Could be voles. Also known as field or meadow mice, voles are small rodents that resemble hamsters. With a compact, heavy body, short legs, a short-furred tail, they can measure 5 to 8 inches long, including the tail.
These rodents are plant eaters, with an appetite for a lot of different plants – from artichokes, carrots, lettuce, spinach, and tomato, to lilies and dichondra. Voles will gnaw the bark of fruit trees including almond, apple, avocado, cherry, citrus, and olive, a few inches aboveground to a few inches below ground. If voles gnaw completely around the trunk or roots, it will disrupt the tree’s flow of nutrients and water, a process known as girdling. Girdling damage on trunks and roots can kill trees.
Voles are active both day and night and do not hibernate. They build complex tunnels under dense ground cover such as lawns, grasses, and meadows, living in colonies. Reproducing at a rapid rate, a single pair of voles can rapidly become a vole kingdom!
In addition to gnaw marks about one-eighth inch wide and three-eighths inch long in irregular patches and various angles, you might also observe droppings, runways, and burrows. You may see holes with a diameter of around one and a half inches close to their surface runways, damage to the roots of trees, yellowed and wilting plants, missing bulbs, teeth marks around the bottom of trees and shrubs, and irregular paths of one to two inches of trampled grass or soil.
The most effective ways to manage voles are:
Modify their habitat – Remove weeds, heavy mulch, and dense vegetation where they can hide. Mow grassy areas adjacent to gardens.
Exclude them – Install wire fences at least 12 inches above the ground with a mesh size of one-quarter inch or smaller (these can stand alone or be attached to the bottom of an existing fence). Bury the bottom edge of the fence 6 to 10 inches to prevent voles from tunneling beneath it. Protect young trees, vines, and ornamentals by using cylinders made from hardware cloth, sheet metal, or heavy plastic that surround the trunk.
Trap them – Use a sufficient number of traps to control the population – at least a dozen traps for a small garden. Simple, wooden mouse traps baited with a peanut butter-oatmeal mixture or apple slices work well. Trap placement is crucial. Voles seldom stray from their runways, so set traps along these routes. Look for burrows and runways in grass or mulch in or near the garden. Place the traps at right angles to the runways with the trigger end in the runway. Examine traps daily, removing dead voles or resetting sprung traps as needed. Continue to trap in one location until you stop catching voles then move the trap to a new location 15 to 20 feet away. Destroy old runways or burrows with a shovel or rototiller to deter new voles from immigrating to the site.