field mouse

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various small mice or voles, especially of the North American genus Microtus or the Eurasian genus Apodemus, inhabiting meadows and fields and often causing damage to crops.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun North America A small vole such as the meadow vole.
• noun One of several species of mice in genus Apodemus found in Eurasia and Africa.
• noun One of several species of mice in genus Akodon found in South America.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various small mouselike rodents of the family Cricetidae (especially of genus Microtus) having a stout short-tailed body and inconspicuous ears and inhabiting fields or meadows
• noun any nocturnal Old World mouse of the genus Apodemus inhabiting woods and fields and gardens