504 
are as destitute of permanent mammalian life as though they were 
perpetual swamps. 
The land is exceedingly fertile, and every square rod that can not 
be kept under constant cultivation is a chronic annoyance to its 
owner. The fields are large—except in the vicinity of towns— 
running from 40 to 160 acres, or even more. Cultivation is thorough, 
and but few waste places along fences, ditches, etc., are permitted. 
There are but few hedges, orchards and groves are small and un- 
common, and but little land is left in permanent pasturage. Nar- 
row strips, barely two feet wide, along the wire fences, and belts 
a dozen feet in width each side of the roads—which are regularly 
laid out a mile apart—with limited spaces around the dwellings, 
are about all the land not turned up by the plough three years out 
of four. 
Apparently nothing but a veritable desert could be more un- 
favorable for mammalian life than these large well-tilled fields. 
They contain, however, considerable numbers of mammals at all 
times, and, really, an abundance of them at certain seasons. A 
common permanent resident of such fields—always present unless 
driven out by standing water—is the white-footed prairie-mouse, 
Peromyscus maniculatus bairdi. An illustration, based on repeated 
experiments, may throw some light on the abundance of this species. 
In large corn fields of 80 to 160 acres, when the corn was about one 
foot in height and was being repeatedly harrowed and kept almost 
absolutely free from weeds, I repeatedly set traps near the center of 
the field, at every tenth hill along the rows, with no regard to any 
indication of the presence of mice. The average result from one 
night’s setting was a white-footed mouse in about one trap in ten. 
Very rarely a specimen of the short-tailed shrew (blarina brevi- 
cauda) was taken. If these traps were set near the edge of the field, 
the proportion of traps containing animals was increased; and if 
near an old hedge, waste land, or roadside, specimens of the 
prairie-vole (Microtus austerus) might be taken, and the average of 
successful traps would rise to one in five for a single night. The 
same average would hold for traps set at the same distance apart in 
stubble or corn fields from which the crop had been cut and removed. 
My averages of successful traps set in the same way across a corn 
field, where the corn had been husked without cutting, was also 
about one in five. 
