MOUSE PLAGUES, THEIR CONTROL AND PREVENTION. 309 

 PREVENTION OF PLAGUES. 



The prevention of plagues is comparatively easy. Their gradual 

 development affords opportunities to suppress them, even after the 

 damage has become quite extensive. The destruction of the mice 

 whenever they become at all numerous not only prevents considerable 

 damage, but is the best safeguard against serious outbreaks. Sys- 

 tematic poisoning must be relied upon to repress them when they are 

 obviously on the increase, but there are many inexpensive methods for 

 preventing this increase. The destruction of rank grasses and weeds 

 along fences and ditches, and particularly the pasturing off of the last 

 growth of alfalfa in fall, thus exposing the mice to the attack of 

 predaceous enemies, are important. Winter burning the dry vegeta- 

 tion on wild hay lands, on strips bordering fields, and on swampy or 

 otherwise w^aste areas in and about cultivated fields will aid mate- 

 rially in controlling them. The survivors may invade cultivated 

 fields, but there they can be more readily poisoned. Flooding the 

 fields in cold winter weather, when the mice quickly perish from 

 exposure, is an effective method in irrigated lands. Plows turn out 

 the burrows and nests of practically all the mice present and render 

 them easy victims for dogs, which when trained to kill mice can not 

 be too highly recommended as effective and inexpensive aids in con- 

 trolling the pests. 



Among the agencies w^hich check the increase of field mice none are 

 more important than their predaceous enemies. These mice, the 

 favorite food of many birds and mammals, active night and day, sum- 

 mer and winter, are preyed upon more than any other mammal. That 

 hawks, owls, gulls, crows, ravens, and herons among birds and 

 skunks, weasels, foxes, and badgers among mammals are persistent 

 enemies of field mice and other rodent pests has been often pointed 

 out. The protection and encouragement of these valuable allies of 

 the farmer can not be too strongly advocated. (PI. XXIV, fig. 2.) 



CONCLUSION. 



Mouse plagues are usually preceded for a season or more by notice- 

 able damage to crops, and success in checking them depends upon 

 prompt recognition of the early stages of outbreaks. When mice 

 first attract attention by increased nun^ibers and by damage here and 

 there, it is high time to destroy them. 



The work carried on by the Biological Survey in Nevada, especially 

 in Carson Valley, demonstrated that plagues can be controlled. The 

 systematic poisoning of 10,000 acres in Humboldt Valley during the 

 fall months, at a cost of about $4,000, would have prevented the 

 larger part of the damage, and it is safe to say would have saved 

 at least $175,000 worth of alfalfa. 



