The information in the present account was obtained by observing animals
in the field, and by examining trapped animals that were brought into
the laboratory. Five hundred individuals were caught in snap-traps, and
forty additional voles that were marked were captured a total of 157
times. More than 90 per cent of the specimens were trapped at Lawrence,
Douglas County, Kansas, but voles were examined also in Ellsworth,
Atchison, and Jefferson counties, Kansas, and in Douglas County,
Illinois. My data pertain to _Microtus ochrogaster_ in the above named
areas from October, 1945, until August, 1946. The findings may not be
typical of this species in other areas and in other years.
The museum special traps were used both with and without bait. The bait
consisted of a piece of walnut meat on the treadle. By placing the trap
crosswise in the runway, voles were captured whether or not the treadle
was baited. Immediately upon removal from the trap, each vole was placed
in a white flannel sack, one sack sufficing for several voles when
necessary. In this way the loss of ectoparasites was kept to a minimum.
The fleas were counted, and the numbers of lice and mites were
estimated; some specimens of ectoparasites were saved for
identification.
The voles taken in live traps were marked and released. The marking was
done by cutting off one or more toes in such a manner that the vole
could later be identified. From left to right, the toes were assigned
numbers from one to five on the left hind foot, and by tens from ten to
fifty on the right hind foot. Number 33, therefore, was assigned to the
one vole of which the middle toe of each hind foot had been cut off.
Each time an animal was captured alive, it was weighed, specimens of
fleas, lice and mites were preserved, and the external appearance of the
reproductive organs was noted. The extent of the molt line, if the vole
was molting, was recorded. Corresponding data were kept for each dead
vole caught in a snap trap.
Assistance is acknowledged from Professors E. Raymond Hall, A. Byron
Leonard, Worthie H. Horr, and Donald F. Hoffmeister; and I have had also
much helpful advice from Professors W. J. Hamilton, Jr., and P. C.
Stone.