396 Biology in America 



network of runways of the prairie vole. Upon digging into 

 the burrows at the base of apple trees, I found many twigs, 

 4 to 6 inches long, that had been entirely stripped of bark 

 and left lying in little piles. I had no difficulty in finding 

 where the twigs had been severed from low-growing branches 

 and the tips of sprouts, and in distinguishing, by the smaller 

 tooth marks, the cutting done by mice from that done by 

 rabbits. Whether the twigs had been first stored and after- 

 wards fed upon in cold weather, I was unable to determine, 

 for I found none with bark remaining upon them. Probably 

 they were carried to the burrows merely for leisurely but 

 immediate consumption. 



"Contrary to the usual habits of voles in our Northern 

 States, this injury had been done during mild weather. Up 

 to December 18 the season had been very warm and open. No 

 snow lay on the ground for more than twenty-four hours. 

 Ordinary food, such as grass, seeds, and grain, was abun- 

 dant, so that the only explanation for the injury to trees 

 seems to be the vast numbers of voles present and their pref- 

 erence for a partial diet of bark. 



"Voles, however, were not the only animals abundant in 

 the orchard. Rabbits, both cottontails and jacks, were there 

 in great numbers, and already had begun to eat the bark on 

 the trunks of some of the trees and on the low limbs, and to 

 cut the tips of branches and sprouts within their reach. 

 Later, when cold weather set in and snow covered the ground, 

 they also seriously damaged the trees. ' ' 4 



"Experiments show that the average quantity of grain 

 consumed by a full-grown rat is fully 2 ounces daily. A 

 half -grown rat eats about as much as an adult. Fed on grain, 

 a rat eats 45 to 50 pounds a year, worth about 60 cents if 

 wheat, or $1.80 if oatmeal. Fed on beefsteaks worth 25 cents 

 a pound, or on young chicks or squabs with a much higher 

 prospective value, the cost of maintaining a rat is propor- 

 tionately increased. Granted that more than half the food 

 of our rats is waste, the average cost of keeping one rat is 

 still upward of 25 cents a year. 



" If an accurate census of the rats of the United States were 

 possible, a reasonably correct calculation of the minimum 

 cost of feeding them could be made from the above data. 

 If the number of rats supported by the people throughout 

 the United States were equal to the number of domestic ani- 

 mals on the farms horses, cattle, sheep, and hogs the mini- 

 mum cost of feeding them on grain would be upward of $100,- 

 000,000 a year. To some such enormous total every farmer, 



4 Lantz, "An Economic Study of Field Mice." Biol. Survey, Bull. 

 31, pj>. 25-9. 



