254 ECONOMIC MAMMALOGY 



beneath and into buildings by the free use of cement in foundations and 

 basement floors, tin and sheetiron about the edges of doors to prevent 

 gnawing, plugging all holes and openings except such necessary ones 

 as drain pipes, which may be protected by wire screens. 



Cooperative campaigns over large areas are often necessary, so that, 

 after reducing the rodents locally, others may not flow in from sur- 

 rounding breeding grounds. In such campaigns the United States, 

 with its trained workers, often cooperates with local authorities or or- 

 ganizations. 29 In one year the Biological Survey directed the use of 

 1610 tons of poisoned grain in the destruction of prairie-dogs and 

 ground squirrels on over 18,000,000 acres of farm and range lands, 

 with the cooperation of 132,000 farmers and stockmen. The saving 

 of crops and range grass thereby, based upon estimates by the farm- 

 ers and stockmen themselves, amounted to more than $11,000,000 for 

 the season. 30 Considerable of the expense of such campaigns is some- 

 times covered by the sale of pelts of the animals killed, 25,000 pelts 

 from the Imperial Valley campaign of 1919-1920 having brought 

 $3i,ooo. 31 Organized rabbit drives, found effective in the West, are 

 discussed on a subsequent page. 



Much of the damage by rodents may be prevented by constant watch- 

 fulness and the free and intelligent use of traps and poisons when- 

 ever necessary, and especially by prompt measures for the suppression 

 of the rodents when they begin to inordinately increase, before the 

 threatened uprising assumes plague proportions. The destruction of 

 1000 rodents in the incipient stages of an outbreak means the preven- 

 tion of the breeding of many thousands of others. 



Bounties have not proved very effective in the suppression of rodents. 

 At least as far back as 1749 bounties were paid on squirrels in Penn- 

 sylvania. 32 Bounties are discussed at some length in Chapter xxvu, 

 on Legislation Concerning Mammals. 



Though rodents sometimes destroy all the seeds of forest trees in 

 small isolated areas during seasons when seeds are scarce, and other- 

 wise damage forests to some extent, the seeds they bury or other- 

 wise store during seasons of plenty aid in natural reforestation after 



29 Bell, Cooperative campaigns for the control of ground squirrels, prairie-dogs 

 and jack rabbits, Yearbook U. S. Dept. Agric. for 1917, pp. 225-233. See also Kel- 

 logg, The ground squirrel control program, California Dept. Agric. Special Pub. No. 

 109, 1931. Alexander, "Control, not extermination," of Cynomys ludovicianus ari- 

 zonensis, Journ. Mammalgy, xm, 302, 1932. 



80 Bell, Death to rodents, Yearbook U. S. Dept. Agric. for 1920, p. 431. 



81 Dixon, Rodents in Imperial Valley, Journ. Mammalogy, in, 136-146, 1922. 

 32 Rhoads, Mammals of Pennsylvania, p. 55, 1903. 



