This area of California has several rodent and related species marauders but as elsewhere in the U.S the most common rodent pests are the Norway rat, the Roof rat, and the house mouse.
At 7-9 ½ inches long, the Norway rat aka sewer rat, brown rat, or common rat are the larger of the two species with tails shorter than its body length, a stocky appearance, and small ears. They are brown with scattered black hairs; gray to white underside with a blunt muzzle. They reach reproductive maturity within several weeks. Norway rats tend to be the most problematic in coastal or downtown areas.
Roof rats, aka black rats, fruit rats, or house rats, are smaller and sleeker, with tails that are longer than their bodies, with their 16″ total length made up of 6-8″ body plus 6-8″ tail. They have light undersides with a long thin with scaly tail, large ears and eyes. They typically live indoors in attics and outdoors in trees and dense vegetation. They reach reproductive maturity within a few months, allowing them to reproduce quickly.
House mice have slender grayish brown bodies 2 1/2 – 3 3/4″ long with a slightly pointed nose, black protruding eyes, large sparsely-haired ears, and a nearly hairless tail with scale rings and a cream belly. Adults weigh from 1/2 to 1 ounce. In the wild, they often feed on seeds and grain, but will prefer sugar whenever present. Their eclectic diet can include bacon, chocolate, candies, butter, and nutmeats.
It is rare to find both rats and mice inhabiting the same space as rats will chase, hunt, kill, and eat mice.