252 ECONOMIC MAMMALOGY 



eats about 30 grams, or a little over an ounce, of green food every day. That 

 runs up to 23 pounds in a year. A hundred mice will stow away over a ton 

 of green grass or clover in a twelvemonth. A hundred mice to an acre is 

 not an unusual number in meadows favorable to their habits, while in "mouse 

 years" the number has been estimated at thousands to the acre. 



Mouse plagues, disastrous as they are locally, are of minor importance in 

 comparison with the steady yearly drain on crops by the mice over the country 

 at large in normal years. Even as few as 10 meadow mice to the acre on 100 

 acres of meadow would take about n tons of grass or $ l / 2 tons of hay a year. 

 This number, on the 65,000,000 acres of hay raised in the 38 mouse- states 

 of the country, would cause a loss of over 3,000,000 tons of hay a year, or 

 a money loss of some $30,000,000 annually in hay alone. The number of young 

 in a litter ranges from two to nine, and one pair averages five to the litter. 

 At this rate of increase, allowing equal numbers of males and females, and 

 the young beginning to breed at 46 days old, the total increase from one pair, 

 if all lived and bred, would be over 1,000,000 individuals at the end of a year. 

 If all were confined to one acre of ground, this would mean over 20 mice to 

 every square foot. 



The annual damage by the introduced European rats and mice in 

 warehouses in the United States has been estimated at $200,000,000, 

 and the annual damage by native rodents to crops in the western 

 United States has been placed at $300,000,000. 21 In 1908 it was esti- 

 mated that the annual loss to agriculture and horticulture in the United 

 States, from the depredations of ground squirrels alone, was 

 $ 1 0,000,000. 22 The damage done to crops and range by native rodents, 

 chiefly prairie-dogs, ground squirrels, pocket gophers and jack rabbits, 

 in 8 states in 1917 was estimated as follows: Montana, $15,000,000 

 to $20,000,000; North Dakota, $6,000,000 to $9,000,000; Kansas, 

 $12,000,000; Colorado, $2,000,000; California, $20,000,000; Wyo- 

 ming, 15 per cent of all crops; Nevada, $1,000,000; New Mexico, 

 $3,600,000; Virginia, in 1915, in a single county, $200,000 damage 

 to orchard trees by pine mice alone. 23 In Colorado in 1918, 14,000,000 

 acres of land were said to have been infested with prairie-dogs and 

 1,000,000 acres with Wyoming ground squirrels, the annual damage 

 therefrom, at only 10 cents an acre, amounting to $1,500,000, which, 

 added to $500,000 damage from other rodents, would make $2,000,000 

 per anum, a conservative estimate. 24 To all estimates of damage must 



21 Vorhies and Taylor, Life history of the kangaroo rat, U. S. Dept. Agric. Bull. 

 No. 1091, p. 2, 1922. Taylor and Loftfield, Damage to range grasses by the Zuni 

 prairie-dog, U. S. Dept. Agric. Bull. No. 1227, 1924. Henshaw, Policemen of the 

 air, Nat. Geog. Mag., xix, 79, 1908. Bell, Cooperative campaigns for the control 

 of ground squirrels, prairie-dogs and jack rabbits, Yearbook U. S. Dept. Agric. for 

 1917, pp. 225-233. 



22 Bailey, Farmers' Bull., No. 335, p. 6, 1908. 



23 Bell, Death to rodents, Yearbook U. S. Dept. Agric. for 1920, pp. 422-423. 



24 Burnett, Rodents of Colorado in their economic relations, Office Colorado State 

 Entomologist Circular No. 25, p. 6, 1918. 



