ALEXANDRINE RAT. Rattus rattus alexandrinus (Geoffroy)

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 7-1/4 to 8 inches (182-205 mm.), tail 8-1/3 to 10 inches (213-250 mm.), hind foot about 1-1/2 inches (36-39 mm.), ear from crown about 1 inch (23-26 mm.); weight under 1/2 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. Recorded 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 distinguishes 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.

At Snelling, in January, 1915, a number of roof rats were taken in piles of drift and thickets along the Merced River. There were old deserted nests of the Streator Wood Rat in the same locality and the suggestion presented was that possibly the alien, with similar associational predilections, had driven out the native species. Along the Tuolumne River below Lagrange the roof rats had made numerous pathways which were at first mistaken for large runs of meadow mice. At El Portal two of the rats were captured November 23 and 25, 1914, in the upper stories of the large hotel building then there. The species is unknown at Coulterville, according to Mr. Donald D. McLean, though House Mice are present there. The mice are transported readily in bales of hay hauled on wagons, but the rats require larger vehicles such as river boats or railroad cars.