LYCOS RETRIEVER 
Rats: Norway Rats
built 802 days ago
Rats, mice, and voles have an image problem. The only rats and mice people usually hear of or see are the Norway Rat, Rattus norvegicus, and the common House Mouse, Mus musculus; and most people haven't even heard of voles.
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Norway Rats are suspicious of changes in the environment or new foods, for this reason it may take a couple of days for traps or poison baits to take. Rats are nocturnal, with their peak activity at dusk or before dawn. When the population is large or they are disturbed or hungry, you can see activity during the day.
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Roof rats range along the lower half of the East Coast and throughout the Gulf States and upward into Arkansas. They ... exist along the Pacific Coast and are found on the Hawaiian Islands. The roof rat is apparently not quite as adaptable as the Norway rat, which is one reason it has not spread throughout the country. Its geographic distribution suggests it is more suited to tropical and semi-tropical climates. Occasionally isolated populations are reported from areas not within their normal distribution range; however, these instances are rare. Most of the Great Plains states are free of roof rats but infestations can occur.
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There are two basic types of rats – the black or roof rat and the Norway or brown rat. European settlers probably brought the black rat with them as stowaways, while the Norway arrived around 1775 starting their own revolution by killing off their cousin, the black rat. Today, the Norway rat has taken up residency almost continent-wide, while the black rat has chosen the coastal areas of the southern, southeastern and western United States. In comparison, the Norway rat is slightly larger in appearance.
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Threshold: The Roof and Norway rats are not native to the United States and are ... considered to be exotic. For that reason, the sighting of just one Norway or Roof rat is adequate reason to initiate management efforts addressed at eliminating the rats. Management efforts should continue until all visible signs of the rats are absent. Monitoring for the detection of a new rat infestation should continue year-round.
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There are two primary species of rats present in the Pacific Northwest: The Norway rat and the roof rat. The Norway rat is both larger and heavier than the roof rat. It has a wider distribution and is usually more common, although the roof rat may be abundant in some localities, usually near coastal areas. Norway rats build their nests in burrows under buildings, low shrubs or ground cover, wood piles, yard accumulations of junk, and garbage dumps. The roof rat, on the other hand, is a better climber than the Norway rat and is more likely to build its nest in walls, attics, vines or trees.
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Norway Rats