 degrees. The physiographic and 
climatic conditions in the state are summarized in an excellent way in 
the Atlas of loAva referred to above. 
HABITATS. 
Owing to the relief there is more diversity in the biotic environments 
of the region investigated than is usual in the prairie-plains region. The 
ridges and knobs, varying in height, are sparated by small areas of flat 
or gently rolling prairie, and everywhere are lakes, ponds 'and sloughs 
of various sizes. The immediate area studied was on the water-shed be- 
tween the Missouri and Mississippi river systems, the lakes examined 
(lying near the Clay-Palo Alto county line) being the source of streams 
tributary to the different systems. Most of these lakes are drained by 
the Little Sioux river, which flows approximately through the center of 
Clay county, emptying into the Missouri, but a few are drained by tribu- 
taries of the Des Moines, which flows through Palo Alto county and is a 
tributary of the Mississippi. 
The habitats at the present time may be classifled as follows : 
UPLAND. 
Upland Prairie. Uncultivated areas, covered by the original vegeta- 
tion of grasses and herbs, are still to be found on some of the ridges. 
These areas are, however, becoming fewer in number yearly, as more 
land is placed under cultivation. (Figs. 1 and 2.) 
Grain Fields. The greater part of the higher land has, within the 
past thirty years, been placed under cultivation, and this has been mostly 
at the expense of the upland prairie areas. (Fig. 3.) 
Groves. In many places groves of soft maple, cottomvoOd, willow, and 
l)ox-elder liave been planted on the uplands. These are so open, however, 
as to have no appreciable effect on the terrestrial vertebrate fauna, with 
the exception of the l)irds, the local distribution of which they are pro- 
foundly modifying. (Fig. 4.) 
LOWLAND. 
Loioland Prairie {Meadows). The low, generally poorly drained, 
areas have in many instances been reserved for hay-land or pasture. In 
