Species’ names:

Red fox, Vulpes vulpes
Gray fox, Urocyon cinereoargenteus

Size: 10–15 pounds; Body: 20–25″ long; Gray fox is smaller

Signs of their presence:

Sounds: May scream, yap, growl, or bark.

Scats: Twisted, often contain hair or berries, deposited on rocks or logs.

Odor: Their scent markings have distinctive odors. Red fox urine smells skunky, while gray fox urine smells musky.

Common nuisance situations:

Time of year: Any time of year.

Their mere presence may frighten some people.

Getting into chicken (or turkey, duck, or goose) coop or yard. May take piglets, lambs, and small pets.

In the spring, they may den underneath a porch or in a yard for a while, while they’re raising their pups. Foxes generally use more than one den to raise their pups and may move them as many as 2–4 times, so this may be a short-term situation. They’ll usually leave by the end of June at the latest. These dens aren’t used during other seasons.

Foxes (and coyotes) will chew holes in irrigation pipes in fields and orchards.

Disease risks: Rabies, distemper. Red foxes, but not gray, get mange.

For more information:
http://www.nwco.net/08-AppendixBNuisanceSpecies/8-04-Foxes.asp