144 
JOUKNAL OF MAMMALOGY 
question is irrigation and Bermuda grass. Under the original desert 
conditions food and ground suitable to burrow in were the chief factors 
that limited the distribution of the gopher. 
Bermuda grass was abundant along the Colorado River near the 
intake of the main Imperial canal in 1910. This grass was carried 
all over the irrigated land by seed which was carried down stream by 
the irrigation waters. The banks of irrigation ditches afford safe 
breeding dens and temporary refuge to gophers. The root-stalks of 
the Bermuda grass, which flourishes along the margins of the canals, 
furnish these animals a constant, abundant, and acceptable food supply. 
The removal by man of many of the natural enemies of the gopher 
greatly improved the living conditions of these rodents, so that a larger 
percentage of the young reached maturity, and bred, thus hastening 
the rapid increase. While man has caused the death of many gophers 
through drowning, when the fields are flooded during irrigation, a large 
breeding stock always remains along the canal banks which are never 
flooded. 
Gophers prefer to work in sandy soil. Hard or “tight’^ ground is 
avoided. This is well illustrated in districts seven and eight, both 
of which have a great deal of sandy ground and a corresponding abun- 
dance of gophers. 
In district seven, 100 gophers have been trapped along one mile of 
canal in several places. In district eight, which is across the valley 
from district seven, there is a record of 400 gophers having been trapped 
in a short time along two miles of badly infested canal. Gophers are 
now also abundant along the main canals in Lower California. At 
Eastside and Sharp's headings they were found in March, 1921, to be 
present, as determined by actual trapping by the writer, at the rate 
of 105 per mile. 
Gophers do not hesitate to invade fields adjoining the canals and 
here they destroy much alfalfa and other crops. If it were not for the 
fact that gophers are drowned out by flooding during irrigation they 
would soon become unendurable pests. There is no chance to starve 
out the gophers since they can always fall back on the Bermuda grass 
roots. The gophers often carry Bermuda grass root-stalks about in 
their cheek pouches and thus aid in the spread of this grass. About 
one-third of the gophers trapped by the writer at Eastside Heading in 
March, 1921, had Bermuda grass in their cheek pouches. All of the 
gophers thus caught were very fat, being fatter than the muskrats 
taken at the same time. 
