HOUSE MOUSE 103 



young, not fully grown, were captured about the barns in Yosemite Valley 

 at the end of December. The broods elsewhere are known to average 

 between 5 and 6. 



Alexandrine Rat, Rattus rattus alexandrinus ( Geoff roy) 



Field characters. — The typical 'rat' of household notoriety; tail longer than head 

 and body; tail scaly, with but few short hairs (fig. 12a) ; pelage coarse, with many long 

 overhairs. Head and body 7^ to 8 inches (182-205 mm.), tail 8% to 10 inches 

 (213-250 mm.), hind foot about 1% inches (36-39 mm.), ear from crown about 1 inch 

 (23-26 mm.) ; weight under i^ pound. Upper surface of body plain grayish brown or 

 yellowish brown; under surface uniform dull yellowish; feet dusky, not white. 



Occurrence. — Not native; now well established, both about settlements and on wild 

 land nearby, at various localities on west side of Sierra Nevada. Eecorded at Snelling, 

 Lagrange, and El Portal. Lives in houses and in thickets and drift debris along banks 

 of rivers. 



The Alexandrine or 'Roof Rat is one of the few alien species which has 

 become well established in the Yosemite region. Its introduction was wholly 

 unintentional on the part of man, an unwelcome incident in his occupation 

 and settlement of the country. This rat arrived on the California coast 

 when ships first began to visit San Francisco in numbers. From the coast 

 it spread to the interior, aided no doubt by the active boat traffic along the 

 Sacramento and San Joaquin rivers. At first the rat lived exclusively 

 about human habitations, but in later years it has also taken to living in 

 the wild, and is now so well established out-of-doors in many locations that 

 a person unacquainted with its history would be likely to consider it a 

 native species. 



The Roof Rat is considered to be only a color variety of the Black Rat. 

 It has the long slender tail of the latter, a character which at once dis- 

 tinguishes it from the Norway or Brown Rat. Specimens of the Norway 

 Rat have not as yet been forthcoming from the Yosemite region. The 

 Roof Rat is much more of a climber than the Norway Rat. About maritime 

 ports the former predominates on shipboard. On shore it takes to the 

 roofs and walls of buildings, while the Norway or 'sewer' rat lives in cellars 

 and basements. But along the Sacramento and San Joaquin rivers and 

 their principal tributaries the Roof Rat has taken to living in the piles 

 of drift material and brushy thickets along the river banks. This departure 

 from man-made shelters is made possible by the relatively mild winter of 

 central California, which is closely similar to the winter of the original 

 home of the Roof Rat, in the countries of Asia Minor. Along the coast 

 in central California the Brown Rat has largely supplanted the Roof Rat, 

 and possibly may do so eventually in the interior. 



