Controlling Rats and Mice
Having a few rats or mice on your property isn't a pest problem unless they are doing damage or posing a health risk. However, the rodent population can quickly get out of hand if food and shelter are available. Humane and effective management of rats and mice involves blocking access points, removing food sources, making the habitat undesirable for rodents to live in, and possibly using live traps or snap traps to eliminate remaining rodents.
Step 1: Rodent-Proof Structures
If rodents are coming into your house, garage, chicken coop, or other structure, the first and most important step is to rodent-proof it. Do a thorough inspection of the structure for possible entry points- chimneys, gaps under doors (including the garage door), holes near the foundation, and any other gaps larger than 1/4 inch may be allowing rodents in. If you find an entry point, it's still important to inspect the rest of the structure in case there are more. If you cannot find any, have an inspection done by a professional.
Close off whatever entry points you find. 1/4 or 1/8 inch hardware cloth, silicone caulking (which must be monitored for gnawing), and steel wool can be useful for small gaps and holes. Metal or rubber door bottoms can keep rodents from scurrying under doors, as long as the doors are not left open by accident. If your chimney is an entry point, install a screened chimney cap and a top-sealing damper to help keep rodents out. (The chimney cap alone may discourage rodents, but the mesh is not small enough to actually exclude them. It is a violation of California building codes and a fire hazard to install mesh smaller than 5/8 inch in chimneys.)
Step 2: Identify and Remove Food Sources
After eliminating entry points on structures, or as a first step if the rodent problem is not in a structure, find out what has been attracting the rodents. Most often, this is a food source- such as a fruit tree, birdfeeder, compost pile, or food bowl for a pet. Once you have identified the attractant(s), take steps to prevent rodents from accessing them. For example, if you determine that a birdfeeder is attracting unwanted visitors, you could take it down and replace it with one that is less of a draw for rodents, such as a thistle feeder. (Clean up any leftover birdseed from the ground, too.) If the rodents in your yard are being attracted by a fruit tree, try to harvest the fruit more frequently.
Step 3: Habitat Modification
The next thing to do, once you have removed or reduced the main attractant(s), is make the rodents feel less safe in your yard. Cut back vines and other greenery, especially near buildings, to eliminate cover. Rats and mice tend to avoid venturing out in the open where predators can find them. You can even make your yard more desirable to natural predators such as owls, or encourage your cat or dog to establish its presence there to deter rodents. Don't relocate animals such as snakes to your yard however. If they are not already there, it means the habitat is not suitable for them, and they will likely die or leave before they start lowering the rodent population.
Step 4: Remove Stragglers
Traps are not necessary for every rodent problem. However, if you have rodent-proofed a structure and find rodents inside that were closed in by the rodent-proofing efforts, you will need to trap them. You can either capture them in livetraps and release them outside (on your own property, since releasing them in an unfamiliar environment is inhumane), or use snap traps, which are a relatively humane form of lethal control. Never use glue traps or poison, both of which are cruel and pose dangers to humans and pets.
Use the traps, whichever kind you choose, until you remove any rodents that were left inside a structure. Don't try to control an outdoor rodent problem with traps because you will never be able to trap all the rodents (and even if you could, more would come for the same attractants). Instead, keep up with attractant removal and habitat modification, and remember that having a few rodents on your property- as long as they are not in a building or causing other problems- is unavoidable and okay.