. Control of field rodents in California. Rodents; Mammals. 28 California Agricultural Extension Circular 138 with earth. When a gopher is trapped out of a tunnel system another animal may later move in and occupy that system. Moles or mice occasionally use gopher burrows. Pocket gophers are active throughout the year (even in moun- tain areas, where they work beneath the snow and put the surplus earth in tunnels in the snow), and fresh workings may be found in any month. Surface activity is less on dry areas during the hot summer months; at this season new mounds may be entirely lacking on un
. Control of field rodents in California. Rodents; Mammals. 28 California Agricultural Extension Circular 138 with earth. When a gopher is trapped out of a tunnel system another animal may later move in and occupy that system. Moles or mice occasionally use gopher burrows. Pocket gophers are active throughout the year (even in moun- tain areas, where they work beneath the snow and put the surplus earth in tunnels in the snow), and fresh workings may be found in any month. Surface activity is less on dry areas during the hot summer months; at this season new mounds may be entirely lacking on unirrigated lands of the interior valleys. The animals are also less active during and just after a heavy rain. JW&UL^JUrn. **W. Fig. 11.—Method used by the pocket gopher in pushing earth out of the main tunnel through a lateral tunnel and onto the surface of the ground. The mouth of the lateral re- mains open while excavation is in progress; successive loads of earth are pushed in different directions from the mouth of the tunnel. Compare with figure 17. Breeding. On pasture lands and on uncultivated and unirrigated areas there is evidently a limited breeding season some time after the beginning of the rains, when green forage becomes available in quantity. On such areas there is probably a single annual brood. But in irrigated regions, especially in alfalfa fields where green forage is always available, breeding occurs throughout the year. In such places a female may bear more than one litter per season and up to 3 litters per year (Dixon, 1929; Miller, 1946). At altitudes of 5,000 feet and higher, breeding evidently occurs in June and July. Investigations at Davis indicate that the average litter is between 5 and 6, but may vary from 1 to 13. About one third of adult females were found preg- nant in April, none in September. The percentage of pregnancies increased with the size and age of the females (Miller, 1946). The young remain in the nest for several weeks after bi
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