170 NORTH AMERICAN FAUNA [No. 55 



harsh. Grayish brown above, lighter brown or buffy gray below, very similar 

 at all ages and seasons. 



Measurements. Adults: Total length, 167 mm; tail, 82; foot, 18; ear (dry), 

 12, from crown, 9. Weight of adult female, 23.5 g; length, 162 mm; tail, 75; 

 foot, 17. 



Distribution and habitat. House mice are more or less common in 

 towns, houses, and at ranches over most of the inhabited parts of 

 Oregon, and in the more fertile parts in the fields and meadows. 

 Some of the widely isolated ranches in the arid part of the State may 

 still have escaped the inroads of these pests, but eventually they 

 probably will be invaded. 



Introduced from Europe in the early days of the settlement of 

 North America, these mice have followed so closely the advance of 

 civilization that they now outnumber many of our native rodents 

 over much of the continent. 



General habits. House mice are largely dependent on the works 

 of man, occupying houses, barns, and outbuildings, feeding largely 

 on stores of grain and foods of any kind within their reach, hiding 

 in rooms, cellars, and boxes and making long journeys from place to 

 place in boxes of household goods or loads of supplies. Once estab- 

 lished they multiply rapidly, and with the protection afforded by 

 buildings, often become so numerous as to extend out into the fields 

 and meadows, under cover of grass and grain, until they overrun the 

 most fertile parts of the valley country. They burrow into banks, 

 under walls, rocks, or logs, and establish safe retreats of their own 

 and show more skill than most of our native mice in avoiding enemies. 

 While largely nocturnal, they are often out voluntarily searching for 

 food in daylight and seem to see equally well in light or dark. They 

 climb and dig and gnaw holes through boards and walls and are not 

 easily restrained from getting at supplies. 



Breeding habits. House mice breed more or less regularly at all 

 seasons of the year, if food is abundant and comfortable quarters 

 assured. Six to thirteen young are recorded for the litters, and the 

 period of gestation is given as 21 days. The 12 mammae in adult 

 females are arranged in 3 pairs of inguinal and 3 pairs of pectoral, 3 

 on each of 4 separate mammary glands. 



Food habits. These mice are more than usually omnivorous for 

 rodents, eating not only grains, seeds, nuts, and fruits, but all kinds 

 of meat, fat, butter, cheese, milk, cream, bread, cake, vegetables, and 

 any cooked or uncooked food they can get. They do not lay up stores 

 for winter and are active at all seasons. 



Economic status. These are among the most annoying and de- 

 structive of mouse-size rodents, because, concentrated about buildings, 

 granaries, stacks, and grainfields, they constantly devour and 

 destroy valuable property. In the fields and open country they are 

 to some extent controlled by such enemies as owls, hawks, shrikes, 

 weasels, skunks, foxes, cats, and other predatory animals, and to 

 some extent about buildings by house cats. Trapping, poisoning, 

 and other methods of destruction are often necessary. Directions for 

 the best methods of combating such pests are always available from 

 the United States Department of Agriculture or State agencies. 



