The effectiveness of the "burrow-builder" is dependent 
upon the gophers finding the artificially-constructed runway and 
using it long enough to find the poisoned bait. In order to make 
this possible, the artificial burrows are constructed at a depth 
so as to intercept the greatest number of natural gopher tunnels 
(figure 4). This will vary with soil conditions and the species 
of gopher being controlled. The distance between artificial bur- 
rows across an area is determined by density of gophers and the 
species involved (figure 5). 
What Has Been Done 
The machine has been field-tested against the plains 
pocket gopher (Geomys bursarius) in alfalfa fields in Weld County, 
Colorado. All tests were conducted in the spring of 1959 when the 
sandy-loam soil was moist. Gopher populations were estimated to 
be 10 to 15 animals per acre. A good artificial burrow was con- 
structed at a depth of 9 inches, and the interval between these 
burrows across the field was 25 to 30 feet. Between 3 and 4 pounds 
of bait were used on each acre and the average treatment time was 
10 minutes. At this rate, one man could treat approximately 50 
acres per day at a cost of $1.50 per acre (80 cents for bait, 30 
cents for labor, and 40 cents for rental of tractor). Under these 
conditions 90 to 100 percent control was obtained. 
Baits used in these tests were formulations of Compound 
1080 and milo maize, and strychnine and milo maize with the addi- 
tion of a small quantity of Erigeron extract to increase acceptance. 
Recommended baits for use in the "burrow-builder" may be obtained 
by contacting district offices of the Branch of Predator and Rodent 
Control. 
Soil conditions in the mountains of Colorado during the 
summer of 1959 generally were too dry for efficient use of the 
"burrow-builder,"' so tests involving the mountain pocket gopher 
(Thomomys talpoides) were carried out in October in mixed alfalfa- 
grass hayfields in Larimer County. The soil, moistened by recent 
rains, was a sandy-clay-loam type with some rocks. Gopher popula- 
tions were estimated to be 10 to 15 per acre. A good artificial 
burrow was constructed at a depth of 6 inches, and the interval 
between these burrows across the field was 20 to 25 feet. About 
three pounds of bait were used on each acre. Under these conditions 
85 to 100 percent control was obtained. | 
Baits used in the tests on mountain gophers were formu- 
lations of Compound 1080 and whole oats. The whole oats were found 
to be more acceptable to these gophers in laboratory tests. 
