Burrows of the Sacramento Valley pocket gopher in flood-irrigated alfalfa fields
AuthorMilton A. Miller
Author AffiliationsMilton A. Miller was Professor of Zoology and Zoologist in the Experiment Station, Davis.
Hilgardia 26(8):431-452. DOI:10.3733/hilg.v26n08p431. January 1957.
This paper discusses patterns and statistical characteristics of burrows dug by the Sacramento Valley pocket gopher (Thomomys bottae navus Merriam) in flood-irrigated alfalfa fields, and the relationship of burrowing activity to soil conditions and irrigation schedules. Suggestions for improvement of gopher control derived from this study are given.
Functionally, a gopher burrow comprises two unequal parts: (1) a loose network of main and lateral feeding tunnels which lie within one foot of the surface (mode at 6- to 8-inch depth) and comprise 80 per cent of total tunnel footage; and (2) a deeper tunnel system which centers at 20- to 22-inch depth and connects with nests and food caches. Typical burrows have several steep tunnels which end blindly at various depths down to nearly seven feet and probably serve for drainage. Burrows concentrate in or near field levees which are often extensively undermined.
Normally, only one gopher inhabits a system, but considerable turnover in occupancy of established burrows is indicated.
The average burrow includes 107 ± 21 feet of cylindrical tunnels, 2.6 ± 0.08 inches in diameter, giving a volume of 3.87 ± 0.69 cubic feet; 8.6 ± 2.8 feet of recently plugged tunnel; about two nest chambers and an occasional food cache.
Following flood-irrigation, fresh gopher mounds reappear on about the second day, reach peak production during the latter half of the first week, and then decline to a low level. Burrowing is correlated with soil moisture, the optimum ranging between 15 and 17 per cent with markedly less mounds produced under wetter or drier conditions.
Between irrigations, each gopher excavates a daily average of 5.13 ± 0.71 pounds of soil (dry weight), an annual turnover (at this rate) of about a ton.
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